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RTEMS C User's Guide

1. 219 CONFIGURE MAXIMUM PORTS 219 CONFIGURE MAXIMUM POSIX CONDITION VARIABLES EET 220 CONFIGURE MAXIMUM POSIX KEYS 220 CONFIGURE MAXIMUM POSIX MESSAGE QUEUES 220 CONFIGURE MAXIMUM POSIX MUTEXES 220 CONFIGURE MAXIMUM POSIX QUEUED SIGNALS 220 CONFIGURE MAXIMUM POSIX SEMAPHORES 220 CONFIGURE MAXIMUM POSIX THREADS 220 CONFIGURE MAXIMUM POSIX TIMERS 220 CONFIGURE MAXIMUM REGIONS 219 CONFIGURE MAXIMUM SEMAPHORES 218 CONFIGURE MAXIMUM TASKS 00 218 CONFIGURE MAXIMUM TIMERS esses 218 CONFIGURE MAXIMUM USER EXTENSIONS 219 CONFIGURE MEMORY OVERHEAD 217 CONFIGURE_MICROSECONDS_PER_TICK 217 CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS 218 CONFIGURE_MP_MAXIMUM_NODES 218 CONFIGURE_MP_MAXIMUM_PROXIES 218 CONFIGURE_MP_MPCI_TABLE_POINTER 218 CONFIGURE MP NODE NUMBER 218 CONFIGURE NUMBER OF TERMIOS PORTS 216 CONFIGURE POSIX HAS OWN INIT THREAD TABLE Aiea Cheese eied e te A tas 220 CONFIGURE_POSIX_INIT_THREAD_ENTRY_POINT sede ded due Sass Sooke ded egeris viis 220 CONFIGURE POSIX INIT THREAD STACK SIZE 220 CONFIGURE POSIX INIT THREAD TABLE 220 CONFIGURE RTEMS INIT TASKS TABLE 219 CONFIGURE_TERMIOS_DISABLED 216 CONF
2. RMS only calls for task 1 to have the lowest priority task 4 to have the highest priority and tasks 2 and 3 to have an equal priority between that of tasks 1 and 4 The actual RTEMS priorities assigned to the tasks must only adhere to those guidelines Many applications have tasks with both hard and soft deadlines The tasks with hard deadlines are typically referred to as the critical task set with the soft deadline tasks being the non critical task set The critical task set can be scheduled using RMS with the non critical tasks not executing under transient overload by simply assigning priorities such that the lowest priority critical task i e longest period has a higher priority than the highest priority non critical task Although RMS may be used to assign priorities to the non critical tasks it is not necessary In this instance schedulability is only guaranteed for the critical task set 19 2 4 Schedulability Analysis RMS allows application designers to ensure that tasks can meet all deadlines even under transient overload without knowing exactly when any given task will execute by applying proven schedulability analysis rules Chapter 19 Rate Monotonic Manager 183 19 2 4 1 Assumptions The schedulability analysis rules for RMS were developed based on the following assump tions e The requests for all tasks for which hard deadlines exist are periodic with a constant interval between requests e Each tas
3. 0 0008 145 RMS Algorithm definition esses 182 RMS First Deadline Rule s 184 RMS Processor Utilization Rule 183 RMS schedulability analysis 182 round robin scheduling 04 176 RTEMS API Configuration Table 225 RTEMS Configuration Table 222 runtime driver registration 158 S scheduling sie irria Ee peers 175 scheduling mechanisms 0 175 segment definition 08 135 Semaplioreg osetechn Ie I BRREP RV a DU PES 85 send event set to a task 5 118 send message to a queue sse 107 send signal set ies er erre epREVEREEPG 125 set task mode wi tose ele ee ERU ERE 48 set task notepad entry 00005 50 set task preemption mode 0005 48 Sel task prlobhby cepe RESU Rer UP weeitisiers 47 set the time of day v bore rr ER YES 68 shutdown RLEMS 21e Sdn Ganesan E ER 21 signal set building 5 eee e eme s 121 signals iueerenizeeex P rA ERE PPEPL REPRE 121 269 special device services 0 e eee eee 170 sporadic task definition 00 181 start current period 0 eee eee ee eee 196 start multitasking c s2200siiwessueiadasdeaive 26 Starting a task io scene ERU REURER EE 41 suspending a task 0 eee ee eee eee 44 T task arGuiments is sccw
4. 115 11 2 83 Building an EVENT RECEIVE Option Set 116 11 3 Operations sees a see tac eh vas SERRE dA Re EE EPOR RE dade 116 11 3 1 Sending an Event Set 0 eee eee 116 11 8 2 Receiving an Event Set 0 0 116 11 3 3 Determining the Pending Event Set 117 11 3 4 Receiving all Pending Events 2000 117 11 4 D rectlveSiciiise1se o desggo cue s P A tite d HEAR RUND USER 1 11 4 1 EVENT SEND Send event set to a task 118 11 4 2 EVENT RECEIVE Receive event condition 119 vi RTEMS C User s Guide 12 Signal Manager cc oos eere re sex neces 121 12 4 Introduction i5 nnd este Ela abre ie e ON 121 12 2 Backgrounds e ecce eed Lp aces ere igo rea ean 121 12 2 1 Signal Manager Definitions 00 e eae 121 12 2 2 A Comparison of ASRs and ISRs 2004 121 12 2 3 Building a Signal Set 20 c cece eee ee eee 121 12 2 4 Building an ASR Mode 0 cece eee eee 122 12 9 Operations 1 Loos tutti ed exer de e RE esu coda O REST d 122 12 3 1 Establishing an ASR 2 eee eee 122 12 3 2 Sending a Signal Set 2 ccc eee eee eens 123 12 3 8 Processing an ASR esee gar ee 123 12 4 Directives c vicscvetes ee pUPOSo be ETUR ERRARE RRPR EU UNES TCR 123 12 4 4 SIGNAL_CATCH Establish an ASR 124 12 4 3 SIGNAL SEND Send signal set to a task 125
5. Deadline Task Task Task Total All Deadlines Time 1 2 3 Execution Time Net 100 1 1 1 25 50 100 175 NO 200 2 1 1 50 50 100 200 YES The key to this analysis is to recognize when each task will execute For example at time 100 task 1 must have met its first deadline but tasks 2 and 3 may also have begun execution Chapter 19 Rate Monotonic Manager 185 In this example at time 100 tasks 1 and 2 have completed execution and thus have met their first deadline Tasks 1 and 2 have used 25 50 75 time units leaving 100 75 25 time units for task 3 to begin Because task 3 takes 100 ticks to execute it will not have completed execution at time 100 Thus at time 100 all of the tasks except task 3 have met their first deadline At time 200 task 1 must have met its second deadline and task 2 its first deadline As a result of the first 200 time units task 1 uses 2 25 50 and task 2 uses 50 leaving 200 100 time units for task 3 Task 3 requires 100 time units to execute thus it will have completed execution at time 200 Thus all of the tasks have met their first deadlines at time 200 and the task set is schedulable using the First Deadline Rule 19 2 4 6 Relaxation of Assumptions The assumptions used to develop the RMS schedulability rules are uncommon in most real time systems For example it was assumed that tasks have constant unvarying execution time It is possible to relax thi
6. DIRECTIVE STATUS CODES NONE DESCRIPTION This directive disables all maskable interrupts and returns the previous level A later invocation of the rtems_interrupt_enable directive should be used to restore the interrupt level NOTES This directive will not cause the calling task to be preempted This directive is implemented as a macro which modifies the level parameter 62 RTEMS C User s Guide 6 4 3 INTERRUPT_ENABLE Enable Interrupts CALLING SEQUENCE void rtems_interrupt_enable rtems_interrupt_level level 3 DIRECTIVE STATUS CODES NONE DESCRIPTION This directive enables maskable interrupts to the level which was returned by a previous call to rtems_interrupt_disable Immediately prior to invoking this directive maskable interrupts should be disabled by a call to rtems_interrupt_disable and will be enabled when this directive returns to the caller NOTES This directive will not cause the calling task to be preempted Chapter 6 Interrupt Manager 63 6 4 4 INTERRUPT_FLASH Flash Interrupts CALLING SEQUENCE void rtems_interrupt_flash rtems_interrupt_level level 3 DIRECTIVE STATUS CODES NONE DESCRIPTION This directive temporarily enables maskable interrupts to the level which was returned by a previous call to rtems_interrupt_disable Immediately prior to invoking this directive maskable interrupts should be disabled by a call to rtems_interrupt_disable and will be redisabled when this dire
7. The rtems interrupt catch directive connects a procedure to an interrupt vector The vector number is managed using the rtems vector number data type The interrupt service routine is assumed to abide by these conventions and have a prototype similar to the following rtems isr user isr rtems vector number vector 25 The vector number argument is provided by RTEMS to allow the application to identify the interrupt source This could be used to allow a single routine to service interrupts from multiple instances of the same device For example a single routine could service interrupts from multiple serial ports and use the vector number to identify which port requires servicing To minimize the masking of lower or equal priority level interrupts the ISR should perform the minimum actions required to service the interrupt Other non essential actions should be handled by application tasks Once the user s ISR has completed it returns control to the RTEMS interrupt manager which will perform task dispatching and restore the registers saved before the ISR was invoked 58 RTEMS C User s Guide The RTEMS interrupt manager guarantees that proper task scheduling and dispatching are performed at the conclusion of an ISR A system call made by the ISR may have readied a task of higher priority than the interrupted task Therefore when the ISR completes the postponed dispatch processing must be performed No dispatch processing is perform
8. Control software for special peripheral devices used by the applica tion RTEMS provided routines that provide support mechanisms for real time applications The act of loading a task s context onto the CPU and transferring control of the CPU to that task The state entered by a task after it is created and before it has been started A table which contains the entry points for each of the configured device drivers A term used to describe memory which can be accessed at two dif ferent addresses An application that is delivered as a hidden part of a larger system For example the software in a fuel injection control system is an embedded application found in many late model automobiles A buffer provided by the MPCI layer to RTEMS which is used to pass messages between nodes in a multiprocessor system It typically Chapter 26 Glossary 255 contains routing information needed by the MPCI The contents of an envelope are referred to as a packet entry point The address at which a function or task begins to execute In C the entry point of a function is the function s name events A method for task communication and synchronization The direc tives provided by the event manager are used to service events exception A synonym for interrupt executing The task state entered by a task after it has been given control of the CPU executive In this document this term is used to referred to RTEMS Com monly an
9. NOTES The requesting task can suspend itself by specifying RTEMS SELF as id In this case the task will be suspended and a successful return code will be returned when the task is resumed Suspending a global task which does not reside on the local node will generate a request to the remote node to suspend the specified task If the task specified by id is already suspended then the RTEMS ALREADY SUSPENDED status code is returned Chapter 5 Task Manager 45 5 4 7 TASK RESUME Resume a task CALLING SEQUENCE rtems status code rtems task resume rtems id id 25 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL task restarted successfully RTEMS INVALID ID task id invalid RTEMS INCORRECT STATE task not suspended DESCRIPTION This directive removes the task specified by id from the suspended state If the task is in the ready state after the suspension is removed then it will be scheduled to run If the task is still in a blocked state after the suspension is removed then it will remain in that blocked state NOTES The running task may be preempted if its preemption mode is enabled and the local task being resumed has a higher priority Resuming a global task which does not reside on the local node will generate a request to the remote node to resume the specified task If the task specified by id is not suspended then the RTEMS INCORRECT STATE status code is returned 46 RTEMS C User s Guide 5 4
10. e an atomic unit of a real time multiprocessor system e single threads of execution which concurrently compete for resources e a sequence of closely related computations which can execute concurrently with other computational sequences From RTEMS perspective a task is the smallest thread of execution which can compete on its own for system resources A task is manifested by the existence of a task control block TCB 30 RTEMS C User s Guide 5 2 2 Task Control Block The Task Control Block TCB is an RTEMS defined data structure which contains all the information that is pertinent to the execution of a task During system initialization RTEMS reserves a TCB for each task configured A TCB is allocated upon creation of the task and is returned to the TCB free list upon deletion of the task The TCB s elements are modified as a result of system calls made by the application in response to external and internal stimuli TCBs are the only RTEMS internal data structure that can be accessed by an application via user extension routines The TCB contains a task s name ID current priority current and starting states execution mode set of notepad locations TCB user extension pointer scheduling control structures as well as data required by a blocked task A task s context is stored in the TCB when a task switch occurs When the task regains control of the processor its context is restored from the TCB When a task is resta
11. should not return printf rtems task delete returned with status of d n status exit 1 rtems_task user_application rtems_task_argument argument 252 RTEMS C User s Guide 1 application specific initialization goes here while 1 1 infinite loop APPLICATION CODE GOES HERE This code will typically include at least one directive which causes the calling task to give up the processor define CONFIGURE_TEST_NEEDS_CONSOLE_DRIVER for stdio define CONFIGURE_TEST_NEEDS_CLOCK_DRIVER for time services define CONFIGURE_MAXIMUM_TASKS 2 define CONFIGURE_INIT_TASK_NAME rtems build name E X A M define CONFIGURE_RTEMS_INIT_TASKS_TABLE define CONFIGURE_INIT include lt confdefs h gt Chapter 26 Glossary 26 Glossary active aperiodic task application ASR asynchronous 253 A term used to describe an object which has been created by an application A task which must execute only at irregular intervals and has only a soft deadline In this document software which makes use of RTEMS see Asynchronous Signal Routine Not related in order or timing to other occurrences in the system Asynchronous Signal Routine awakened big endian bit mapped block blocked broadcast BSP Similar to a hardware interrupt except that it is associated with a task and is run in the context of a task The directives provided b
12. In multiprocessor real time systems new requirements such as sharing data and global resources between processors are introduced This requires an efficient and reliable com munications vehicle which allows all processors to communicate with each other as necessary In addition the ramifications of multiple processors affect each and every characteristic of a real time system almost always making them more complicated RTEMS addresses these issues by providing simple and flexible real time multiprocessing capabilities The executive easily lends itself to both tightly coupled and loosely coupled configurations of the target system hardware In addition RTEMS supports systems com posed of both homogeneous and heterogeneous mixtures of processors and target boards A major design goal of the RTEMS executive was to transcend the physical boundaries of the target hardware configuration This goal is achieved by presenting the application software with a logical view of the target system where the boundaries between processor nodes are transparent As a result the application developer may designate objects such as tasks queues events signals semaphores and memory blocks as global objects These global objects may then be accessed by any task regardless of the physical location of the object and the accessing task RTEMS automatically determines that the object being accessed resides on another processor and performs the actions required to acc
13. RTEMS SUCCESSFUL partition deleted successfully RTEMS INVALID ID invalid partition id RTEMS RESOURCE IN USE buffers still in use RTEMS ILLEGAL ON REMOTE OBJECT cannot delete remote partition DESCRIPTION This directive deletes the partition specified by id The partition cannot be deleted if any of its buffers are still allocated The P TCB for the deleted partition is reclaimed by RTEMS NOTES This directive will not cause the calling task to be preempted The calling task does not have to be the task that created the partition Any local task that knows the partition id can delete the partition When a global partition is deleted the partition id must be transmitted to every node in the system for deletion from the local copy of the global object table The partition must reside on the local node even if the partition was created with the RTEMS GLOBAL option Chapter 13 Partition Manager 133 13 4 4 PARTITION_GET_BUFFER Get buffer from a partition CALLING SEQUENCE rtems_status_code rtems_partition_get_buffer rtems_id id void buffer i DIRECTIVE STATUS CODES RTEMS SUCCESSFUL buffer obtained successfully RTEMS INVALID ADDRESS buffer is NULL RTEMS INVALID ID invalid partition id RTEMS UNSATISFIED all buffers are allocated DESCRIPTION This directive allows a buffer to be obtained from the partition specified in id The address of the allocated buffer is returned in buffer NO
14. rtems_device_major_number major rtems_device_minor_number minor void argument DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL successfully initialized RTEMS_INVALID_NUMBER invalid major device number DESCRIPTION This directive calls the device driver initialization routine specified in the Device Driver Table for this major number This directive is automatically invoked for each device driver when multitasking is initiated via the initialize_executive directive A device driver initialization module is responsible for initializing all hardware and data structures associated with a device If necessary it can allocate memory to be used during other operations NOTES This directive may or may not cause the calling task to be preempted This is dependent on the device driver being initialized 164 RTEMS C User s Guide 16 4 4 IO REGISTER NAME Register a device CALLING SEQUENCE rtems status code rtems io register name const char name rtems device major number major rtems device minor number minor DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL successfully initialized RTEMS_TOO_MANY too many devices registered DESCRIPTION This directive associates name with the specified major minor number pair NOTES This directive will not cause the calling task to be preempted Chapter 16 I O Manager 165 16 4 5 IO LOOKUP NAME Lookup a device CALLING SEQUENCE rtems status code rtems io lookup name const c
15. s Guide Chapter 12 Signal Manager 121 12 Signal Manager 12 1 Introduction The signal manager provides the capabilities required for asynchronous communication The directives provided by the signal manager are e rtems_signal_catch Establish an ASR e rtems_signal_send Send signal set to a task 12 2 Background 12 2 1 Signal Manager Definitions The signal manager allows a task to optionally define an asynchronous signal routine ASR An ASR is to a task what an ISR is to an application s set of tasks When the processor is interrupted the execution of an application is also interrupted and an ISR is given control Similarly when a signal is sent to a task that task s execution path will be interrupted by the ASR Sending a signal to a task has no effect on the receiving task s current execution state A signal flag is used by a task or ISR to inform another task of the occurrence of a significant situation Thirty two signal flags are associated with each task A collection of one or more signals is referred to as a signal set The data type rtems_signal_set is used to manipulate signal sets A signal set is posted when it is directed or sent to a task A pending signal is a signal that has been sent to a task with a valid ASR but has not been processed by that task s ASR 12 2 2 A Comparison of ASRs and ISRs The format of an ASR is similar to that of an ISR with the following exceptions e ISRs are sch
16. 00 0 e eee ee eee 159 10 4 JD recllveSsc lii scmelerfiwee a E lude Ru UI 6e 160 vii vili RTEMS C User s Guide 16 4 1 IO_REGISTER_DRIVER Register a device driver 161 16 4 IO UNREGISTER DRIVER Unregister a device driver PE AE e E ex DEM LL d E 162 16 4 8 IO INITIALIZE Initialize a device driver 163 16 4 4 IO REGISTER NAME Register a device 164 16 4 5 IO LOOKUP NAME Lookup a device 165 16 4 6 IO OPEN Open a device 00 cece eee eee ee 166 16 4 7 IO CLOSE Close a device 0 000 c cee eee eee 167 16 4 8 IO READ Read from a device 0045 168 16 4 9 IO WRITE Write to a device 0 cece eee 169 16 4 10 IO CONTROL Special device services 170 1T Fatal Error NMIgnager i l ee 171 IT l IntroduetiOnu err ERR ERESRREUDUCRE eens 171 17 2 Background sa A e LR ERROR RD ERE ERE RON 171 17 9 Operations o esesert ecrit De e aE E pA be Rede 171 17 3 1 Announcing a Fatal Error 0 e eee eee 171 VTA Directives srr neueste RR Rp ht A E eles cuite noe eta 172 17 4 1 FATAL ERROR OCCURRED Invoke the fatal error handler sc ceceraveiera sie teweeweie ne EEEE SE DUIS pea 173 18 Scheduling Concepts 175 18 1 Introduction 4 bee Rr RERO aoa ee nhaeeens 175 18 2 Scheduling Mechanisms 0000 eee eee eee eens 175 18 2 1 Task Priority and Scheduling soris siissicir
17. Each task has a priority associated with it at all times The initial value of this priority is assigned at task creation time The priority of a task may be changed at any subsequent time Chapter 5 Task Manager 31 Priorities are used by the scheduler to determine which ready task will be allowed to execute In general the higher the logical priority of a task the more likely it is to receive processor execution time 5 2 5 Task Mode A task s execution mode is a combination of the following four components e preemption e ASR processing e timeslicing e interrupt level It is used to modify RTEMS scheduling process and to alter the execution environment of the task The data type rtems_task_mode is used to manage the task execution mode The preemption component allows a task to determine when control of the processor is relinquished If preemption is disabled RTEMS_NO_PREEMPT the task will retain control of the processor as long as it is in the executing state even if a higher priority task is made ready If preemption is enabled RTEMS_PREEMPT and a higher priority task is made ready then the processor will be taken away from the current task immediately and given to the higher priority task The timeslicing component is used by the RTEMS scheduler to determine how the processor is allocated to tasks of equal priority If timeslicing is enabled RTEMS_TIMESLICE then RTEMS will limit the amount of time the task can ex
18. Priority Geilng aio necne denen rey Ede ei tein ae 86 9 2 5 Building a Semaphore Attribute Set 005 87 9 2 6 Building a SEMAPHORE_OBTAIN Option Set 88 9 3 Operations ssis best er erased deus RR QNA OE ne eae de 88 9 3 1 Creating a Semaphore 0 cece eee eee eee 88 9 3 2 Obtaining Semaphore IDs 0 0 88 9 3 3 Acquiring a Semaphore 0 cece eee eee ee eee 88 9 3 4 Releasing a Semaphore 0 00 cece eee eee ee eee 89 9 3 5 Deleting a Semaphore 0 0 c cece eee eee eee 89 OA JDITC CHIVES cee sara tecin alias bcade ore TIU PUR tes eam poc 90 9 4 1 SEMAPHORE CREATE Create a semaphore 91 9 4 2 SEMAPHORE_IDENT Get ID of a semaphore 93 9 4 3 SEMAPHORE DELETE Delete a semaphore 94 9 4 5 SEMAPHORE_OBTAIN Acquire a semaphore 95 9 4 5 SEMAPHORE RELEASE Release a semaphore 97 9 4 6 SEMAPHORE FLUSH Unblock all tasks waiting on a Semaphore ns xu skids eadi Realtor tenant Is ab dut Yon on E LR Urdu a 98 10 Message Manager ss 99 11 10 0 Introduction eed dte aen b s ace E ee totis 99 10 2 Background ooi ke roe EE EE a Rd 99 10 2 1 MeSSageS essor rct ERR ERU ee ysis do 4a GAN 99 10 2 2 Message Queues 0 0 cece cece eee ene 99 10 2 3 Building a Message Queue Attribute Set 99 10 2 4 Building a MESSAGE QUEUE RECEIVE Option Set 100 1
19. The timer is scheduled to fire after an interval ticks clock ticks has passed When the timer fires the timer service routine routine will be invoked with the argument user data NOTES This directive will not cause the running task to be preempted Chapter 8 Timer Manager 79 8 4 6 TIMER FIRE WHEN Fire timer when specified CALLING SEQUENCE rtems status code rtems timer fire when rtems id id rtems time of day wall time rtems timer service routine entry routine void user data DIRECTIVE STATUS CODES RTEMS SUCCESSFUL timer initiated successfully RTEMS INVALID ADDRESS routine is NULL RTEMS INVALID ADDRESS wall time is NULL RTEMS INVALID ID invalid timer id RTEMS NOT DEFINED system date and time is not set RTEMS INVALID CLOCK invalid time of day DESCRIPTION This directive initiates the timer specified by id If the timer is running it is automatically canceled before being initiated The timer is scheduled to fire at the time of day specified by wall time When the timer fires the timer service routine routine will be invoked with the argument user data NOTES This directive will not cause the running task to be preempted 80 RTEMS C User s Guide 8 4 7 TIMER_INITIATE_SERVER Initiate server for task based timers CALLING SEQUENCE rtems_status_code rtems_timer_initiate_server uint32_t priority uint32_t stack_size rtems_attribute attribute_set 25 DIRE
20. each object type s control block is different However many of the fields are similar in func tion The number of each type of control block is application dependent and determined by the values specified in the user s Configuration Table An object control block is allocated at object create time and freed when the object is deleted With the exception of user extension routines object control blocks are not directly manipulated by user applications 2 3 Communication and Synchronization In real time multitasking applications the ability for cooperating execution threads to com municate and synchronize with each other is imperative A real time executive should provide an application with the following capabilities e Data transfer between cooperating tasks Chapter 2 Key Concepts 15 e Data transfer between tasks and ISRs e Synchronization of cooperating tasks e Synchronization of tasks and ISRs Most RTEMS managers can be used to provide some form of communication and or syn chronization However managers dedicated specifically to communication and synchroniza tion provide well established mechanisms which directly map to the application s varying needs This level of flexibility allows the application designer to match the features of a particular manager with the complexity of communication and synchronization required The following managers were specifically designed for communication and synchronization e Semaphore e
21. message queue flushed successfully RTEMS INVALID ADDRESS count is NULL RTEMS INVALID ID invalid queue id DESCRIPTION This directive removes all pending messages from the specified queue id The number of messages removed is returned in count If no messages are present on the queue count is set to zero NOTES Flushing all messages on a global message queue which does not reside on the local node will generate a request to the remote node to actually flush the specified message queue 114 RTEMS C User s Guide Chapter 11 Event Manager 115 11 Event Manager 11 1 Introduction The event manager provides a high performance method of intertask communication and synchronization The directives provided by the event manager are e rtems_event_send Send event set to a task e rtems_event_receive Receive event condition 11 2 Background 11 2 1 Event Sets An event flag is used by a task or ISR to inform another task of the occurrence of a significant situation Thirty two event flags are associated with each task A collection of one or more event flags is referred to as an event set The data type rtems_event_set is used to manage event sets The application developer should remember the following key characteristics of event oper ations when utilizing the event manager e Events provide a simple synchronization facility e Events are aimed at tasks e Tasks can wait on more than one event simultaneously e
22. the value for this field corresponds to the setting of the macro CONFIGURE MAXIMUM PORTS If not defined by the application then the CONFIGURE MAXIMUM PORTS macro defaults to 0 number of initialization tasks is the number of initialization tasks configured At least one RTEMS initialization task or POSIX initializatin must be configured in or der for the user s application to begin executing When using the confdefs h mechanism for configuring an RTEMS application the user must define the CONFIGURE RTEMS INIT TASKS TABLE to indi cate that there is one or more RTEMS initialization task If the application only has one RTEMS initialization task then the auto matically generated Initialization Task Table will be sufficient The following macros correspond to the single initialization task Chapter 22 Configuring a System 227 e CONFIGURE_INIT_TASK_NAME is the name of the task If this macro is not defined by the application then this defaults to the task name of UI1 for User Initialization Task 1 e CONFIGURE_INIT_TASK_STACK_SIZE is the stack size of the single initialization task If this macro is not defined by the application then this defaults to RTEMS_MINIMUM_STACK_ SIZE e CONFIGURE_INIT_TASK_PRIORITY is the initial priority of the single initialization task If this macro is not defined by the application then this defaults to 1 e CONFIGURE_INIT_TASK_ATTRIBUTES is the attributes of the single initializatio
23. 0 00 eee eee 72 8 3 4 Initiating a Time of Day Timer 2005 2 8 3 5 Canceling a Timer ii est ERR LSU ER e T3 8 3 6 Resetting a Timer ccc eee eee eens 73 8 3 7 Initiating the Timer Server 000 c eee eee eee 73 8 3 8 Deleting imer covenant hm REPERI LEER Ra 73 OA DIE CUIVES a ecciesie poeti stare RUE PERS e AER numen ants 73 8 4 1 TIMER_CREATE Create a timer 05 74 8 4 2 TIMER IDENT Get ID of a timer 15 8 4 3 TIMER CANCEL Cancel a timer sseessesse 76 8 4 4 TIMER_DELETE Delete a timer 77 8 4 5 TIMER_FIRE_AFTER Fire timer after interval 78 8 4 6 TIMER_FIRE_WHEN Fire timer when specified 79 8 4 7 TIMER_INITIATE_SERVER Initiate server for task based pir eee 80 8 4 8 TIMER SERVER FIRE AFTER Fire task based timer ater dntervalo eis edt ER Rr oa e suited Re ER ecd 81 8 4 9 TIMER SERVER FIRE WHEN Fire task based timer when Specified ss iuis sese eqebIpe reser DEEPER STENDE AN os 82 8 4 10 TIMER RESET Reset an interval timer 83 9 Semaphore Manager 85 91 Introduction 452i rebar re rrr orte ebd e rice qa ne 85 9 2 Background sorses eieren RR eru eR RERELEN EROR EE pr 85 9 2 1 Nested Resource Access esses 85 9 2 2 Priority Inversion svite c ara cece eee ees 86 9 2 3 Priority Inheritance ss esce da eterne not Rees 86 9 24
24. 1 Establishing an ASR The rtems signal catch directive establishes an ASR for the calling task The address of the ASR and its execution mode are specified to this directive The ASR s mode is distinct from the task s mode For example the task may allow preemption while that task s ASR may have preemption disabled Until a task calls rtems signal catch the first time its ASR is invalid and no signal sets can be sent to the task A task may invalidate its ASR and discard all pending signals by calling rtems signal catch with a value of NULL for the ASR s address When a task s ASR is invalid new signal sets sent to this task are discarded A task may disable ASR processing RTEMS_NO_ASR via the task_mode directive When a task s ASR is disabled the signals sent to it are left pending to be processed later when the ASR is enabled Chapter 12 Signal Manager 123 Any directive that can be called from a task can also be called from an ASR A task is only allowed one active ASR Thus each call to rtems_signal_catch replaces the previous one Normally signal processing is disabled for the ASR s execution mode but if signal processing is enabled for the ASR the ASR must be reentrant 12 3 2 Sending a Signal Set The rtems_signal_send directive allows both tasks and ISRs to send signals to a target task The target task and a set of signals are specified to the rtems_signal_send directive The sending of a signal to a t
25. 14 Region Manager 145 14 4 6 REGION RETURN SEGMENT Return segment to a region CALLING SEQUENCE rtems status code rtems region return segment rtems id id void segment DIRECTIVE STATUS CODES RTEMS SUCCESSFUL segment returned successfully RTEMS INVALID ADDRESS segment is NULL RTEMS INVALID ID invalid region id RTEMS INVALID ADDRESS segment address not in region DESCRIPTION This directive returns the segment specified by segment to the region specified by id The returned segment is merged with its neighbors to form the largest possible segment The first task on the wait queue is examined to determine if its segment request can now be satisfied If so it is given a segment and unblocked This process is repeated until the first task s segment request cannot be satisfied NOTES This directive will cause the calling task to be preempted if one or more local tasks are waiting for a segment and the following conditions exist e a waiting task has a higher priority than the calling task e the size of the segment required by the waiting task is less than or equal to the size of the segment returned 146 RTEMS C User s Guide 14 4 7 REGION_GET_SEGMENT_SIZE Obtain size of a segment CALLING SEQUENCE rtems status code rtems region get segment size rtems id id void segment size t size J DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL segment obtained successfully RTEMS_INVALID_AD
26. 23 Chapter 24 Chapter 25 Chapter 26 11 Signal Manager describes the functionality and directives provided by the Signal Manager Partition Manager describes the functionality and directives pro vided by the Partition Manager Region Manager describes the functionality and directives provided by the Region Manager Dual Ported Memory Manager describes the functionality and di rectives provided by the Dual Ported Memory Manager I O Manager describes the functionality and directives provided by the I O Manager Fatal Error Manager describes the functionality and directives pro vided by the Fatal Error Manager Scheduling Concepts details the RTEMS scheduling algorithm and task state transitions Rate Monotonic Manager describes the functionality and directives provided by the Rate Monotonic Manager Board Support Packages defines the functionality required of user supplied board support packages User Extensions shows the user how to extend RTEMS to incorpo rate custom features Configuring a System details the process by which one tailors RTEMS for a particular single processor or multiprocessor applica tion Multiprocessing Manager presents a conceptual overview of the mul tiprocessing capabilities provided by RTEMS as well as describing the Multiprocessing Communications Interface Layer and Multipro cessing Manager directives Directive Status Codes provides a definition of each of th
27. 5 2 Loosely Coupled Systems 0 ees 202 20 5 8 Systems with Mixed Coupling 2005 203 20 5 4 Heterogeneous Systems 0 00 e eee eee eee ee eee 203 21 User Extensions Manager 205 21 1 IntroductiOnicic s cuve hee eC ORE LORI evt eU 205 21 2 Background bea bor RR Ia RARE anc Eie e 205 21 2 1 Extension Bets cos ty RE eDRERIS ERES GG ERI 205 21 2 2 TCB Extension Area cece ccc ccc ahaa 206 21 2 3 Extensions lieet eta eere per ue E EA ERRE 207 21 2 3 1 TASK CREATE Extension 0000ees 207 21 2 8 2 TASK START Extension 000 00 eee 207 21 2 8 8 TASK RESTART Extension 00065 208 21 2 3 4 TASK DELETE Extension 0005 208 21 2 8 5 TASK SWITCH Extension eeeeeeeess 208 21 2 8 6 TASK BEGIN Extension 0 000 cece eee 209 21 2 3 7 TASK EXITTED Extension 209 21 2 8 8 FATAL Error Extension s eene 209 x RTEMS C User s Guide 21 2 4 Order of Invocation 000 210 21 8 Operations eesriie i e xen eden LR d A d dra 210 21 3 1 Creating an Extension Set 0 0 eee e eee eee 210 21 8 2 Obtaining Extension Set IDs 0 0000 210 21 3 3 Deleting an Extension Set 0 00 cee eee eee eee 211 21 4 jDITGCUlVOS ua sees docs uineiootedleds tea A ERE qud Aiea 211 21 4 1 EXTENSION_CREATE Create a extension set 212 21 4 2 EXTENSION
28. Chapter 5 Task Manager 35 5 3 2 Obtaining Task IDs When a task is created RTEMS generates a unique task ID and assigns it to the created task until it is deleted The task ID may be obtained by either of two methods First as the result of an invocation of the rtems_task_create directive the task ID is stored in a user provided location Second the task ID may be obtained later using the rtems_task_ident directive The task ID is used by other directives to manipulate this task 5 3 3 Starting and Restarting Tasks The rtems_task_start directive is used to place a dormant task in the ready state This enables the task to compete based on its current priority for the processor and other system resources Any actions such as suspension or change of priority performed on a task prior to starting it are nullified when the task is started With the rtems_task_start directive the user specifies the task s starting address and argument The argument is used to communicate some startup information to the task As part of this directive RTEMS initializes the task s stack based upon the task s initial execution mode and start address The starting argument is passed to the task in accordance with the target processor s calling convention The rtems_task_restart directive restarts a task at its initial starting address with its original priority and execution mode but with a possibly different argument The new argument may be used to di
29. Device drivers and defined in C This table may be generated au tomatically for simple applications using only the device drivers that correspond to the following macros e CONFIGURE APPLICATION NEEDS CONSOLE DRIVER e CONFIGURE APPLICATION NEEDS CLOCK DRIVER e CONFIGURE APPLICATION NEEDS TIMER DRIVER e CONFIGURE APPLICATION NEEDS RTC DRIVER e CONFIGURE APPLICATION NEEDS STUB DRIVER Note that network device drivers are not configured in the Device Driver Table 224 Device driver table RTEMS C User s Guide is the address of the Device Driver Table This table contains the entry points for each device driver If the number of device drivers field is zero then this entry should be NULL The format of this table will be discussed below When using the confdefs h mecha nism for configuring an RTEMS application the Device Driver Table is assumed to be named Device drivers and defined in C If the application is providing its own Device Driver Table then the macro CONFIGURE HAS OWN DEVICE DRIVER TABLE must be defined to in dicate this and prevent confdefs h from generating the table number of initial extensions User extension table is the number of initial user extensions There should be the same number of entries as in the User extension table If this field is zero then the User driver address table entry should be NULL When using the confdefs h mechanism for configuring an RT EMS appli cation
30. Events are independent of one another e Events do not hold or transport data e Events are not queued In other words if an event is sent more than once to a task before being received the second and subsequent send operations to that same task have no effect An event set is posted when it is directed or sent to a task A pending event is an event that has been posted but not received An event condition is used to specify the event set which the task desires to receive and the algorithm which will be used to determine when the request is satisfied An event condition is satisfied based upon one of two algorithms which are selected by the user The RTEMS_EVENT_ANY algorithm states that an event condition is satisfied when at least a single requested event is posted The RTEMS_EVENT_ALL algorithm states that an event condition is satisfied when every requested event is posted 11 2 2 Building an Event Set or Condition An event set or condition is built by a bitwise OR of the desired events The set of valid events is RTEMS_EVENT_0 through RTEMS_EVENT_31 If an event is not explicitly specified in the set or condition then it is not present Events are specifically designed to be mutually exclusive therefore bitwise OR and addition operations are equivalent as long as each event appears exactly once in the event set list For example when sending the event set consisting of RTEMS_EVENT_6 RTEMS_EVENT_15 and RTEMS EVENT 31 the event par
31. GET TICKS PER SECOND and the number of ticks since the executive was initialized option is RTEMS CLOCK GET TICKS SINCE BOOT The option argument may taken on any value of the enumerated type rtems clock get options The data type expected for time buffer is based on the value of option as indicated below e RTEMS CLOCK GET TOD rtems time of day e RTEMS CLOCK GET TIME VALUE rtems clock time value e RTEMS CLOCK GET TICKS SINCE BOOT rtems interval e RTEMS CLOCK GET SECONDS SINCE EPOCH rtems interval e RTEMS CLOCK GET TICKS PER SECOND rtems interval NOTES This directive is callable from an ISR This directive will not cause the running task to be preempted Re initializing RTEMS causes the system date and time to be reset to an uninitialized state Another call to rtems_clock_set is required to re initialize the system date and time to application specific specifications 70 RTEMS C User s Guide 7 4 3 CLOCK TICK Announce a clock tick CALLING SEQUENCE rtems status code rtems clock tick void DIRECTIVE STATUS CODES RTEMS SUCCESSFUL clock tick processed successfully DESCRIPTION This directive announces to RTEMS that a system clock tick has occurred The directive is usually called from the timer interrupt ISR of the local processor This directive maintains the system date and time decrements timers for delayed tasks timeouts rate monotonic periods and
32. Message Queue e Event e Signal The semaphore manager supports mutual exclusion involving the synchronization of access to one or more shared user resources Binary semaphores may utilize the optional priority inheritance algorithm to avoid the problem of priority inversion The message manager supports both communication and synchronization while the event manager primarily pro vides a high performance synchronization mechanism The signal manager supports only asynchronous communication and is typically used for exception handling 2 4 Time The development of responsive real time applications requires an understanding of how RTEMS maintains and supports time related operations The basic unit of time in RTEMS is known as a tick The frequency of clock ticks is completely application dependent and determines the granularity and accuracy of all interval and calendar time operations By tracking time in units of ticks RTEMS is capable of supporting interval timing functions such as task delays timeouts timeslicing the delayed execution of timer service routines and the rate monotonic scheduling of tasks An interval is defined as a number of ticks relative to the current time For example when a task delays for an interval of ten ticks it is implied that the task will not execute until ten clock ticks have occurred All intervals are specified using data type rtems_interval A characteristic of interval timing is that the actual interva
33. NULL fatal_extension F More information regarding the user extensions is provided in the User Extensions chapter 22 10 Multiprocessor Configuration Table The Multiprocessor Configuration Table contains information needed when using RTEMS in a multiprocessor configuration Many of the details associated with configuring a mul tiprocessor system are dependent on the multiprocessor communications layer provided by the user The address of the Multiprocessor Configuration Table should be placed in the User_multiprocessing_table entry in the primary Configuration Table Further details regarding many of the entries in the Multiprocessor Configuration Table will be provided in the Multiprocessing chapter When using the confdefs h mechanism for configuring an RTEMS application the macro CONFIGURE_MP_APPLICATION must be defined to automatically generate the Multiprocessor Configuration Table If CONFIGURE_MP_APPLICATION is not defined then a NULL pointer is configured as the address of this table The format of the Multiprocessor Configuration Table is defined in the following C structure typedef struct uint32_t node uint32_t maximum_nodes uint32_t maximum_global_objects uint32_t maximum proxies rtems mpci table User mpci table rtems multiprocessing table node is a unique processor identifier and is used in routing messages be tween nodes in a multiprocessor configuration Each processor must have a unique node
34. Partition Manager 131 13 4 2 PARTITION_IDENT Get ID of a partition CALLING SEQUENCE rtems_status_code rtems_partition_ident rtems_name name uint32_t node rtems id id js DIRECTIVE STATUS CODES RTEMS SUCCESSFUL partition identified successfully RTEMS INVALID ADDRESS id is NULL RTEMS INVALID NAME partition name not found RTEMS INVALID NODE invalid node id DESCRIPTION This directive obtains the partition id associated with the partition name If the partition name is not unique then the partition id will match one of the partitions with that name However this partition id is not guaranteed to correspond to the desired partition The partition id is used with other partition related directives to access the partition NOTES This directive will not cause the running task to be preempted If node is RTEMS SEARCH ALL NODES all nodes are searched with the local node being searched first All other nodes are searched with the lowest numbered node searched first If node is a valid node number which does not represent the local node then only the partitions exported by the designated node are searched This directive does not generate activity on remote nodes It accesses only the local copy of the global object table 132 RTEMS C User s Guide 13 4 3 PARTITION_DELETE Delete a partition CALLING SEQUENCE rtems_status_code rtems_partition_delete rtems_id id DIRECTIVE STATUS CODES
35. When these sections are encountered RTEMS disables all maskable interrupts before the execution of the section and restores them to the previous level upon completion of the section RTEMS has been optimized to insure that interrupts are disabled for a minimum length of time The maximum length of time interrupts are disabled by RTEMS is processor dependent and is detailed in the Timing Specification chapter of the Applications Supplement document for a specific target processor Non maskable interrupts NMI cannot be disabled and ISRs which execute at this level MUST NEVER issue RTEMS system calls If a directive is invoked unpredictable results may occur due to the inability of RTEMS to protect its critical sections However ISRs that make no system calls may safely execute as non maskable interrupts 6 3 Operations 6 3 1 Establishing an ISR The rtems interrupt catch directive establishes an ISR for the system The address of the ISR and its associated CPU vector number are specified to this directive This directive installs the RTEMS interrupt wrapper in the processor s Interrupt Vector Table and the Chapter 6 Interrupt Manager 59 address of the user s ISR in the RTEMS Vector Table This directive returns the previous contents of the specified vector in the RTEMS Vector Table 6 3 2 Directives Allowed from an ISR Using the interrupt manager insures that RTEMS knows when a directive is being called from an ISR The ISR ma
36. a user configurable number of microseconds The current tick expires when the rtems_clock_tick directive is invoked A multiprocessor configuration system which communicates via shared memory An argument provided to a number of directives which determines the maximum length of time an application task is willing to wait to acquire the resource if it is not immediately available An RTEMS object used to invoke subprograms at a later time A data structure associated with each timer used by RTEMS to manage that timer A task scheduling discipline in which tasks of equal priority are exe cuted for a specific period of time before being preempted by another task The application defined unit of time in which the processor is allo cated An acronym for Timer Control Block A temporary rise in system activity which may cause deadlines to be missed Rate Monotonic Scheduling can be used to determine if all deadlines will be met under transient overload Software routines provided by the application to enhance the func tionality of RTEMS A table which contains the entry points for each user extensions User Initialization Tasks Table user provided user supplied vector wait queue yield A table which contains the information needed to create and start each of the user initialization tasks Alternate term for user supplied This term is used to designate any software routines which must be written by the applicati
37. addition operations are equivalent as long as each option appears exactly once in the compo nent list An option listed as a default is not required to appear in the option list although it is a good programming practice to specify default options If all defaults are desired the option RTEMS_DEFAULT_OPTIONS should be specified on this call This example demonstrates the option parameter needed to poll for a segment The option parameter passed to the rtems_region_get_segment directive should be RTEMS_NO_WAIT 14 3 Operations 14 3 1 Creating a Region The rtems_region_create directive creates a region with the user defined name The user may select FIFO or task priority as the method for placing waiting tasks in the task wait queue RTEMS allocates a Region Control Block RNCB from the RNCB free list to maintain the newly created region RTEMS also generates a unique region ID which is returned to the calling task It is not possible to calculate the exact number of bytes available to the user since RTEMS requires overhead for each segment allocated For example a region with one segment that is the size of the entire region has more available bytes than a region with two segments that collectively are the size of the entire region This is because the region with one segment requires only the overhead for one segment while the other region requires the overhead for two segments Due to automatic coalescing the number of segments in the reg
38. allocated buffer could destroy the free buffer chain or the contents of an adjacent allocated buffer 13 2 2 Building a Partition Attribute Set In general an attribute set is built by a bitwise OR of the desired attribute components The set of valid partition attributes is provided in the following table e RTEMS_LOCAL local task default e RTEMS_GLOBAL global task Attribute values are specifically designed to be mutually exclusive therefore bitwise OR and addition operations are equivalent as long as each attribute appears exactly once in the component list An attribute listed as a default is not required to appear in the attribute list although it is a good programming practice to specify default attributes If all defaults are desired the attribute RTEMS_DEFAULT_ATTRIBUTES should be specified on this call The attribute_set parameter should be RTEMS_GLOBAL to indicate that the partition is to be known globally 13 3 Operations 13 3 1 Creating a Partition The rtems_partition_create directive creates a partition with a user specified name The partition s name starting address length and buffer size are all specified to the rtems_partition_create directive RTEMS allocates a Partition Control Block PTCB 128 RTEMS C User s Guide from the PTCB free list This data structure is used by RTEMS to manage the newly created partition The number of buffers in the partition is calculated based upon the spec ified partition le
39. application designer the flexibility to tailor RTEMS to most efficiently meet system requirements while still satisfying even the most stringent memory constraints As a result the size of the RTEMS executive is application dependent A worksheet is pro vided in the Memory Requirements chapter of the Applications Supplement document for a specific target processor The worksheet is used to calculate the memory requirements of a custom RTEMS run time environment The following managers may be optionally excluded e clock e timer e semaphore e message e event e signal e partition e region e dual ported memory e I O e rate monotonic e fatal error e multiprocessing RT EMS utilizes memory for both code and data space Although RTEMS data space must be in RAM its code space can be located in either ROM or RAM 1 9 Audience This manual was written for experienced real time software developers Although some background is provided it is assumed that the reader is familiar with the concepts of task management as well as intertask communication and synchronization Since directives user related data structures and examples are presented in C a basic understanding of the C programming language is required to fully understand the material presented However because of the similarity of the Ada and C RTEMS implementations users will find that the use and behavior of the two implementations is very similar A working knowledge
40. as several independent tasks Although each task will have its own stack and thus separate stack variables they will all share the same static and global variables To make a variable not shareable i e a global variable that is specific to a single task the tasks can call rtems_task_variable_ add to make a separate copy of the variable for each task but all at the same physical address Task variables increase the context switch time to and from the tasks that own them so it is desirable to minimize the number of task variables One efficient method is to have a single task variable that is a pointer to a dynamically allocated structure containing the task s private global data A critical point with per task variables is that each task must separately request that the same global variable is per task private 5 2 9 Building a Task Attribute Set In general an attribute set is built by a bitwise OR of the desired components The set of valid task attribute components is listed below e RTEMS_NO_FLOATING_POINT does not use coprocessor default e RTEMS_FLOATING_POINT uses numeric coprocessor e RTEMS_LOCAL local task default e RTEMS_GLOBAL global task Attribute values are specifically designed to be mutually exclusive therefore bitwise OR and addition operations are equivalent as long as each attribute appears exactly once in the component list A component listed as a default is not required to appear in the componen
41. called in the timer service routine The Timer Server is designed to remain blocked until a task based timer fires This reduces the execution overhead of the Timer Server 8 2 4 Timer Service Routines The timer service routine should adhere to C calling conventions and have a prototype similar to the following rtems timer service routine user routine rtems id timer id void user data J3 Where the timer id parameter is the RTEMS object ID of the timer which is being fired and user_data is a pointer to user defined information which may be utilized by the timer service routine The argument user_data may be NULL 8 3 Operations 8 3 1 Creating a Timer The rtems timer create directive creates a timer by allocating a Timer Control Block TMCB assigning the timer a user specified name and assigning it a timer ID Newly created timers do not have a timer service routine associated with them and are not active 8 3 2 Obtaining Timer IDs When a timer is created RTEMS generates a unique timer ID and assigns it to the created timer until it is deleted The timer ID may be obtained by either of two methods First as the result of an invocation of the rtems timer create directive the timer ID is stored in a user provided location Second the timer ID may be obtained later using the rtems timer ident directive The timer ID is used by other directives to manipulate this timer 8 3 3 Initiating an Interval Timer The rtems ti
42. clock or counter timer device 2 5 Memory Management RTEMS memory management facilities can be grouped into two classes dynamic memory allocation and address translation Dynamic memory allocation is required by applications whose memory requirements vary through the application s course of execution Address translation is needed by applications which share memory with another CPU or an intelli gent Input Output processor The following RTEMS managers provide facilities to manage memory e Region e Partition e Dual Ported Memory RTEMS memory management features allow an application to create simple memory pools of fixed size buffers and or more complex memory pools of variable size segments The partition manager provides directives to manage and maintain pools of fixed size entities such as resource control blocks Alternatively the region manager provides a more general purpose memory allocation scheme that supports variable size blocks of memory which are dynamically obtained and freed by the application The dual ported memory manager provides executive support for address translation between internal and external dual ported RAM address space Chapter 3 RTEMS Data Types 17 3 RTEMS Data Types 3 1 Introduction This chapter contains a complete list of the RTEMS primitive data types in alphabetical order This is intended to be an overview and the user is encouraged to look at the ap propriate chapters in the manual f
43. completion status of the directive RNCB An acronym for Region Control Block round robin A task scheduling discipline in which tasks of equal priority are exe cuted in the order in which they are made ready RS 232 A standard for serial communications 260 running schedule schedulable segments semaphore RTEMS C User s Guide The state of a rate monotonic timer while it is being used to delin eate a period The timer exits this state by either expiring or being canceled The process of choosing which task should next enter the executing state A set of tasks which can be guaranteed to meet their deadlines based upon a specific scheduling algorithm Variable sized memory blocks allocated from a region An RTEMS object which is used to synchronize tasks and provide mutually exclusive access to resources Semaphore Control Block shared memory signal signal set SMCB soft real time system sporadic task stack status code suspend synchronous system call target task Task Control Block A data structure associated with each semaphore used by RTEMS to manage that semaphore Memory which is accessible by multiple nodes in a multiprocessor system An RTEMS provided mechanism to communicate asynchronously with a task Upon reception of a signal the ASR of the receiving task will be invoked A thirty two bit entity which is used to represent a task s collection of pending sign
44. defaults are intentionally set as low as possible By default no application resources are configured The confdefs h file ensures that at least one application tasks or thread is configured and that at least one of the initialization task thread tables is configured The confdefs h file estimates the amount of memory required for the RTEMS Executive Workspace This estimate is only as accurate as the information given to confdefs h 216 RTEMS C User s Guide and may be either too high or too low for a variety of reasons Some of the reasons that confdefs h may reserve too much memory for RTEMS are e All tasks threads are assumed to be floating point Conversely there are many more reasons the resource estimate could be too low e Task thread stacks greater than minimum size must be accounted for explicitly by developer e Memory for messages is not included e Device driver requirements are not included e Network stack requirements are not included e Requirements for add on libraries are not included n general confdefs h is very accurate when given enough information owever it is I l confdefs h te wh h informat H dt quite easy to use a library and not account for its resources The following subsection list all of the constants which can be set by the user 22 2 1 Library Support Definitions This section defines the file system and IO library related configuration parameters sup ported by confdefs h e CONFIGUR
45. defined name The user specifies the maximum message size and maximum number of messages which can be placed in the message queue at one time The user may select FIFO or task priority as the method for placing waiting tasks in the task wait queue RTEMS allocates a Queue Control Block QCB from the QCB free list to maintain the newly created queue as well as memory for the message buffer pool associated with this message queue RTEMS also generates a message queue ID which is returned to the calling task For GLOBAL message queues the maximum message size is effectively limited to the longest message which the MPCI is capable of transmitting 10 3 2 Obtaining Message Queue IDs When a message queue is created RTEMS generates a unique message queue ID The message queue ID may be obtained by either of two methods First as the result of an invocation of the rtems message queue create directive the queue ID is stored in a user provided location Second the queue ID may be obtained later using the rtems message queue ident directive The queue ID is used by other message manager directives to access this message queue Chapter 10 Message Manager 101 10 3 3 Receiving a Message The rtems_message_queue_receive directive attempts to retrieve a message from the specified message queue If at least one message is in the queue then the message is removed from the queue copied to the caller s message buffer and returned immediately alon
46. directives provided by the rate monotonic manager are e rtems_rate_monotonic_create Create a rate monotonic period e rtems_rate_monotonic_ident Get ID of a period e rtems_rate_monotonic_cancel Cancel a period e rtems_rate_monotonic_delete Delete a rate monotonic period e rtems_rate_monotonic_period Conclude current Start next period e rtems_rate_monotonic_get_status Obtain status information on period 19 2 Background The rate monotonic manager provides facilities to manage the execution of periodic tasks This manager was designed to support application designers who utilize the Rate Monotonic Scheduling Algorithm RMS to ensure that their periodic tasks will meet their deadlines even under transient overload conditions Although designed for hard real time systems the services provided by the rate monotonic manager may be used by any application which requires periodic tasks 19 2 1 Rate Monotonic Manager Required Support A clock tick is required to support the functionality provided by this manager 19 2 2 Rate Monotonic Manager Definitions A periodic task is one which must be executed at a regular interval The interval between successive iterations of the task is referred to as its period Periodic tasks can be character ized by the length of their period and execution time The period and execution time of a task can be used to determine the processor utilization for that task Processor utilization is the percenta
47. directories and device nodes and is smaller in executable code size than the full IMFS e STACK CHECKER ON is defined when the application wishes to enable run time stack bounds checking This increases the time required to create tasks as well as adding overhead to each context switch By default this is not defined and thus stack checking is disabled Chapter 22 Configuring a System 217 22 2 2 Basic System Information This section defines the general system configuration parameters supported by confdefs h e CONFIGURE_HAS_OWN_CONFIGURATION_TABLE should only be defined if the applica tion is providing their own complete set of configuration tables e CONFIGURE_INTERRUPT_STACK_MEMORY is set to the size of the interrupt stack The interrupt stack size is usually set by the BSP but since this memory is allocated from the RTEMS Ram Workspace it must be accounted for The default for this field is RTEMS MINIMUM_STACK SIZE NOTE At this time changing this con stant does NOT change the size of the interrupt stack only the amount of memory reserved for it e CONFIGURE EXECUTIVE RAM WORK AREA is the base address of the RTEMS RAM Workspace By default this value is NULL indicating that the BSP is to determine the location of the RTEMS RAM Workspace e CONFIGURE MICROSECONDS PER TICK is the length of time between clock ticks By default this is set to 10000 microseconds e CONFIGURE TICKS PER TIMESLICE is the number of ticks per each tas
48. error status code e Specifying a timeout limits the interval the task will wait before returning with an error status code If the task waits for the segment then it is placed in the region s task wait queue in either FIFO or task priority order All tasks waiting on a region are returned an error when the message queue is deleted 14 3 5 Releasing a Segment When a segment is returned to a region by the rtems_region_return_segment directive it is merged with its unallocated neighbors to form the largest possible segment The first task on the wait queue is examined to determine if its segment request can now be satisfied If so it is given a segment and unblocked This process is repeated until the first task s segment request cannot be satisfied 14 3 6 Obtaining the Size of a Segment The rtems_region_get_segment_size directive returns the size in bytes of the specified segment The size returned includes any extra memory included in the segment because of rounding up to a page size boundary 14 3 7 Changing the Size of a Segment The rtems_region_resize_segment directive is used to change the size in bytes of the specified segment The size may be increased or decreased When increasing the size of a segment it is possible that the request cannot be satisfied This directive is used to support the realloc function in the Standard C Library 14 3 8 Deleting a Region A region can be removed from the system and returned t
49. executive is a small real time operating system used in embedded systems exported An object known by all nodes in a multiprocessor system An object created with the GLOBAL attribute will be exported external address The address used to access dual ported memory by all the nodes in a system which do not own the memory FIFO An acronym for First In First Out First In First Out A discipline for manipulating entries in a data structure floating point coprocessor A component used in computer systems to enhance performance in mathematically intensive situations It is typically viewed as a logical extension of the primary processor freed A resource that has been released by the application to RTEMS global An object that has been created with the GLOBAL attribute and exported to all nodes in a multiprocessor system handler The equivalent of a manager except that it is internal to RTEMS and forms part of the core A handler is a collection of routines which provide a related set of functions For example there is a handler used by RTEMS to manage all objects hard real time system A real time system in which a missed deadline causes the worked performed to have no value or to result in a catastrophic effect on the integrity of the system heap A data structure used to dynamically allocate and deallocate variable sized blocks of memory heterogeneous A multiprocessor computer system composed of dissimilar proces sors homogene
50. features by invoking user supplied extension routines when the following system events occur e Task creation e Task initiation e Task reinitiation e Task deletion e Task context switch e Post task context switch e Task begin e Task exits e Fatal error detection 202 RTEMS C User s Guide User extensions can be used to implement a wide variety of functions including execution profiling non standard coprocessor support debug support and error detection and recov ery For example the context of a non standard numeric coprocessor may be maintained via the user extensions In this example the task creation and deletion extensions are respon sible for allocating and deallocating the context area the task initiation and reinitiation extensions would be responsible for priming the context area and the task context switch extension would save and restore the context of the device For more information on user extensions refer to the User Extensions chapter 20 5 Multiprocessor Communications Interface MPCI RTEMS requires that an MPCI layer be provided when a multiple node application is devel oped This MPCI layer must provide an efficient and reliable communications mechanism between the multiple nodes Tasks on different nodes communicate and synchronize with one another via the MPCI Each MPCI layer must be tailored to support the architecture of the target platform For more information on the MPCI refer to the Multi
51. interval 51 5 4 14 TASK WAKE WHEN Wake up when specified 52 5 4 15 ITERATE_OVER_ALL_THREADS Iterate Over Tasks dap 3A ga XE ae de e eredi pdt adcsua ue E qoe Edad as 53 5 4 16 TASK VARIABLE ADD Associate per task variable 54 5 4 17 TASK VARIABLE GET Obtain value of a per task VOID IO se enae eee ee eee 55 5 4 18 TASK_VARIABLE_DELETE Remove per task variable re 56 6 Interrupt Manager o res eco e enreve ie renes 57 6 1 Introductions 2 cies Eix nekanan pete pei den a a o aiies 57 6 2 Backgroi hd iiie neben eed cde cea E 5 6 2 1 Processing an Interrupt 0 eee eee eee 57 6 2 0 RTEMS Interrupt Levels 0 00 e eee eee 58 6 2 3 Disabling of Interrupts by RTEMS 58 0 3 Operations 5 2046 cee dee a oie Ead S RR Peu bene E uid 58 6 3 1 Establishing an ISR 0 eee 58 6 3 2 Directives Allowed from an ISR 0002 000s 59 6 4 D rectlVveSaososseese ee pem teranmbesd none bes RR REG RR DOR RO eee wees 59 6 4 1 INTERRUPT_CATCH Establish an ISR 60 6 4 3 INTERRUPT DISABLE Disable Interrupts 61 6 4 3 INTERRUPT ENABLE Enable Interrupts 62 6 4 4 INTERRUPT FLASH Flash Interrupts 63 6 4 5 INTERRUPT IS IN PROGRESS Is an ISR in Progress update b eaten pr E a Rita t p Er vo ap ans 64 Clock Manager usecovesz ir adr m hPa Rack 65 Tl Introduccion ui tice ese EO vi ear ERU NE
52. interval ticks clock ticks has passed When the timer fires the timer service routine routine will be invoked with the argument user data NOTES This directive will not cause the running task to be preempted 82 RTEMS C User s Guide 8 4 9 TIMER SERVER FIRE WHEN Fire task based timer when specified CALLING SEQUENCE rtems status code rtems timer server fire when rtems id id rtems time of day wall time rtems timer service routine entry routine void user data DIRECTIVE STATUS CODES RTEMS SUCCESSFUL timer initiated successfully RTEMS INVALID ADDRESS routine is NULL RTEMS INVALID ADDRESS wall time is NULL RTEMS INVALID ID invalid timer id RTEMS NOT DEFINED system date and time is not set RTEMS INVALID CLOCK invalid time of day RTEMS INCORRECT STATE Timer Server not initiated DESCRIPTION This directive initiates the timer specified by id and specifies that when it fires it will be executed by the Timer Server If the timer is running it is automatically canceled before being initiated The timer is scheduled to fire at the time of day specified by wall_time When the timer fires the timer service routine routine will be invoked with the argument user data NOTES This directive will not cause the running task to be preempted Chapter 8 Timer Manager 83 8 4 10 TIMER_RESET Reset an interval timer CALLING SEQUENCE rtems_status_code rtems timer reset rte
53. irssi bonisai 175 18 2 2 Preemption pese eoe a a bte EER 176 18 2 3 Limesliel g 42 oues cope maani eaaa pee e trc 176 18 2 4 Manual Round Robin 0 cece eee eee ee 176 18 2 5 Dispatching Tasks x 2er bets ERE ie A enis 176 18 3 Task State Transitions ssseseeeeeeee e IT 19 Rate Monotonic Manager 181 19 1 Introduction isse RE ER eerie gre aid icm e Ric ica 181 19 2 Background 2 eb e REI E E E 181 19 2 1 Rate Monotonic Manager Required Support 181 19 2 2 Rate Monotonic Manager Definitions 181 19 2 3 Rate Monotonic Scheduling Algorithm 182 19 2 4 Schedulability Analysis sese 182 19 241 AssumiptlOlS li bed ee en RE eaves ee aes 183 19 2 4 2 Processor Utilization Rule 0 22000 183 19 2 4 3 Processor Utilization Rule Example 183 19 2 4 4 First Deadline Rule 0 00 2 eee eee eee 184 19 2 4 5 First Deadline Rule Example 184 19 2 4 6 Relaxation of Assumptions 004 185 19 2 4 7 Further Reading 0 nai nen onnies 185 19 3 Operations eseccutessereergrEERRIRE e e Re E pires 186 19 3 1 Creating a Rate Monotonic Period ssuss 186 19 3 2 Manipulating a Period 0 0 0 186 19 3 3 Obtaining the Status of a Period 005 186 19 34 Canceling a Period ii reete oet tant isa see pk 186 19
54. is the maximum number of ITRON API tasks that can be concurrently active The default is 0 CONFIGURE_MAXIMUM_ITRON_SEMAPHORES is the maximum number of ITRON API semaphores that can be concurrently active The default is 0 CONFIGURE_MAXIMUM_ITRON_EVENTFLAGS is the maximum number of ITRON API eventflags that can be concurrently active The default is 0 CONFIGURE_MAXIMUM_ITRON_MAILBOXES is the maximum number of ITRON API mailboxes that can be concurrently active The default is 0 CONFIGURE_MAXIMUM_ITRON_MESSAGE_BUFFERS is the maximum number of ITRON API message buffers that can be concurrently active The default is 0 CONFIGURE_MAXIMUM_ITRON_PORTS is the maximum number of ITRON API ports that can be concurrently active The default is 0 CONFIGURE_MAXIMUM_ITRON_MEMORY_POOLS is the maximum number of ITRON API memory pools that can be concurrently active The default is 0 CONFIGURE_MAXIMUM_ITRON_FIXED_MEMORY_POOLS is the maximum number of ITRON API fixed memory pools that can be concurrently active The default is 0 22 2 10 ITRON Initialization Task Table Configuration The confdefs h configuration system can automatically generate an ITRON Initializa tion Tasks Table named ITRON_Initialization_tasks with a single entry The following parameters control the generation of that table CONFIGURE_ITRON_INIT_TASK_TABLE is defined if the user wishes to use a ITRON API Initialization Tasks Table The application may choose to use the initial
55. is to avoid the system overhead incurred by the creation of a global message queue When a global message queue is created the message queue s name and id must be transmitted to every node in the system for insertion in the local copy of the global object table 104 RTEMS C User s Guide For GLOBAL message queues the maximum message size is effectively limited to the longest message which the MPCI is capable of transmitting The total number of global objects including message queues is limited by the maxi mum_global_objects field in the configuration table Chapter 10 Message Manager 105 10 4 2 MESSAGE QUEUE IDENT Get ID of a queue CALLING SEQUENCE rtems status code rtems message queue ident rtems name name uint32 t node rtems id id js DIRECTIVE STATUS CODES RTEMS SUCCESSFUL queue identified successfully RTEMS INVALID ADDRESS id is NULL RTEMS INVALID NAME queue name not found RTEMS INVALID NODE invalid node id DESCRIPTION This directive obtains the queue id associated with the queue name specified in name If the queue name is not unique then the queue id will match one of the queues with that name However this queue id is not guaranteed to correspond to the desired queue The queue id is used with other message related directives to access the message queue NOTES This directive will not cause the running task to be preempted If node is RTEMS SEARCH ALL NODES all nodes are se
56. least one A typical initialization task will create and start the static set of application tasks It may also create any other objects used by the application Initialization tasks which only perform initialization should delete themselves upon completion to free resources for other tasks Initialization tasks may transform themselves into a normal application task This transformation typically involves changing priority and execution mode RTEMS does not automatically delete the initialization tasks 4 2 2 The System Initialization Task The System Initialization Task is responsible for initializing all device drivers As a result this task has a higher priority than all other tasks to insure that no application tasks executes until all device drivers are initialized After device initialization in a single processor system this task will delete itself The System Initialization Task must have enough stack space to successfully execute the initialization routines for all device drivers and in multiprocessor configurations the Mul tiprocessor Communications Interface Layer initialization routine The CPU Configuration Table contains a field which allows the application or BSP to increase the default amount of stack space allocated for this task 22 RTEMS C User s Guide In multiprocessor configurations the System Initialization Task does not delete itself after initializing the device drivers Instead it transforms itself into the Mu
57. multipro cessor system a local object table and a global object table The local object table on each node is unique and contains information for all objects created on this node whether those objects are local or global The global object table contains information regarding all global objects in the system and consequently is the same on every node Since each node must maintain an identical copy of the global object table the maximum number of entries in each copy of the table must be the same The maximum number of entries in each copy is determined by the maximum global objects parameter in the Multi processor Configuration Table This parameter as well as the maximum nodes parameter is required to be the same on all nodes To maintain consistency among the table copies every node in the system must be informed of the creation or deletion of a global object 23 2 4 Remote Operations When an application performs an operation on a remote global object RTEMS must gener ate a Remote Request RQ message and send it to the appropriate node After completing the requested operation the remote node will build a Remote Response RR message and send it to the originating node Messages generated as a side effect of a directive such as deleting a global task are known as Remote Processes RP and do not require the receiving node to respond Other than taking slightly longer to execute directives on remote objects the application is un
58. nization 9 2 2 Priority Inversion Priority inversion is a form of indefinite postponement which is common in multitasking preemptive executives with shared resources Priority inversion occurs when a high priority tasks requests access to shared resource which is currently allocated to low priority task The high priority task must block until the low priority task releases the resource This problem is exacerbated when the low priority task is prevented from executing by one or more medium priority tasks Because the low priority task is not executing it cannot complete its interaction with the resource and release that resource The high priority task is effectively prevented from executing by lower priority tasks 9 2 3 Priority Inheritance Priority inheritance is an algorithm that calls for the lower priority task holding a resource to have its priority increased to that of the highest priority task blocked waiting for that resource Each time a task blocks attempting to obtain the resource the task holding the resource may have its priority increased RTEMS supports priority inheritance for local binary semaphores that use the priority task wait queue blocking discipline When a task of higher priority than the task holding the semaphore blocks the priority of the task holding the semaphore is increased to that of the blocking task When the task holding the task completely releases the binary semaphore i e not for a nested release
59. on RTEMS facilities The user initialization task facility is typically used to create the application s set of tasks 20 2 1 Interrupt Stack Requirements The worst case stack usage by interrupt service routines must be taken into account when designing an application If the processor supports interrupt nesting the stack usage must include the deepest nest level The worst case stack usage must account for the following requirements e Processor s interrupt stack frame e Processor s subroutine call stack frame e RTEMS system calls e Registers saved on stack e Application subroutine calls The size of the interrupt stack must be greater than or equal to the constant RTEMS_MINIMUM_STACK_SIZE 20 2 2 Processors with a Separate Interrupt Stack Some processors support a separate stack for interrupts When an interrupt is vectored and the interrupt is not nested the processor will automatically switch from the current stack to the interrupt stack The size of this stack is based solely on the worst case stack usage by interrupt service routines The dedicated interrupt stack for the entire application is supplied and initialized by the reset and initialization code of the user s board support package Since all ISRs use this stack the stack size must take into account the worst case stack usage by any combination of nested ISRs 20 2 3 Processors without a Separate Interrupt Stack Some processors do not support a separate s
60. partition id is used to access the partition with other partition related directives For control and maintenance of the partition RTEMS allocates a PTCB from the local PTCB free pool and initializes it NOTES This directive will not cause the calling task to be preempted The starting address must be properly aligned for the target architecture Th buffer size parameter must be a multiple of the CPU alignment factor Additionally buffer size must be large enough to hold two pointers on the target architecture This is required for RTEMS to manage the buffers when they are free Memory from the partition is not used by RT EMS to store the Partition Control Block The following partition attribute constants are defined by RTEMS e RTEMS LOCAL local task default e RTEMS GLOBAL global task 130 RTEMS C User s Guide The PTCB for a global partition is allocated on the local node The memory space used for the partition must reside in shared memory Partitions should not be made global unless remote tasks must interact with the partition This is to avoid the overhead incurred by the creation of a global partition When a global partition is created the partition s name and id must be transmitted to every node in the system for insertion in the local copy of the global object table The total number of global objects including partitions is limited by the maxi mum_global_objects field in the Configuration Table Chapter 13
61. period 100 RTEMS_TIMEOUT break Perform some periodic actions h missed period so delete period and SELF status rtems rate monotonic delete period if status RTEMS STATUS SUCCESSFUL printf rtems rate monotonic delete failed with status of d n status l exit 1 status rtems_task_delete SELF should not return printf rtems task delete returned with status of d n status exit 1 The above task creates a rate monotonic period as part of its initialization The first time the loop is executed the rtems_rate_monotonic_period directive will initiate the period for 100 ticks and return immediately Subsequent invocations of the rtems_rate_ monotonic_period directive will result in the task blocking for the remainder of the 100 tick period If for any reason the body of the loop takes more than 100 ticks to execute the rtems_rate_monotonic_period directive will return the RTEMS_TIMEOUT status If the above task misses its deadline it will delete the rate monotonic period and itself 19 3 8 Task with Multiple Periods This example consists of a single periodic task which after initialization performs two sets of actions every 100 clock ticks The first set of actions is performed in the first forty clock Chapter 19 Rate Monotonic Manager 189 ticks of every 100 clock ticks while the second set of actions is performed between the fortieth and seventieth clock ti
62. placed at the rear of the queue NOTES The calling task will be preempted if it has preemption enabled and a higher priority task is unblocked as the result of this directive Sending a message to a global message queue which does not reside on the local node will generate a request to the remote node to post the message on the specified message queue If the task to be unblocked resides on a different node from the message queue then the message is forwarded to the appropriate node the waiting task is unblocked and the proxy used to represent the task is reclaimed 108 RTEMS C User s Guide 10 4 5 MESSAGE QUEUE URGENT Put message at front of a queue CALLING SEQUENCE rtems status code rtems message queue urgent rtems id id void buffer size t size Jz DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL message sent successfully RTEMS_INVALID_ID invalid queue id RTEMS_INVALID_SIZE invalid message size RTEMS_INVALID_ADDRESS buffer is NULL RTEMS_UNSATISFIED out of message buffers RTEMS_TOO_MANY queue s limit has been reached DESCRIPTION This directive sends the message buffer of size bytes in length to the queue specified by id If a task is waiting on the queue then the message is copied to the task s buffer and the task is unblocked If no tasks are waiting on the queue then the message is copied to a message buffer which is obtained from this message queue s message buffer pool The message buffer i
63. point operations On some processors it is possible to disable the floating point unit dynamically If this capability is supported by the target processor then RTEMS will utilize this capability to Chapter 5 Task Manager 33 enable the floating point unit only for tasks which are created with the RTEMS_FLOATING_ POINT attribute The consequence of a RTEMS_NO_FLOATING_POINT task attempting to access the floating point unit is CPU dependent but will generally result in an exception condition 5 2 8 Per Task Variables Per task variables are used to support global variables whose value may be unique to a task After indicating that a variable should be treated as private i e per task the task can access and modify the variable but the modifications will not appear to other tasks and other tasks modifications to that variable will not affect the value seen by the task This is accomplished by saving and restoring the variable s value each time a task switch occurs to or from the calling task The value seen by other tasks including those which have not added the variable to their set and are thus accessing the variable as a common location shared among tasks can not be affected by a task once it has added a variable to its local set Changes made to the variable by other tasks will not affect the value seen by a task which has added the variable to its private set This feature can be used when a routine is to be spawned repeatedly
64. priority RTEMS_INVALID_CLOCK invalid time buffer RTEMS_INVALID_NODE invalid node id RTEMS_NOT_CONFIGURED directive not configured RTEMS_NOT_OWNER_OF_RESOURCE not owner of resource RTEMS_NOT_IMPLEMENTED directive not implemented RTEMS_INTERNAL_ERROR RTEMS inconsistency detected RTEMS_NO_MEMORY could not get enough memory 250 RTEMS C User s Guide Chapter 25 Example Application 251 25 Example Application This file contains an example of a simple RTEMS application It instantiates the RTEMS Configuration Information using confdef h and contains two tasks a user initialization task and a simple task This example assumes that a board support package exists include lt rtems h gt rtems_task user_application rtems_task_argument argument rtems_task init_task x rtems task argument ignored rtems id tid rtems status code status rtems name name name rtems build name A P P 1 Status rtems task create name 1 RTEMS MINIMUM STACK SIZE RTEMS NO PREEMPT RTEMS FLOATING POINT amp tid 23 if status RTEMS STATUS SUCCESSFUL 1 printf rtems task create failed with status of d n status exit 1 status rtems_task_start tid user_application 0 if status RTEMS_STATUS_SUCCESSFUL printf rtems task start failed with status of d n status exit 1 status rtems_task_delete SELF
65. produced after a soft deadline may have some value Another distinguishing requirement of real time application systems is the ability to coor dinate or manage a large number of concurrent activities Since software is a synchronous entity this presents special problems One instruction follows another in a repeating syn chronous cycle Even though mechanisms have been developed to allow for the processing of external asynchronous events the software design efforts required to process and manage these events and tasks are growing more complicated The design process is complicated further by spreading this activity over a set of processors instead of a single processor The challenges associated with designing and building real 6 RTEMS C User s Guide time application systems become very complex when multiple processors are involved New requirements such as interprocessor communication channels and global resources that must be shared between competing processors are introduced The ramifications of multiple processors complicate each and every characteristic of a real time system 1 3 Real time Executive Fortunately real time operating systems or real time executives serve as a cornerstone on which to build the application system A real time multitasking executive allows an appli cation to be cast into a set of logical autonomous processes or tasks which become quite manageable Each task is internally synchronous but different tas
66. releasing its resources back to RTEMS before deletion To insure proper deallocation of resources a task should not be deleted unless it is unable to execute or does not hold any RTEMS resources If a task holds RTEMS resources the task should be allowed to deallocate its resources before deletion A task can be directed to release its resources and delete itself by restarting it with a special argument or by sending it a message an event or a signal Deletion of the current task RTEMS SELF will force RTEMS to select another task to execute When a global task is deleted the task id must be transmitted to every node in the system for deletion from the local copy of the global object table The task must reside on the local node even if the task was created with the RTEMS GLOBAL option 44 RTEMS C User s Guide 5 4 6 TASK SUSPEND Suspend a task CALLING SEQUENCE rtems status code rtems task suspend rtems id id 25 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL task restarted successfully RTEMS INVALID ID task id invalid RTEMS ALREADY SUSPENDED task already suspended DESCRIPTION This directive suspends the task specified by id from further execution by placing it in the suspended state T his state is additive to any other blocked state that the task may already be in The task will not execute again until another task issues the rtems task resume directive for this task and any blocked state has been removed
67. rtems_task_get_note rtems_id id uint32_t notepad uint32_t note J DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL note obtained successfully RTEMS_INVALID_ADDRESS note is NULL RTEMS_INVALID_ID invalid task id RTEMS_INVALID_NUMBER invalid notepad location DESCRIPTION This directive returns the note contained in the notepad location of the task specified by id NOTES This directive will not cause the running task to be preempted If id is set to RTEMS_SELF the calling task accesses its own notepad The sixteen notepad locations can be accessed using the constants RTEMS_NOTEPAD_O through RTEMS_NOTEPAD_15 Getting a note of a global task which does not reside on the local node will generate a request to the remote node to obtain the notepad entry of the specified task 50 RTEMS C User s Guide 5 4 12 TASK_SET_NOTE Set task notepad entry CALLING SEQUENCE rtems_status_code rtems_task_set_note rtems_id id uint32_t notepad uint32_t note 33 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL task s note set successfully RTEMS INVALID ID invalid task id RTEMS INVALID NUMBER invalid notepad location DESCRIPTION This directive sets the notepad entry for the task specified by id to the value note NOTES If id is set to RTEMS SELF the calling task accesses its own notepad locations This directive will not cause the running task to be preempted The sixteen notepad locations can be accessed using the co
68. running task to be preempted 214 RTEMS C User s Guide 21 4 3 EXTENSION_DELETE Delete a extension set CALLING SEQUENCE rtems_status_code rtems extension delete rtems id id 25 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL extension set deleted successfully RTEMS INVALID ID invalid extension set id DESCRIPTION This directive deletes the extension set specified by id If the extension set is running it is automatically canceled The ESCB for the deleted extension set is reclaimed by RTEMS NOTES This directive will not cause the running task to be preempted A extension set can be deleted by a task other than the task which created the extension set NOTES This directive will not cause the running task to be preempted Chapter 22 Configuring a System 215 22 Configuring a System 22 1 Introduction RTEMS must be configured for an application This configuration information encompasses a variety of information including the length of each clock tick the maximum number of each RTEMS object that can be created the application initialization tasks and the device drivers in the application This information is placed in data structures that are given to RTEMS at system initialization time This chapter details the format of these data structures as well as a simpler mechanism to automate the generation of these structures 22 2 Automatic Generation of System Configuration RTEMS provides the confdefs h C langua
69. semaphore return SUCCESSFUL When the semaphore cannot be immediately acquired one of the following situations ap plies e By default the calling task will wait forever to acquire the semaphore e Specifying RTEMS_NO_WAIT forces an immediate return with an error status code e Specifying a timeout limits the interval the task will wait before returning with an error status code If the task waits to acquire the semaphore then it is placed in the semaphore s task wait queue in either FIFO or task priority order If the task blocked waiting for a binary semaphore using priority inheritance and the task s priority is greater than that of the task currently holding the semaphore then the holding task will inherit the priority of the blocking task All tasks waiting on a semaphore are returned an error code when the semaphore is deleted When a task successfully obtains a semaphore using priority ceiling and the priority ceiling for this semaphore is greater than that of the holder then the holder s priority will be elevated 9 3 4 Releasing a Semaphore The rtems_semaphore_release directive is used to release the specified semaphore A simplified version of the rtems_semaphore_release directive can be described as follows if no tasks are waiting on this semaphore then increment semaphore s count else assign semaphore to a waiting task return SUCCESSFUL If this is the outermost release of a binary semaphore that uses prio
70. spirts ceritane irani csn 152 rtems_port_internal_to_external 155 rtems_rate_monotonic_cancel 194 rtems rate monotonic create 192 rtems rate monotonic delete 195 rtems rate monotonic get status 197 rtems rate monotonic ident 193 rtems rate monotonic period 196 rtems rate monotonic period status 197 rtems region create sess sss 139 rtems region delete ssssss 141 rtems region extend sss 142 rtems region get segment 143 rtems region get segment size 146 rtems region ident ees 140 rtems region resize segment 147 rtems_region_return_segment 145 rtems_semaphore_create 0000 91 rtems_semaphore_delete 00 94 rtems_semaphore_flush 0 98 rtems_semaphore_ident 04 93 rtems_semaphore_obtain 0 95 rtems_semaphore_release 0 97 rtems shutdown executive 2T rtems signal Catch i 2 1 ll RARE 124 rtems signal send p DPPROY RUE 125 rtems signal Bet D e ERG 18 121 rtems Signed 16 ee eR Rer PROP RerMES 18 rtem s signed32 5 2 62 9 c n I eg RAS ee 18 rtems signed64 ool ls sheets we Ee ree 19 rtems sSigh dB see rre ae eie d ER 18 rtems single ewes Meneame cer 19 rtems st
71. task variable add rtems id tid void task variable void dtor void Mg DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL per task variable added successfully RTEMS_INVALID_ADDRESS task_variable is NULL RTEMS_INVALID_ID invalid task id RTEMS_NO_MEMORY invalid task id RTEMS_ILLEGAL_ON_REMOTE_OBJECT not supported on remote tasks DESCRIPTION This directive adds the memory location specified by the ptr argument to the context of the given task The variable will then be private to the task The task can access and modify the variable but the modifications will not appear to other tasks and other tasks modifications to that variable will not affect the value seen by the task This is accomplished by saving and restoring the variable s value each time a task switch occurs to or from the calling task If the dtor argument is non NULL it specifies the address of a destructor function which will be called when the task is deleted The argument passed to the destructor function is the task s value of the variable NOTES Task variables increase the context switch time to and from the tasks that own them so it is desirable to minimize the number of task variables One efficient method is to have a single task variable that is a pointer to a dynamically allocated structure containing the task s private global data In this case the destructor function could be free Chapter 5 Task Manager 55 5 4 17 TASK
72. the application This configuration parameter is critical as it makes confdefs h configure the resources mutexes and keys used implicitly by the GNAT run time By default this parameter is not defined e CONFIGURE_MAXIMUM_ADA_TASKS is the number of Ada tasks that can be concur rently active in the system By default when CONFIGURE_GNAT_RTEMS is defined this is set to 20 e CONFIGURE_MAXIMUM_FAKE_ADA_TASKS is the number of fake Ada tasks that can be concurrently active in the system A fake Ada task is a non Ada task that makes calls back into Ada code and thus implicitly uses the Ada run time 22 3 Configuration Table The RTEMS Configuration Table is used to tailor an application for its specific needs For example the user can configure the number of device drivers or which APIs may be used The address of the user defined Configuration Table is passed as an argument to the rtems_ initialize_executive directive which MUST be the first RTEMS directive called The RTEMS Configuration Table is defined in the following C structure typedef struct void work space start uint32 t work space size uint32 t maximum extensions uint32 t microseconds per tick uint32 t ticks per timeslice uint32 t maximum devices uint32 t maximum drivers uint32 t number of device drivers rtems driver address table Device driver table uint32 t number of initial extensions rtems extensions table User extension table rtems mu
73. the holder s priority is restored to the value it had before any higher priority was inherited The RTEMS implementation of the priority inheritance algorithm takes into account the scenario in which a task holds more than one binary semaphore The holding task will execute at the priority of the higher of the highest ceiling priority or at the priority of the highest priority task blocked waiting for any of the semaphores the task holds Only when the task releases ALL of the binary semaphores it holds will its priority be restored to the normal value 9 2 4 Priority Ceiling Priority ceiling is an algorithm that calls for the lower priority task holding a resource to have its priority increased to that of the highest priority task which will EVER block waiting for that resource This algorithm addresses the problem of priority inversion although it avoids the possibility of changing the priority of the task holding the resource multiple times The priority ceiling algorithm will only change the priority of the task holding the Chapter 9 Semaphore Manager 87 resource a maximum of one time The ceiling priority is set at creation time and must be the priority of the highest priority task which will ever attempt to acquire that semaphore RTEMS supports priority ceiling for local binary semaphores that use the priority task wait queue blocking discipline When a task of lower priority than the ceiling priority successfully obtains the semapho
74. time Executive cese uere E rekat ee dees 6 1 4 RTEMS Application Architecture 0 cece eee eee eee 6 1 5 RTEMS Internal Architecture 0 00 cee eee T 1 6 User Customization and Extensibility 0 20 0 8 LI Portability gt E 8 18 Memory Requirements sssssseeeeeeee ene 8 1 9 Audience iier erret bh ep der Reg Oba e ido re edd 9 LLOQ Convention S aissar notn iga piinaha ea ae Re haduund ad dad ieee 9 1 11 Manual Organization ssesesesee eee 10 2 Key CONCEDUSs is ceo tuya d ral dO pO ERGO 13 2 1 Introduction phe Der RU ERRARE E ERDEIEE DERE 13 22 ODOC TP 13 2 2 1 Object Nam esac ced che ane Eee n RC RU Recent CR Rn 13 2 2 2 Object IDS ii hebr E eere REPRE RM PROPER 14 2 3 Communication and Synchronization 000 20 00 14 2 4 Times 5 5 tech eee PAP Rod PEE RES ee sales kee 15 2 5 Memory Management 0 cece ia oe eee eee eens 16 3 RTEMS Data Types 17 29 1 Introduction RpreReEerR ERRARE RE TCUOLERE ER bf 32 List of Data Types erba oue Ee e ra PI e Red nada 17 4 Initialization Manager 21 4 L Introduction i pter etd e EE a 21 4 2 Backgrounds i isses re Erben te oie ane T R e ges 21 4 2 1 Initialization Tasks 0 eee 21 4 2 2 The System Initialization Task 00002 eee ee 21 43 3 Whe Idle Vask jeu sree esata dedi ae nees these Pee E RE 22 4 2 4 Initi
75. waiting are remote tasks The calling task does not have to be the task that created the queue although the task and queue must reside on the same node When the queue is deleted any messages in the queue are returned to the free message buffer pool Any information stored in those messages is lost When a global message queue is deleted the message queue id must be transmitted to every node in the system for deletion from the local copy of the global object table Proxies used to represent remote tasks are reclaimed when the message queue is deleted Chapter 10 Message Manager 107 10 4 4 MESSAGE QUEUE SEND Put message at rear of a queue CALLING SEQUENCE rtems status code rtems message queue send rtems id id void buffer size t size Jz DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL message sent successfully RTEMS_INVALID_ID invalid queue id RTEMS_INVALID_SIZE invalid message size RTEMS_INVALID_ADDRESS buffer is NULL RTEMS_UNSATISFIED out of message buffers RTEMS_TOO_MANY queue s limit has been reached DESCRIPTION This directive sends the message buffer of size bytes in length to the queue specified by id If a task is waiting at the queue then the message is copied to the waiting task s buffer and the task is unblocked If no tasks are waiting at the queue then the message is copied to a message buffer which is obtained from this message queue s message buffer pool The message buffer is then
76. 0 9 Operations 446p cete eet aper oce s bbb Adee wae 100 10 3 1 Creating a Message Queue ssesssseeeeeeeeeee 100 10 3 2 Obtaining Message Queue IDs 00 000 eee 100 10 8 8 Receiving a Message eee eee eee ees 101 10 3 4 Sending a Message 0 cece eee eee eee eee 101 10 3 5 Broadcasting a Message 00 cee eee eee eee ee 101 10 3 6 Deleting a Message Queue 0 00 eee eee eee 101 10 4 Directives srepek ea ane wide uals ea oi ccm dts 102 10 4 1 MESSAGE_QUEUE_CREATE Create a queue 103 10 4 2 MESSAGE_QUEUE_IDENT Get ID of a queue 105 10 4 3 MESSAGE QUEUE DELETE Delete a queue 106 10 4 4 MESSAGE QUEUE SEND Put message at rear of a queue rM 107 10 4 5 MESSAGE QUEUE URGENT Put message at front of a queue acest ter e ERE E GE HR CE xe epi 108 10 4 6 MESSAGE QUEUE BROADCAST Broadcast N messages toaqueue ET 109 10 4 7 MESSAGE QUEUE RECEIVE Receive message from a QUCUG PC m 110 10 4 8 MESSAGE QUEUE GET NUMBER PENDING Get number of messages pending on a queue ssusssse 112 10 4 9 MESSAGE QUEUE FLUSH Flush all messages on a DUI MMC nnm 113 Event Manager icscev rer Rer sx ERES 115 Il Introduction e m eter RE RRRRRRRRDEPE REED 115 11 2 Background i4 eire E REC rhe e RD REPRINT 115 11 21 Event Setscsctertbbppe tU UE EM cee dashed bes ons 115 11 2 2 Building an Event Set or Condition
77. 13 Partition Manaber oco eres 127 19 1 Introduction i epo e htt E RRRRIAPP IP RS 127 13 2 Background iti daeomiecend oie EE Ad Rao eque ies 127 13 2 1 Partition Manager Definitions 0000 127 13 2 2 Building a Partition Attribute Set 127 13 3 Operations o2 ermee aee E E EESE EE E EE EE 127 13 3 1 Creating Partition tics srania jeseni aa REPRE ERE I 127 13 3 2 Obtaining Partition IDS rosie kar eisa naken eiiiai kea 128 13 3 3 Acquiring a Buffer oce ee eee RR ern tds 128 13 3 4 Releasing Buffer ascssser dine abe eer Ree 128 13 3 5 Deleting a Partiti seimeni seauni eeen oaa asalt 128 ISA Directivesiic cick esso RR ROI i ne EE a a a E eq 128 13 4 1 PARTITION CREATE Create a partition 129 13 4 2 PARTITION_IDENT Get ID of a partition 131 13 4 3 PARTITION_DELETE Delete a partition 132 13 4 4 PARTITION GET BUFFER Get buffer from a partition HQ 133 13 4 5 PARTITION RETURN BUFFER Return buffer to a Partition izesneseeness edeeeme REG e uer PRATO RA UR Gere ee 134 14 Region Manager e sss 135 DEL JntroduetOn ens Go scene na ten bte pe eda RR ce 135 14 2 Background ee bre HR RR i O i ODE da Ein 135 14 2 1 Region Manager Definitions 00000005 135 14 2 2 Building an Attribute Set 0 0 eee eee eee 135 14 2 3 Building an Option Set 0 cec
78. 3 rtems extensions table 205 rtems fatal error occurred 173 rtems fatal extension 17 209 rtems get claS8S e soe enp di Rus 14 rtems get index cceracecxeca erimus 14 rtems get node suoni stag eR e 14 tenso ranae en a vec bc ESE ES 14 17 rtems initialization tasks table 230 rtems initialize executive 24 rtems initialize executive early 25 rtems_initialize_executive_late 26 rtems interrupt catch ee e nee ences 60 rtems interrupt disable 61 rtems interrupt enable 62 rtems interrupt flash sss 63 rtems interrupt frame sss 17 rtems_interrupt_is_in_progress 64 rtems interrupt level s s 17 rtems interval isiasses eda SERENA 15 18 rtems To GLOSO kesasar iea 033 up pend avers EY ns 167 ptems 10 cOnDtrOlk ie Reo 170 rtems io initialize 163 rtems io lookup name 165 rtems io open e er hd RR AS 166 rtemns lo road essor iena ibed bie RR RE 168 rtems io register driver 161 rtems io register name sss 164 rtems io unregister driver 162 rtems io Write llu el yes WE ES 169 Items l18f 6 v RLIRBMWPRERRIRENUS DINER 18 57 rtems isr entry o ilie n esp a exa 18 rtems iterate over all threads 53 rtems me
79. 3 5 Deleting a Rate Monotonic Period 00 187 19 3 6 Examples ccce sse rre RR n Ernte Qus EERE 187 19 3 7 Simple Periodic Task cocus cien 187 19 3 8 Task with Multiple Periods lssseseeseeeeees 188 19 4 Directives cite dae cde neck eee eee eee 191 19 4 1 RATE MONOTONIC_CREATE Create a rate monotonic jocos RR c 192 19 4 2 RATE MONOTONIC IDENT Get ID of a period 193 19 4 8 RATE MONOTONIC CANCEL Cancel a period 194 19 4 4 RATE MONOTONIC DELETE Delete a rate monotonic je P monde 195 19 4 5 RATE MONOTONIC PERIOD Conclude current Start next PEO cse tese tea EI XT UURPEPEORHR IQ uS 196 19 46 RATE MONOTONIC GET STATUS Obtain status information on period ssssesseseseeeeeeeee 197 20 Board Support Packages 199 20 1 IntroductiOnmnsss eost eben x RU xu Su RE als au ERN RURSUS 199 20 2 Reset and Initialization 0 cece eee ees 199 20 2 1 Interrupt Stack Requirements 00e cece ee ee 200 20 2 2 Processors with a Separate Interrupt Stack 200 20 2 3 Processors without a Separate Interrupt Stack 200 20 3 Device DrIVera8 essere ore becca a hee E eet eens 201 20 3 1 Clock Tick Device Driver 000 es cece nee 201 20 4 User Extensions 0 e eens 201 20 5 Multiprocessor Communications Interface MPCI 202 20 5 4 Tightly Coupled Systems 000 cece 202 20
80. 8 TASK IS SUSPENDED Determine if a task is Suspended CALLING SEQUENCE rtems_status_code rtems_task_is_suspended rtems_id id ve DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL task is NOT suspended RTEMS_ALREADY_SUSPENDED task is currently suspended RTEMS_INVALID_ID task id invalid RTEMS_ILLEGAL_ON_REMOTE_OBJECT not supported on remote tasks DESCRIPTION This directive returns a status code indicating whether or not the specified task is currently suspended NOTES This operation is not currently supported on remote tasks Chapter 5 Task Manager 4T 5 4 9 TASK SET PRIORITY Set task priority CALLING SEQUENCE rtems status code rtems task set priority rtems id id rtems task priority new priority rtems task priority old priority js DIRECTIVE STATUS CODES RTEMS SUCCESSFUL task priority set successfully RTEMS INVALID ID invalid task id RTEMS INVALID ADDRESS invalid return argument pointer RTEMS INVALID PRIORITY invalid task priority DESCRIPTION This directive manipulates the priority of the task specified by id An id of RTEMS SELF is used to indicate the calling task When new priority is not equal to RTEMS CURRENT PRIORITY the specified task s previous priority is returned in old prioritr When new priority is RTEMS CURRENT PRIORITY the specified task s current priority is returned in old priority Valid priorities range from a high of 1 to a low of 255 NOTES The calling task ma
81. ADDRESS invalid address of status DESCRIPTION This directive returns status information associated with the rate monotonic period id in the following data structure typedef struct rtems_rate_monotonic_period_states state uint32_t ticks_since_last_period uint32_t ticks_executed_since_last_period rtems rate monotonic period status If the period s state is RATE MONOTONIC INACTIVE both ticks since last period and ticks executed since last period will be set to 0 Otherwise ticks since last period will contain the number of clock ticks which have occurred since the last in vocation of the rtems rate monotonic period directive Also in this case the ticks executed since last period will indicate how much processor time the owning task has consumed since the invocation of the rtems rate monotonic period directive NOTES This directive will not cause the running task to be preempted 198 RTEMS C User s Guide Chapter 20 Board Support Packages 199 20 Board Support Packages 20 1 Introduction A board support package BSP is a collection of user provided facilities which interface RTEMS and an application with a specific hardware platform These facilities may include hardware initialization device drivers user extensions and a Multiprocessor Communica tions Interface MPCI However a minimal BSP need only support processor reset and initialization and if needed a clock tick 20 2 Reset and Initiali
82. ATTRIBUTES should be specified on this call This example demonstrates the attribute_set parameter needed to create a local message queue with the task priority waiting queue discipline The attribute_set parameter to the rtems_message_queue_create directive could be either RTEMS_PRIORITY or RTEMS_LOCAL RTEMS_PRIORITY The attribute_set parameter can be set to RTEMS_PRIORITY because RTEMS_LOCAL is the default for all created message queues If a similar message queue were to be known globally then the attribute_set parameter would be RTEMS_GLOBAL RTEMS_PRIORITY 10 2 4 Building a MESSAGE_QUEUE_RECEIVE Option Set In general an option is built by a bitwise OR of the desired option components The set of valid options for the rtems_message_queue_receive directive are listed in the following table e RTEMS_WAIT task will wait for a message default e RTEMS_NO_WAIT task should not wait An option listed as a default is not required to appear in the option OR list although it is a good programming practice to specify default options If all defaults are desired the option RTEMS_DEFAULT_OPTIONS should be specified on this call This example demonstrates the option parameter needed to poll for a message to arrive The option parameter passed to the rtems_message_queue_receive directive should be RTEMS_NO_WAIT 10 3 Operations 10 3 1 Creating a Message Queue The rtems_message_queue_create directive creates a message queue with the user
83. Acquire a semaphore e rtems semaphore release Release a semaphore e rtems semaphore flush Unblock all tasks waiting on a semaphore 9 2 Background A semaphore can be viewed as a protected variable whose value can be modified only with the rtems semaphore create rtems semaphore obtain and rtems_semaphore_ release directives RTEMS supports both binary and counting semaphores A binary semaphore is restricted to values of zero or one while a counting semaphore can assume any non negative integer value A binary semaphore can be used to control access to a single resource In particular it can be used to enforce mutual exclusion for a critical section in user code In this instance the semaphore would be created with an initial count of one to indicate that no task is executing the critical section of code Upon entry to the critical section a task must issue the rtems semaphore obtain directive to prevent other tasks from entering the critical section Upon exit from the critical section the task must issue the rtems semaphore release directive to allow another task to execute the critical section A counting semaphore can be used to control access to a pool of two or more resources For example access to three printers could be administered by a semaphore created with an initial count of three When a task requires access to one of the printers it issues the rtems semaphore obtain directive to obtain access to a printer If a print
84. CISC and DSP is planned Since almost all of RTEMS is written in a high level language ports to additional processor families require minimal effort RTEMS multiprocessor support is capable of handling either homogeneous or heterogeneous systems The kernel automatically compensates for architectural differences byte swapping etc between processors This allows a much easier transition from one processor family to another without a major system redesign Since the proposed standards are still in draft form RTEMS cannot and does not claim compliance However the status of the standard is being carefully monitored to guarantee that RTEMS provides the functionality specified in the standard Once approved RTEMS will be made compliant This document is a detailed users guide for a functionally compliant real time multiprocessor executive It describes the user interface and run time behavior of Release 4 7 3 of the C interface to RTEMS RTEMS C User s Guide Chapter 1 Overview 5 1 Overview 1 1 Introduction RTEMS Real Time Executive for Multiprocessor Systems is a real time executive ker nel which provides a high performance environment for embedded military applications including the following features e multitasking capabilities e homogeneous and heterogeneous multiprocessor systems e event driven priority based preemptive scheduling e optional rate monotonic scheduling e intertask communication and synchronizatio
85. CTIVE STATUS CODES RTEMS SUCCESSFUL Timer Server initiated successfully RTEMS TOO MANY too many tasks created DESCRIPTION This directive initiates the Timer Server task This task is responsible for executing all timers initiated via the rtems timer server fire after or rtems timer server fire when directives NOTES This directive could cause the calling task to be preempted The Timer Server task is created using the rtems task create service and must be ac counted for when configuring the system Even through this directive invokes the rtems task create and rtems task start direc tives it should only fail due to resource allocation problems Chapter 8 Timer Manager 81 8 4 8 TIMER_SERVER_FIRE_AFTER Fire task based timer after interval CALLING SEQUENCE rtems_status_code rtems_timer_server_fire_after rtems_id id rtems interval ticks rtems timer service routine entry routine void user data DIRECTIVE STATUS CODES RTEMS SUCCESSFUL timer initiated successfully RTEMS INVALID ADDRESS routine is NULL RTEMS INVALID ID invalid timer id RTEMS INVALID NUMBER invalid interval RTEMS INCORRECT STATE Timer Server not initiated DESCRIPTION This directive initiates the timer specified by id and specifies that when it fires it will be executed by the Timer Server If the timer is running it is automatically canceled before being initiated The timer is scheduled to fire after an
86. Chapter 15 Dual Ported Memory Manager 149 15 Dual Ported Memory Manager 15 1 Introduction The dual ported memory manager provides a mechanism for converting addresses between internal and external representations for multiple dual ported memory areas DPMA The directives provided by the dual ported memory manager are e rtems_port_create Create a port e rtems_port_ident Get ID of a port e rtems_port_delete Delete a port e rtems_port_external_to_internal Convert external to internal address e rtems_port_internal_to_external Convert internal to external address 15 2 Background A dual ported memory area DPMA is an contiguous block of RAM owned by a particular processor but which can be accessed by other processors in the system The owner accesses the memory using internal addresses while other processors must use external addresses RTEMS defines a port as a particular mapping of internal and external addresses There are two system configurations in which dual ported memory is commonly found The first is tightly coupled multiprocessor computer systems where the dual ported memory is shared between all nodes and is used for inter node communication The second configura tion is computer systems with intelligent peripheral controllers These controllers typically utilize the DPMA for high performance data transfers 15 3 Operations 15 3 1 Creating a Port The rtems_port_create directive creates a port into a DPMA w
87. DRESS segment is NULL RTEMS_INVALID_ADDRESS size is NULL RTEMS_INVALID_ID invalid region id RTEMS_INVALID_ADDRESS segment address not in region DESCRIPTION This directive obtains the size in bytes of the specified segment NOTES The actual length of the allocated segment may be larger than the requested size because a segment size is always a multiple of the region s page size Chapter 14 Region Manager 147 14 4 8 REGION RESIZE SEGMENT Change size of a segment CALLING SEQUENCE rtems status code rtems region resize segment rtems id id void segment size t size size t old size DIRECTIVE STATUS CODES RTEMS SUCCESSFUL segment obtained successfully RTEMS INVALID ADDRESS segment is NULL RTEMS INVALID ADDRESS old size is NULL RTEMS INVALID ID invalid region id RTEMS INVALID ADDRESS segment address not in region RTEMS_UNSATISFIED unable to make segment larger DESCRIPTION This directive is used to increase or decrease the size of a segment When increasing the size of a segment it is possible that there is not memory available contiguous to the segment In this case the request is unsatisfied NOTES If an attempt to increase the size of a segment fails then the application may want to allocate a new segment of the desired size copy the contents of the original segment to the new larger segment and then return the original segment 148 RTEMS C User s Guide
88. DRESS task variable is NULL RTEMS ILLEGAL ON REMOTE OBJECT not supported on remote tasks DESCRIPTION This directive removes the given location from a task s context NOTES NONE Chapter 6 Interrupt Manager 57 6 Interrupt Manager 6 1 Introduction Any real time executive must provide a mechanism for quick response to externally gen erated interrupts to satisfy the critical time constraints of the application The interrupt manager provides this mechanism for RTEMS This manager permits quick interrupt re sponse times by providing the critical ability to alter task execution which allows a task to be preempted upon exit from an ISR The interrupt manager includes the following directive e rtems_interrupt_catch Establish an ISR e rtems_interrupt_disable Disable Interrupts e rtems interrupt enable Enable Interrupts e rtems interrupt flash Flash Interrupt e rtems interrupt is in progress Is an ISR in Progress 6 2 Background 6 2 1 Processing an Interrupt The interrupt manager allows the application to connect a function to a hardware inter rupt vector When an interrupt occurs the processor will automatically vector to RT EMS RTEMS saves and restores all registers which are not preserved by the normal C calling convention for the target processor and invokes the user s ISR The user s ISR is respon sible for processing the interrupt clearing the interrupt if necessary and device specific manipulation
89. E LIBIO MAXIMUM FILE DESCRIPTORS is set to the maximum number of files that can be concurrently open Libio requires a Classic RTEMS semaphore for each file descriptor as well as one global one The default value is 3 file descriptors which is enough to support standard input output and error output e CONFIGURE TERMIOS DISABLED is defined if the software implementing POSIX termios functionality is not going to be used by this application By default this is not defined and resources are reserved for the termios functionality e CONFIGURE NUMBER OF TERMIOS PORTS is set to the number of ports using the termios functionality Each concurrently active termios port requires resources By default this is set to 1 so a console port can be used e CONFIGURE HAS OWN MOUNT TABLE is defined when the application provides their own filesystem mount table The mount table is an array of rtems filesystem mount table t entries pointed to by the global variable rtems filesystem mount table The number of entries in this table is in an integer variable named rtems_ filesystem mount table t e CONFIGURE USE IMFS AS BASE FILESYSTEM is defined if the application wishes to use the full functionality IMFS By default the miniIMFS is used The miniIMFS is a minimal functionality subset of the In Memory FileSystem IMFS The miniIMFS is comparable in functionality to the pseudo filesystem name space provided before RTEMS release 4 5 0 The minilMFS supports only
90. EMS_NO_PREEMPT disable preemption e RTEMS_NO_TIMESLICE disable timeslicing default e RTEMS_TIMESLICE enable timeslicing e RTEMS_ASR enable ASR processing default e RTEMS_NO_ASR disable ASR processing e RTEMS_INTERRUPT_LEVEL 0 enable all interrupts default e RTEMS INTERRUPT LEVEL n execute at interrupt level n The interrupt level portion of the task execution mode supports a maximum of 256 interrupt levels These levels are mapped onto the interrupt levels actually supported by the target processor in a processor dependent fashion Tasks should not be made global unless remote tasks must interact with them This avoids the system overhead incurred by the creation of a global task When a global task is created the task s name and id must be transmitted to every node in the system for insertion in the local copy of the global object table The total number of global objects including tasks is limited by the maxi mum global objects field in the Configuration Table 40 RTEMS C User s Guide 5 4 2 TASK_IDENT Get ID of a task CALLING SEQUENCE rtems_status_code rtems_task_ident rtems_name name uint32_t node rtems_id id js DIRECTIVE STATUS CODES RTEMS SUCCESSFUL task identified successfully RTEMS INVALID ADDRESS id is NULL RTEMS INVALID NAME invalid task name RTEMS INVALID NODE invalid node id DESCRIPTION This directive obtains the task id associated with the task n
91. IDENT Get ID of a extension set 213 21 4 8 EXTENSION DELETE Delete a extension set 214 22 Configuring a System 215 22 1 Introduction 2222352 etr bee RR RIA P EE pre 215 22 2 Automatic Generation of System Configuration 215 22 2 1 Library Support Definitions 00000 216 22 2 2 Basic System Information 00 e eee eee eee 217 22 2 3 Device Driver Table 000 cece eee eee eee 217 22 2 4 Multiprocessing Configuration e ee eee 218 22 2 5 Classic API Configuration 0 00 eee eee eee 218 22 2 6 Classic API Initialization Tasks Table Configuration 219 22 2 7 POSIX API Configuration 0 2 eee eene 220 22 2 8 POSIX Initialization Threads Table Configuration 220 22 2 5 ITRON API Configuration 02 nee 220 22 2 10 ITRON Initialization Task Table Configuration 221 22 2 11 Ada Vasks rrin his etr ret habe ee baal 221 22 3 Configuration Table 0 0 es 222 22 4 RTEMS API Configuration Table sees 225 22 5 POSIX API Configuration Table 00 2 e eee 227 22 6 CPU Dependent Information Table 0006 229 22 7 Initialization Task Table 0 eee eee eee 230 22 8 Driver Address Table s ccc c4 ee ces reddite kenad RR eR 2951 22 9 User Extensions Table cece eee kodakan iaa g 232 22 10 Multiprocessor C
92. IGURE_TICKS_PER_TIMESLICE 217 CONFIGURE_USE_IMFS_AS_BASE_FILESYSTEM 216 P posix_api_configuration_table 227 posix_initialization_threads_table 221 R rtems extensions table index 206 rtems addYeSsS iii lied bean ERREUR RR der I7 rtems_api_configuration_table 225 rtemns aSr ios laci des ePRD C Genes 17 123 rtems asr entry ida ed e ee es IT rtems attributes isc stesso ieee cacas 17 rtems boolean d ee ect pe pETING eros 17 rtems build name cece eee 13 rtems Clock get seo sac soe bes 69 rtems clock get options 67 69 264 rtems clock Set eese mene IS Feo bs 68 rtems clock tl6k ag id ere 70 rtems configuration table 222 rtemns cODtext oen sea eer bvpiebeEEiq eds I7 rtems_ context fp skip ersi YT rtems device driver ss IT rtems device driver entry 17 rtems_device_major_number 17 158 rtems_device_minor_number 17 158 rtems double 2 RR I RR VRPEDRR 17 rtems_driver_address_table 231 rtems event receive eese 119 rtems event send cesse 118 rtems event set OE nRa IZ 115 rtems extension sees 17 207 rtems extension create sees 212 rtems extension delete 214 rtems extension ident 21
93. INIT TASK ATTRIBUTES 219 CONFIGURE INIT TASK ENTRY POINT 219 CONFIGURE INIT TASK INITIAL MODES 219 CONFIGURE INIT TASK NAME 219 CONFIGURE INIT TASK PRIORITY 219 CONFIGURE INIT TASK STACK SIZE 219 CONFIGURE INTERRUPT STACK MEMORY 217 CONFIGURE_ITRON_HAS_OWN_INIT_TASK_TABLE ae dana e aaa RE e ONE 221 CONFIGURE_ITRON_INIT_TASK_ATTRIBUTES 221 CONFIGURE_ITRON_INIT_TASK_ENTRY_POINT 221 CONFIGURE_ITRON_INIT_TASK_PRIORITY 221 CONFIGURE_ITRON_INIT_TASK_STACK_SIZE 221 CONFIGURE_ITRON_INIT_TASK_TABLE 221 CONFIGURE_LIBIO_MAXIMUM_FILE_DESCRIPTORS bats E absque E tee ied Gre dis Andean Due ats 216 CONFIGURE MAXIMUM ADA TASKS 222 CONFIGURE MAXIMUM DEVICES s 217 CONFIGURE MAXIMUM DRIVERS 217 CONFIGURE MAXIMUM FAKE ADA TASKS 222 CONFIGURE MAXIMUM ITRON EVENTFLAGS 221 CONFIGURE MAXIMUM ITRON FIXED MEMORY POOLS m 221 CONFIGURE MAXIMUM ITRON MAILBOXES 221 CONFIGURE MAXIMUM ITRON MEMORY POOLS 221 CONFIGURE MAXIMUM ITRON MESSAGE BUFFERS rm 221 CONFIGURE MAXIMUM ITRON PORTS 221 CONFIGURE MAXIMUM ITRON SEMAPHORES 221 CONFIGURE MAXIMUM ITRON TASKS 221 263 CONFIGURE MAXIMUM MESSAGE QUEUES 218 CONFIGURE MAXIMUM PARTITIONS 218 CONFIGURE_MAXIMUM_PERIODS
94. MS_PENDING_EVENTS for the input event condition The pending events are returned to the calling task but the event set is left unaltered 11 3 4 Receiving all Pending Events A task can receive all of the currently pending events by calling the rtems_event_receive directive with a value of RTEMS_ALL_EVENTS for the input event condition and RTEMS_NO_ WAIT RTEMS_EVENT_ANY for the option set The pending events are returned to the calling task and the event set is cleared If no events are pending then the RTEMS_UNSATISFIED status code will be returned 11 4 Directives This section details the event manager s directives A subsection is dedicated to each of this manager s directives and describes the calling sequence related constants usage and status codes 118 RTEMS C User s Guide 11 4 1 EVENT_SEND Send event set to a task CALLING SEQUENCE rtems_status_code rtems_event_send rtems_id id rtems_event_set event_in DIRECTIVE STATUS CODES RTEMS SUCCESSFUL event set sent successfully RTEMS INVALID ID invalid task id DESCRIPTION This directive sends an event set event in to the task specified by id If a blocked task s input event condition is satisfied by this directive then it will be made ready If its input event condition is not satisfied then the events satisfied are updated and the events not satisfied are left pending If the task specified by id is not blocked waiting for events then the eve
95. NCE void rtems_multiprocessing_announce void DIRECTIVE STATUS CODES NONE DESCRIPTION This directive informs RTEMS that a multiprocessing communications packet has arrived from another node This directive is called by the user provided MPCI and is only used in multiprocessor configurations NOTES This directive is typically called from an ISR This directive will almost certainly cause the calling task to be preempted This directive does not generate activity on remote nodes Chapter 24 Directive Status Codes 249 24 Directive Status Codes RTEMS_SUCCESSFUL successful completion RTEMS_TASK_EXITTED returned from a task RTEMS_MP_NOT_CONFIGURED multiprocessing not configured RTEMS_INVALID_NAME invalid object name RTEMS_INVALID_ID invalid object id RTEMS_TOO_MANY too many RTEMS_TIMEOUT timed out waiting RTEMS_OBJECT_WAS_DELETED object was deleted while waiting RTEMS INVALID SIZE invalid specified size RTEMS_INVALID_ADDRESS invalid address specified RTEMS_INVALID_NUMBER number was invalid RTEMS_NOT_DEFINED item not initialized RTEMS_RESOURCE_IN_USE resources outstanding RTEMS_UNSATISFIED request not satisfied RTEMS_INCORRECT_STATE task is in wrong state RTEMS_ALREADY_SUSPENDED task already in state RTEMS_ILLEGAL_ON_SELF illegal for calling task RTEMS_ILLEGAL_ON_REMOTE_OBJECT illegal for remote object RTEMS_CALLED_FROM_ISR invalid environment RTEMS_INVALID_PRIORITY invalid task
96. PPLICATION is not defined the this entry is set to NULL The gen erated table has the name Multiprocessing_configuration RTEMS api configuration is the address of the RTEMS API Configuration Table This table contains information needed by the RTEMS API This field should Chapter 22 Configuring a System 225 be NULL if the RTEMS API is not used NOTE Currently the RTEMS API is required to support support components such as BSPs and libraries which use this API This table is built auto matically and this entry filled in if using the confdefs h applica tion configuration mechanism The generated table has the name Configuration RTEMS API POSIX api configuration is the address of the POSIX API Configuration Table This table contains information needed by the POSIX API This field should be NULL if the POSIX API is not used This table is built automat ically and this entry filled in if using the confdefs h application configuration mechanism The confdefs h application mechanism will fill this field in with the address of the Configuration POSIX API table of POSIX API is configured and NULL if the POSIX API is not configured 22 4 RTEMS API Configuration Table The RTEMS API Configuration Table is used to configure the managers which constitute the RTEMS API for a particular application For example the user can configure the maximum number of tasks for this application The RTEMS API Configuration Table is defined in th
97. PT_LEVEL n execute at interrupt level n The set of default modes may be selected by specifying the RTEMS DEFAULT MODES constant 5 2 6 Accessing Task Arguments All RTEMS tasks are invoked with a single argument which is specified when they are started or restarted The argument is commonly used to communicate startup information to the task The simplest manner in which to define a task which accesses it argument is rtems task user task rtems task argument argument Application tasks requiring more information may view this single argument as an index into an array of parameter blocks 5 2 7 Floating Point Considerations Creating a task with the RTEMS FLOATING POINT attribute flag results in additional memory being allocated for the T CB to store the state of the numeric coprocessor during task switches This additional memory is NOT allocated for RTEMS NO FLOATING POINT tasks Saving and restoring the context of a RTEMS FLOATING POINT task takes longer than that of a RTEMS NO FLOATING POINT task because of the relatively large amount of time required for the numeric coprocessor to save or restore its computational state Since RTEMS was designed specifically for embedded military applications which are float ing point intensive the executive is optimized to avoid unnecessarily saving and restoring the state of the numeric coprocessor The state of the numeric coprocessor is only saved when a RTEMS FLOATING POINT t
98. R E Same 65 G2 Background eee rerer rRRHPIER e Ee ERR 65 2 1 Required S pport ionis otn bet rere 65 7 2 2 Time and Date Data Structures 0 eee eee 65 7 2 3 Clock Tick and Timeslicing sseeeeeeeeeeeeesee 66 TA Delassussssces tire ito EE eR op be RD eS apr 66 2794 TIMEOUTS ceu ame e oheae reece ness arene eee Nes 66 1 9 ODePEatlons xo eiue isa ded aute Reb due ta etae ren pode ut 66 7 3 1 Announcing a Tick 0 cect eens 66 3 2 Setting the inier re ex RE d 66 7 3 8 Obtaining the Time ps Ee kn eee eee eens 67 rJ Bon RETI 67 7 4 1 CLOCK_SET Set system date and time 68 7 4 2 CLOCK GET Get system date and time information 69 7 4 3 CLOCK TICK Announce a clock tick 70 Timer Manager oveesxawib exea hada down 71 8 1 Introduction cots cite cs teehee ta Rh tr rea a at aT 71 8 2 Backerounds s ice knees eaa doth ates diaa 71 8 2 1 Required Support 00 cece eee eee ee eens 71 8 2 2 JLIWerS iesesenseesebeb ensis peel kar ee dba e er ecl 71 8 2 9 Timer SerVer ac enses bene ae Tad ate tere demas 71 8 2 4 Timer Service Routines 0 00 cece eee eee eee 72 8 9 Operations eerst sermi ea gi ai E E e deste todd elias e nea 2 83 1 Creating Dern libe ee ur epUEE PE REN te 12 8 9 2 Obtaining Timer IDs ssssessseees ee eee 72 ii iv RTEMS C User s Guide 8 3 3 Initiating an Interval Timer
99. R EE 241 multiprocessing topologies suus 241 Multiprocessor Communications Interface Table Ene 236 Multiprocessor Configuration Table 234 mutual Exclusion erensia 39 eDer ueber res 85 N nodes definition ici cscs esses siete ene 241 O object Dny tiei tirin t hae EE N 14 object ID composition 0 200008 14 Object name uie b trr ep EU RE RELERETS 13 ObJeCbs sis ide eR OP EE RENS YR RA RSEN RE ANA 13 obtain a semaphore e cence eee 95 obtain buffer from partition 133 obtain ID of a partition 000 131 obtain ID of a period 00008 193 obtain ID of port cies mmm 152 obtain ID of a region 0 02 ee 140 obtain ID of a semaphore 0045 93 obtain ID of an extension set sss 213 obtain per task variable 20000 55 obtain status of period 200 197 obtain task mode cerea emet ri 48 obtain task priority 5 eere ees AT obtain the ID of a timer ssseeessss 75 obtain the time of day 00 69 obtaining class from object ID 14 obtaining index from object ID 14 obtaining node from object ID 14 Open a devive sers ter scans err x Rete Rd da 166 P partition attribute set building 127 partition definition see inde 127 DAELIUIODS eee cates Seal tc
100. RECTIVE STATUS CODES NONE DESCRIPTION This directive is called when the board support package has completed its initialization to allow RTEMS to initialize the application environment based upon the information in the Configuration Table CPU Dependent Information Table User Initialization Tasks Table Device Driver Table User Extension Table Multiprocessor Configuration Table and the Multiprocessor Communications Interface MPCI Table This directive returns to the caller after completing the basic RTEMS initialization but before multitasking is initiated The interrupt level in place when the directive is invoked is returned to the caller This interrupt level should be the same one passed to rtems initialize executive late NOTES The application must use only one of the two initialization sequences rtems_initialize_ executive or rtems_initialize_executive_early and rtems_initialize_executive_ late 26 RTEMS C User s Guide 4 4 3 INITIALIZE_EXECUTIVE_LATE Complete Initialization and Start Multitasking CALLING SEQUENCE void rtems_initialize_executive_late rtems_interrupt_level bsp_level 25 DIRECTIVE STATUS CODES NONE DESCRIPTION This directive is called after the rtems initialize executive early directive has been called to complete the RTEMS initialization sequence and initiate multitasking The in terrupt level returned by the rtems initialize executive early directive should be in bsp level and this v
101. RTEMS C User s Guide Edition 4 7 3 for RTEMS 4 7 3 8 August 2008 On Line Applications Research Corporation On Line Applications Research Corporation TEXinfo 2006 10 04 17 COPYRIGHT 1988 2006 On Line Applications Research Corporation OAR The authors have used their best efforts in preparing this material These efforts include the development research and testing of the theories and programs to determine their effectiveness No warranty of any kind expressed or implied with regard to the software or the material contained in this document is provided No liability arising out of the application or use of any product described in this document is assumed The authors reserve the right to revise this material and to make changes from time to time in the content hereof without obligation to notify anyone of such revision or changes The RTEMS Project is hosted at http www rtems com Any inquiries concerning RTEMS its related support components its documentation or any custom services for RTEMS should be directed to the contacts listed on that site A current list of RTEMS Support Providers is at http www rtems com support html Preface 1 Preface In recent years the cost required to develop a software product has increased significantly while the target hardware costs have decreased Now a larger portion of money is expended in developing using and maintaining software The trend in computing costs is the com
102. S INVALID ID invalid timer id DESCRIPTION This directive cancels the timer id This timer will be reinitiated by the next invocation of rtems timer reset rtems timer fire after or rtems timer fire when with this id NOTES This directive will not cause the running task to be preempted Chapter 8 Timer Manager 77 8 4 4 TIMER_DELETE Delete a timer CALLING SEQUENCE rtems_status_code rtems timer delete rtems id id DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL timer deleted successfully RTEMS_INVALID_ID invalid timer id DESCRIPTION This directive deletes the timer specified by id If the timer is running it is automatically canceled The TMCB for the deleted timer is reclaimed by RTEMS NOTES This directive will not cause the running task to be preempted A timer can be deleted by a task other than the task which created the timer 78 RTEMS C User s Guide 8 4 5 TIMER_FIRE_AFTER Fire timer after interval CALLING SEQUENCE rtems_status_code rtems timer fire after rtems id id rtems interval ticks rtems timer service routine entry routine void user data DIRECTIVE STATUS CODES RTEMS SUCCESSFUL timer initiated successfully RTEMS INVALID ADDRESS routine is NULL RTEMS INVALID ID invalid timer id RTEMS INVALID NUMBER invalid interval DESCRIPTION This directive initiates the timer specified by id If the timer is running it is automatically canceled before being initiated
103. TACKS The starting address of the RTEMS RAM Workspace must be aligned on a four byte bound ary Failure to properly align the workspace area will result in the rtems_fatal_error_ occurred directive being invoked with the RTEMS_INVALID_ADDRESS error code A worksheet is provided in the Memory Requirements chapter of the Applications Supple ment document for a specific target processor to assist the user in calculating the minimum size of the RTEMS RAM Workspace for each application The value calculated with this worksheet is the minimum value that should be specified as the work_space_size parameter of the Configuration Table The allocation of objects can operate in two modes The default mode has an object number ceiling No more than the specified number of objects can be allocated from the RTEMS RAM Workspace The number of objects specified in the particular API Configuration table fields are allocated at initialisation The second mode allows the number of objects to grow to use the available free memory in the RTEMS RAM Workspace The auto extending mode can be enabled individually for each object type by using the macro rtems_resource_unlimited This takes a value as a parameter and is used to set the object maximum number field in an API Configuration table The value is an allocation unit size When RTEMS is required to grow the object table it is grown by this size The kernel will return the object memory back to the RTEMS RAM Workspac
104. TES This directive will not cause the running task to be preempted All buffers begin on a four byte boundary A task cannot wait on a buffer to become available Getting a buffer from a global partition which does not reside on the local node will generate a request telling the remote node to allocate a buffer from the specified partition 134 RTEMS C User s Guide 13 4 5 PARTITION_RETURN_BUFFER Return buffer to a partition CALLING SEQUENCE rtems_status_code rtems_partition_return_buffer rtems_id id void buffer DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL buffer returned successfully RTEMS_INVALID_ADDRESS buffer is NULL RTEMS_INVALID_ID invalid partition id RTEMS_INVALID_ADDRESS buffer address not in partition DESCRIPTION This directive returns the buffer specified by buffer to the partition specified by id NOTES This directive will not cause the running task to be preempted Returning a buffer to a global partition which does not reside on the local node will generate a request telling the remote node to return the buffer to the specified partition Chapter 14 Region Manager 135 14 Region Manager 14 1 Introduction The region manager provides facilities to dynamically allocate memory in variable sized units The directives provided by the region manager are e rtems_region_create Create a region e rtems_region_ident Get ID of a region e rtems_region_delete Delete a region e rtems region ext
105. ULL RTEMS_INVALID_ID invalid region id RTEMS_INVALID_ADDRESS invalid address of area to add DESCRIPTION This directive adds the memory which starts at starting_address for length bytes to the region specified by id NOTES This directive will not cause the calling task to be preempted The calling task does not have to be the task that created the region Any local task that knows the region id can extend the region Chapter 14 Region Manager 143 14 4 5 REGION_GET_SEGMENT Get segment from a region CALLING SEQUENCE rtems status code rtems region get segment rtems id id uint32 t size rtems option option set rtems interval timeout void segment DIRECTIVE STATUS CODES RTEMS SUCCESSFUL segment obtained successfully RTEMS INVALID ADDRESS segment is NULL RTEMS INVALID ID invalid region id RTEMS INVALID SIZE request is for zero bytes or exceeds the size of maximum segment which is possible for this region RTEMS UNSATISFIED segment of requested size not available RTEMS TIMEOUT timed out waiting for segment RTEMS OBJECT WAS DELETED semaphore deleted while waiting e DESCRIPTION This directive obtains a variable size segment from the region specified by id The address of the allocated segment is returned in segment The RTEMS WAIT and RTEMS NO WAIT components of the options parameter are used to specify whether the calling tasks wish to wait for a segment to
106. VARIABLE GET Obtain value of a per task variable CALLING SEQUENCE rtems status code rtems task variable get rtems id tid void task variable void task variable value X DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL per task variable added successfully RTEMS_INVALID_ADDRESS task_variable is NULL RTEMS_INVALID_ADDRESS task_variable_value is NULL RTEMS_INVALID_ADDRESS task_variable is not found RTEMS_NO_MEMORY invalid task id RTEMS_ILLEGAL_ON_REMOTE_OBJECT not supported on remote tasks DESCRIPTION This directive looks up the private value of a task variable for a specified task and stores that value in the location pointed to by the result argument The specified task is usually not the calling task which can get its private value by directly accessing the variable NOTES If you change memory which task_variable_value points to remember to declare that memory as volatile so that the compiler will optimize it correctly In this case both the pointer task_variable_value and data referenced by task_variable_value should be considered volatile 56 RTEMS C User s Guide 5 4 18 TASK VARIABLE DELETE Remove per task variable CALLING SEQUENCE rtems status code rtems task variable delete rtems id tid void task variable DIRECTIVE STATUS CODES RTEMS SUCCESSFUL per task variable added successfully RTEMS INVALID ID invalid task id RTEMS NO MEMORY invalid task id RTEMS INVALID AD
107. _INTERRUPT_MASK and sets inter rupts level n Mode values are specifically designed to be mutually exclusive therefore bitwise OR and ad dition operations are equivalent as long as each mode appears exactly once in the component list A mode component listed as a default is not required to appear in the mode component list although it is a good programming practice to specify default components If all de faults are desired the mode RTEMS DEFAULT MODES and the mask RTEMS ALL MODE MASKS should be used The following example demonstrates the mode and mask parameters used with the rtems task mode directive to place a task at interrupt level 3 and make it non preemptible The mode should be set to RTEMS INTERRUPT LEVEL 3 RTEMS NO PREEMPT to indicate the desired preemption mode and interrupt level while the mask parameter should be set to RTEMS_INTERRUPT_MASK RTEMS NO PREEMPT MASK to indicate that the calling task s interrupt level and preemption mode are being altered 5 3 Operations 5 3 1 Creating Tasks The rtems task create directive creates a task by allocating a task control block assigning the task a user specified name allocating it a stack and floating point context area setting a user specified initial priority setting a user specified initial mode and assigning it a task ID Newly created tasks are initially placed in the dormant state All RT EMS tasks execute in the most privileged mode of the processor
108. _task_restart_extension thread_restart rtems_task_delete_extension thread_delete rtems_task_switch_extension thread_switch rtems_task_begin_extension thread_begin rtems_task_exitted_extension thread_exitted rtems_fatal_extension fatal rtems_extensions_table 206 RTEMS C User s Guide RTEMS allows the user to have multiple extension sets active at the same time First a single static extension set may be defined as the application s User Extension Table which is included as part of the Configuration Table This extension set is active for the entire life of the system and may not be deleted This extension set is especially important because it is the only way the application can provided a FATAL error extension which is invoked if RTEMS fails during the initialize_executive directive The static extension set is optional and may be configured as NULL if no static extension set is required Second the user can install dynamic extensions using the rtems_extension_create di rective These extensions are RTEMS objects in that they have a name an ID and can be dynamically created and deleted In contrast to the static extension set these exten sions can only be created and installed after the initialize executive directive successfully completes execution Dynamic extensions are useful for encapsulating the functionality of an extension set For example the application could use extensions to manage a special coprocessor do perform
109. a comprehensive set of directives to create delete and admin ister tasks The directives provided by the task manager are e rtems_task_create Create a task e rtems_task_ident Get ID of a task e rtems_task_start Start a task e rtems_task_restart Restart a task e rtems_task_delete Delete a task e rtems_task_suspend Suspend a task e rtems_task_resume Resume a task e rtems_task_is_suspended Determine if a task is suspended e rtems_task_set_priority Set task priority e rtems task mode Change current task s mode e rtems task get note Get task notepad entry e rtems task set note Set task notepad entry e rtems task wake after Wake up after interval e rtems task wake when Wake up when specified e rtems iterate over all threads Iterate Over Tasks e rtems task variable add Associate per task variable e rtems task variable get Obtain value of a a per task variable e rtems task variable delete Remove per task variable 5 2 Background 5 2 1 Task Definition Many definitions of a task have been proposed in computer literature Unfortunately none of these definitions encompasses all facets of the concept in a manner which is operating system independent Several of the more common definitions are provided to enable each user to select a definition which best matches their own experience and understanding of the task concept e a dispatchable unit e an entity to which the processor is allocated
110. ackage has completed its initialization to allow RTEMS to initialize the application environment based upon the information in the Configuration Table CPU Dependent Information Table User Initialization Tasks Table Device Driver Table User Extension Table Multiprocessor Configuration Table and the Multiprocessor Communications Interface MPCI Table This directive starts multitasking and does not return to the caller until the rtems_shutdown_executive directive is invoked NOTES This directive MUST be the first RTEMS directive called and it DOES NOT RETURN to the caller until the rtems_shutdown_executive is invoked This directive causes all nodes in the system to verify that certain configuration parameters are the same as those of the local node If an inconsistency is detected then a fatal error is generated The application must use only one of the two initialization sequences rtems_initialize_ executive or rtems_initialize_executive_early and rtems_initialize_executive_ late The rtems_initialize_executive directive is logically equivalent to invoking rtems_initialize_executive_early and rtems_initialize_executive_late with no intervening actions Chapter 4 Initialization Manager 25 4 4 2 INITIALIZE_EXECUTIVE_EARLY Initialize RTEMS and do NOT Start Multitasking CALLING SEQUENCE rtems interrupt level rtems initialize executive early rtems configuration table configuration table rtems cpu table cpu table DI
111. ads structure 22 6 CPU Dependent Information Table The CPU Dependent Information Table is used to describe processor dependent information required by RTEMS This table is generally used to supply RTEMS with information only known by the Board Support Package The contents of this table are discussed in the 230 RTEMS C User s Guide CPU Dependent Information Table chapter of the Applications Supplement document for a specific target processor The confdefs h mechanism does not support generating this table It is normally filled in by the Board Support Package 22 7 Initialization Task Table The Initialization Task Table is used to describe each of the user initialization tasks to the Initialization Manager The table contains one entry for each initialization task the user wishes to create and start The fields of this data structure directly correspond to arguments to the rtems_task_create and rtems_task_start directives The number of entries is found in the number_of_initialization_tasks entry in the Configuration Table The format of each entry in the Initialization Task Table is defined in the following C structure typedef struct rtems_name name size t Stack size rtems task priority initial priority rtems attribute attribute set rtems task entry entry point rtems mode mode set rtems task argument argument rtems initialization tasks table name is the name of this initialization task stack size i
112. ager the timer manager the rate monotonic manager or the timeout option on blocking directives The clock tick is usually provided as an interrupt from a counter timer or a real time clock device When a counter timer is used to provide the clock tick the device is typically programmed to operate in continuous mode This mode selection causes the device to automatically reload the initial count and continue the countdown without programmer intervention This reduces the overhead required to manipulate the counter timer in the clock tick ISR and increases the accuracy of tick occurrences The initial count can be based on the microseconds per tick field in the RTEMS Configuration Table An alternate approach is to set the initial count for a fixed time period such as one millisecond and have the ISR invoke rtems clock tick on the microseconds per tick boundaries Obviously this can induce some error if the configured microseconds per tick is not evenly divisible by the chosen clock interrupt quantum It is important to note that the interval between clock ticks directly impacts the granularity of RTEMS timing operations In addition the frequency of clock ticks is an important factor in the overall level of system overhead A high clock tick frequency results in less processor time being available for task execution due to the increased number of clock tick ISRs 20 4 User Extensions RTEMS allows the application developer to augment selected
113. ailable or the RTEMS NO WAIT option component is set then timeout is ignored NOTES The following semaphore acquisition option constants are defined by RTEMS e RTEMS_WAIT task will wait for semaphore default 96 RTEMS C User s Guide e RTEMS_NO_WAIT task should not wait Attempting to obtain a global semaphore which does not reside on the local node will generate a request to the remote node to access the semaphore If the semaphore is not available and RTEMS_NO_WAIT was not specified then the task must be blocked until the semaphore is released A proxy is allocated on the remote node to represent the task until the semaphore is released A clock tick is required to support the timeout functionality of this directive Chapter 9 Semaphore Manager 97 9 4 5 SEMAPHORE_RELEASE Release a semaphore CALLING SEQUENCE rtems_status_code rtems_semaphore_release rtems_id id 25 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL semaphore released successfully RTEMS INVALID ID invalid semaphore id RTEMS NOT OWNER OF RESOURCE calling task does not own semaphore DESCRIPTION This directive releases the semaphore specified by id The semaphore count is incremented by one If the count is zero or negative then the first task on this semaphore s wait queue is removed and unblocked The unblocked task may preempt the running task if the running task s preemption mode is enabled and the unblocked task has a higher priority
114. al Ofa packet iine oeheeadiias Jagd ee EAA bua Pitas leaded hs 248 24 Directive Status Codes 249 25 Example Application 251 20 GIOSSUEBV cai vusedh Get nacn cess qb vn t ioe dc 253 Command and Variable Index 263 Concept IndeXx i008 saseuwe rte e es 267 xi xii RTEMS C User s Guide
115. alization Manager Failure 0 2000000 22 4 3 Operations i d RI Rpeseteberr ka dad c m reep t ERR d 22 43 1 Initializing RTEMS i iile bre rk tte eene 22 4 83 20 Shutting Down RTEMS seeeeeseeeeeee 23 A A LDurectlves icigee RR RPRercbQEER OE ua pA REED ICE S 23 4 4 1 INITIALIZE_EXECUTIVE Initialize RTEMS 24 4 4 3 INITIALIZE_EXECUTIVE_EARLY Initialize RTEMS and do NOT Start Multitasking 0 0 e eee eee eee 25 ii RTEMS C User s Guide 4 4 83 INITIALIZE_EXECUTIVE_LATE Complete Initialization and Start Multitasking 0 eiiiai eii eee eee 26 4 4 4 SHUTDOWN_EXECUTIVE Shutdown RTEMS 27 D Task MSUSBEODP ess auci sn bod E RE dee Ropa 29 Bul Introduction iiie ie eben erre RICE Eae e oed dne e aiios 29 5 2 Background ii cere pe e Per E REWEE SEE de Ad rs 29 5 2 1 Task Definiti n i terrne riar e yes eee E 29 5 2 2 Task Control Block sseseseeeeeeeeseeeeee 30 5 2 3 Task SbaleB uiis o eri bep x SETS REPE PRISON IE 30 5 244 Task Priority ertet i ose Eee ca 30 5 2 5 Task Mode eet et UR ERE aE E ha 31 5 2 6 Accessing Task Arguments 000 eee eee 32 5 2 7 Floating Point Considerations ee esasen 32 5 2 8 Per Task Variables spcrtosictescenaiacsrai eee eee ees 33 5 2 9 Building a Task Attribute Set 0 cece eee eee 33 5 2 10 Building a Mode and Mask 0 0 cece ee eee 34 5 9 OPeTAtONS errit
116. alled the object index ranges in value from 1 to the maximum number of objects configured for this object type The three components of an object ID make it possible to quickly locate any object in even the most complicated multiprocessor system Object ID s are associated with an object by RTEMS when the object is created and the corresponding ID is returned by the appropriate object create directive The object ID is required as input to all directives involving objects except those which create an object or obtain the ID of an object The object identification directives can be used to dynamically obtain a particular object s ID given its name This mapping is accomplished by searching the name table associated with this object type If the name is non unique then the ID associated with the first occurrence of the name will be returned to the application Since object IDs are returned when the object is created the object identification directives are not necessary in a properly designed single processor application In addition services are provided to portably examine the three subcomponents of an RTEMS ID These services are prototyped as follows uint32_t rtems_get_class rtems_id uint32_t rtems_get_node rtems_id uint32_t rtems_get_index rtems_id An object control block is a data structure defined by RTEMS which contains the infor mation necessary to manage a particular object type For efficiency reasons the format of
117. allows the application designer the flexibility to tailor RTEMS to most efficiently meet system requirements while still satisfying even the most stringent memory constraints As result the size of the RTEMS executive is application dependent A Memory Requirements worksheet is provided in the Applications Supplement document for a specific target processor This worksheet can be used to calculate the memory requirements of a custom RTEMS run time environment To insure that enough memory is allocated for future versions of RTEMS the application designer should round these memory requirements up The following Classic API managers may be optionally excluded e signal e region e dual ported memory e event e multiprocessing e partition e timer e semaphore e message e rate monotonic RTEMS is designed to be built and installed as a library that is linked into the application As such much of RTEMS is implemented in such a way that there is a single entry point per source file This avoids having the linker being forced to pull large object files in their entirety into an application when the application references a single symbol RTEMS based applications must somehow provide memory for RTEMS code and data space Although RTEMS data space must be in RAM its code space can be located in either ROM or RAM In addition the user must allocate RAM for the RTEMS RAM Workspace The size of this area is application dependent and can be
118. als and the signals sent to a task An acronym for Semaphore Control Block A real time system in which a missed deadline does not compromise the integrity of the system A task which executes at irregular intervals and must comply with a hard deadline A minimum period of time between successive itera tions of the task can be guaranteed A data structure that is managed using a Last In First Out LIFO discipline Each task has a stack associated with it which is used to store return information and local variables Also known as error code or return value A term used to describe a task that is not competing for the CPU because it has had a rtems_task_suspend directive Related in order or timing to other occurrences in the system In this document this is used as an alternate term for directive The system on which the application will ultimately execute A logically complete thread of execution The CPU is allocated among the ready tasks A data structure associated with each task used by RTEMS to man age that task Chapter 26 Glossary task switch TCB tick tightly coupled timeout timer Timer Control Block timeslicing timeslice TMCB transient overload user extensions User Extension Table 261 Alternate terminology for context switch Taking control of the pro cessor from one task and given to another An acronym for Task Control Block The basic unit of time used by RTEMS It is
119. alter the basic scheduling algorithm Like preemption timeslicing is specified on a task by task basis using the timeslicing mode flag RTEMS_TIMESLICE_MASK If timeslicing is enabled for a task RTEMS_TIMESLICE then RTEMS will limit the amount of time the task can execute before the processor is allocated to another task Each tick of the real time clock reduces the currently running task s timeslice When the execution time equals the timeslice RTEMS will dispatch another task of the same priority to execute If there are no other tasks of the same priority ready to execute then the current task is allocated an additional timeslice and continues to run Remember that a higher priority task will preempt the task unless preemption is disabled as soon as it is ready to run even if the task has not used up its entire timeslice 18 2 4 Manual Round Robin The final mechanism for altering the RTEMS scheduling algorithm is called manual round robin Manual round robin is invoked by using the rtems_task_wake_after directive with a time interval of RTEMS_YIELD_PROCESSOR This allows a task to give up the processor and be immediately returned to the ready chain at the end of its priority group If no other tasks of the same priority are ready to run then the task does not lose control of the processor 18 2 5 Dispatching Tasks The dispatcher is the RTEMS component responsible for allocating the processor to a ready task In order to allocate th
120. alter the state or length of that period 19 3 4 Canceling a Period The rtems_rate_monotonic_cancel directive is used to stop the period maintained by the specified rate monotonic period The period is stopped and the rate monotonic period can be reinitiated using the rtems_rate_monotonic_period directive Chapter 19 Rate Monotonic Manager 187 19 3 5 Deleting a Rate Monotonic Period The rtems_rate_monotonic_delete directive is used to delete a rate monotonic period If the period is running and has not expired the period is automatically canceled The rate monotonic period s control block is returned to the PCB free list when it is deleted A rate monotonic period can be deleted by a task other than the task which created the period 19 3 6 Examples The following sections illustrate common uses of rate monotonic periods to construct peri odic tasks 19 3 7 Simple Periodic Task This example consists of a single periodic task which after initialization executes every 100 clock ticks 188 RTEMS C User s Guide rtems_task Periodic_task rtems_task_argument arg rtems_name name rtems_id period rtems_status_code status name rtems_build_name P E R D status rtems_rate_monotonic_create name amp period if status RTEMS_STATUS_SUCCESSFUL printf rtems monotonic create failed with status of Ad Nn rc exit 1 while 1 1 if rtems rate monotonic period
121. alue is restored as part of this directive returning to the caller after the rtems shutdown executive directive is invoked NOTES This directive MUST be the second RTEMS directive called and it DOES NOT RETURN to the caller until the rtems shutdown executive is invoked This directive causes all nodes in the system to verify that certain configuration parameters are the same as those of the local node If an inconsistency is detected then a fatal error is generated The application must use only one of the two initialization sequences rtems_initialize_ executive or rtems initialize executive early and rtems initialize executive late Chapter 4 Initialization Manager 27 4 4 4 SHUTDOWN EXECUTIVE Shutdown RTEMS CALLING SEQUENCE void rtems shutdown executive uint32 t result 25 DIRECTIVE STATUS CODES NONE DESCRIPTION This directive is called when the application wishes to shutdown RTEMS and return control to the board support package The board support package resumes execution at the code immediately following the invocation of the rtems initialize executive directive NOTES This directive MUST be the last RTEMS directive invoked by an application and it DOES NOT RETURN to the caller This directive should not be invoked until the executive has successfully completed initial ization 28 RTEMS C User s Guide Chapter 5 Task Manager 29 5 Task Manager 5 1 Introduction The task manager provides
122. ame specified in name A task may obtain its own id by specifying RTEMS SELF or its own task name in name If the task name is not unique then the task id returned will match one of the tasks with that name However this task id is not guaranteed to correspond to the desired task The task id returned in id is used in other task related directives to access the task NOTES This directive will not cause the running task to be preempted If node is RTEMS SEARCH ALL NODES all nodes are searched with the local node being searched first All other nodes are searched with the lowest numbered node searched first If node is a valid node number which does not represent the local node then only the tasks exported by the designated node are searched This directive does not generate activity on remote nodes It accesses only the local copy of the global object table Chapter 5 Task Manager 41 5 4 3 TASK_START Start a task CALLING SEQUENCE rtems_status_code rtems_task_start rtems_id id rtems_task_entry entry_point rtems_task_argument argument js DIRECTIVE STATUS CODES RTEMS SUCCESSFUL ask started successfully RTEMS INVALID ADDRESS invalid task entry point RTEMS INVALID ID invalid task id RTEMS INCORRECT STATE task not in the dormant state RTEMS ILLEGAL ON REMOTE OBJECT cannot start remote task DESCRIPTION This directive readies the task specified by tid for execution based on the prior
123. ameter to the rtems event send directive should be RTEMS EVENT 6 RTEMS EVENT 15 RTEMS EVENT 31 116 RTEMS C User s Guide 11 2 3 Building an EVENT_RECEIVE Option Set In general an option is built by a bitwise OR of the desired option components The set of valid options for the rtems_event_receive directive are listed in the following table e RTEMS_WAIT task will wait for event default e RTEMS_NO_WAIT task should not wait e RTEMS_EVENT_ALL return after all events default e RTEMS_EVENT_ANY return after any events Option values are specifically designed to be mutually exclusive therefore bitwise OR and addition operations are equivalent as long as each option appears exactly once in the compo nent list An option listed as a default is not required to appear in the option list although it is a good programming practice to specify default options If all defaults are desired the option RTEMS_DEFAULT_OPTIONS should be specified on this call This example demonstrates the option parameter needed to poll for all events in a particular event condition to arrive The option parameter passed to the rtems_event_receive direc tive should be either RTEMS_EVENT_ALL RTEMS_NO_WAIT or RTEMS_NO_WAIT The option parameter can be set to RTEMS_NO_WAIT because RTEMS_EVENT_ALL is the default condition for rtems_event_receive 11 3 Operations 11 3 1 Sending an Event Set The rtems_event_send directive allows a task or an ISR t
124. anager avoiding the need to have all drivers statically defined and linked into this table The confdefs h entry CONFIGURE MAXIMUM DRIVERS configures the number of driver slots available to the application 158 RTEMS C User s Guide 16 2 2 Major and Minor Device Numbers Each call to the I O manager must provide a device s major and minor numbers as argu ments The major number is the index of the requested driver s entry points in the Device Driver Table and is used to select a specific device driver The exact usage of the minor number is driver specific but is commonly used to distinguish between a number of devices controlled by the same driver The data types rtems_device_major_number and rtems_device_minor_number are used to manipulate device major and minor numbers respectively 16 2 3 Device Names The I O Manager provides facilities to associate a name with a particular device Directives are provided to register the name of a device and to look up the major minor number pair associated with a device name 16 2 4 Device Driver Environment Application developers as well as device driver developers must be aware of the following regarding the RTEMS I O Manager e A device driver routine executes in the context of the invoking task Thus if the driver blocks the invoking task blocks e The device driver is free to change the modes of the invoking task although the driver should restore them to their original val
125. ance monitoring and to do stack bounds checking Each of these extension sets could be written and installed independently of the others All user extensions are optional and RTEMS places no naming restrictions on the user The user extension entry points are copied into an internal RTEMS structure This means the user does not need to keep the table after creating it and changing the handler entry points dynamically in a table once created has no effect Creating a table local to a function can save space in space limited applications Extension switches do not effect the context switch overhead if no switch handler is installed 21 2 2 TCB Extension Area RTEMS provides for a pointer to a user defined data area for each extension set to be linked to each task s control block This set of pointers is an extension of the TCB and can be used to store additional data required by the user s extension functions It is also possible for a user extension to utilize the notepad locations associated with each task although this may conflict with application usage of those particular notepads The TCB extension is an array of pointers in the TCB The index into the table can be obtained from the extension id returned when the extension is created index rtems get index extension id The number of pointers in the area is the same as the number of user extension sets con figured This allows an application to augment the TCB with user defined in
126. arched with the local node being searched first All other nodes are searched with the lowest numbered node searched first If node is a valid node number which does not represent the local node then only the message queues exported by the designated node are searched This directive does not generate activity on remote nodes It accesses only the local copy of the global object table 106 RTEMS C User s Guide 10 4 3 MESSAGE QUEUE DELETE Delete a queue CALLING SEQUENCE rtems status code rtems message queue delete rtems_id id 25 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL queue deleted successfully RTEMS INVALID ID invalid queue id RTEMS ILLEGAL ON REMOTE OBJECT cannot delete remote queue DESCRIPTION This directive deletes the message queue specified by id As a result of this directive all tasks blocked waiting to receive a message from this queue will be readied and returned a status code which indicates that the message queue was deleted If no tasks are waiting but the queue contains messages then RTEMS returns these message buffers back to the system message buffer pool The QCB for this queue as well as the memory for the message buffers is reclaimed by RTEMS NOTES The calling task will be preempted if its preemption mode is enabled and one or more local tasks with a higher priority than the calling task are waiting on the deleted queue The calling task will NOT be preempted if the tasks that are
127. ariable length buffer where information can be stored to support com munication The length of the message and the information stored in that message are user defined and can be actual data pointer s or empty 10 2 2 Message Queues A message queue permits the passing of messages among tasks and ISRs Message queues can contain a variable number of messages Normally messages are sent to and received from the queue in FIFO order using the rtems_message_queue_send directive However the rtems_message_queue_urgent directive can be used to place messages at the head of a queue in LIFO order Synchronization can be accomplished when a task can wait for a message to arrive at a queue Also a task may poll a queue for the arrival of a message The maximum length message which can be sent is set on a per message queue basis 10 2 3 Building a Message Queue Attribute Set In general an attribute set is built by a bitwise OR of the desired attribute components The set of valid message queue attributes is provided in the following table e RTEMS_FIFO tasks wait by FIFO default e RTEMS_PRIORITY tasks wait by priority e RTEMS_LOCAL local message queue default e RTEMS_GLOBAL global message queue 100 RTEMS C User s Guide An attribute listed as a default is not required to appear in the attribute list although it is a good programming practice to specify default attributes If all defaults are desired the attribute RTEMS_DEFAULT_
128. ask has no effect on the execution state of that task If the task is not the currently running task then the signals are left pending and processed by the task s ASR the next time the task is dispatched to run The ASR is executed immediately before the task is dispatched If the currently running task sends a signal to itself or is sent a signal from an ISR its ASR is immediately dispatched to run provided signal processing is enabled If an ASR with signals enabled is preempted by another task or an ISR and a new signal set is sent then a new copy of the ASR will be invoked nesting the preempted ASR Upon completion of processing the new signal set control will return to the preempted ASR In this situation the ASR must be reentrant Like events identical signals sent to a task are not queued In other words sending the same signal multiple times to a task without any intermediate signal processing occurring for the task has the same result as sending that signal to that task once 12 3 3 Processing an ASR Asynchronous signals were designed to provide the capability to generate software inter rupts The processing of software interrupts parallels that of hardware interrupts As a result the differences between the formats of ASRs and ISRs is limited to the meaning of the single argument passed to an ASR The ASR should have the following calling sequence and adhere to C calling conventions rtems_asr user_routine rtems_signal_s
129. ask is dispatched and that task was not the last task to utilize the coprocessor In a system with only one RTEMS FLOATING POINT task the state of the numeric coprocessor will never be saved or restored Although the overhead imposed by RTEMS FLOATING POINT tasks is minimal some applica tions may wish to completely avoid the overhead associated with RTEMS FLOATING POINT tasks and still utilize a numeric coprocessor By preventing a task from being preempted while performing a sequence of floating point operations a RTEMS NO FLOATING POINT task can utilize the numeric coprocessor without incurring the overhead of a RTEMS FLOATING POINT context switch This approach also avoids the allocation of a floating point context area However if this approach is taken by the application designer NO tasks should be created as RTEMS FLOATING POINT tasks Otherwise the floating point context will not be correctly maintained because RT EMS assumes that the state of the numeric coprocessor will not be altered by RTEMS NO FLOATING POINT tasks If the supported processor type does not have hardware floating capabilities or a standard numeric coprocessor RTEMS will not provide built in support for hardware floating point on that processor In this case all tasks are considered RTEMS NO FLOATING POINT whether created as RTEMS FLOATING POINT or RTEMS NO FLOATING POINT tasks A floating point emulation software library must be utilized for floating
130. ask wait queue by FIFO or task priority is specified Additionally the priority inheritance or priority ceiling algorithm may be selected for local binary semaphores that use the priority task wait queue blocking discipline If the priority ceiling algorithm is selected then the highest priority of any task which will attempt to obtain this semaphore must be specified RTEMS allocates a Semaphore Control Block SMCB from the SMCB free list This data structure is used by RTEMS to manage the newly created semaphore Also a unique semaphore ID is generated and returned to the calling task 9 3 2 Obtaining Semaphore IDs When a semaphore is created RTEMS generates a unique semaphore ID and assigns it to the created semaphore until it is deleted The semaphore ID may be obtained by either of two methods First as the result of an invocation of the rtems_semaphore_create directive the semaphore ID is stored in a user provided location Second the semaphore ID may be obtained later using the rtems_semaphore_ident directive The semaphore ID is used by other semaphore manager directives to access this semaphore 9 3 3 Acquiring a Semaphore The rtems_semaphore_obtain directive is used to acquire the specified semaphore A simplified version of the rtems_semaphore_obtain directive can be described as follows Chapter 9 Semaphore Manager 89 if semaphore s count is greater than zero then decrement semaphore s count else wait for release of
131. asks regardless of priority can be created and started before the initialization deletes itself This technique ensures that all tasks begin to compete for execution time at the same instant when the user initialization task deletes itself 19 2 4 5 First Deadline Rule Example The First Deadline Rule can ensure schedulability even when the Processor Utilization Rule fails The example below is a modification of the Processor Utilization Rule example where task execution time has been increased from 15 to 25 units The following table details the RMS priority period execution time and processor utilization for each task Task RMS Period Execution Processor Priority Time Utilization 1 High 100 25 0 25 2 Medium 200 50 0 25 3 Low 300 100 0 33 The total processor utilization for the modified task set is 0 83 which is above the upper bound of 3 2 1 3 1 or 0 779 imposed by the Processor Utilization Rule Therefore this task set is not guaranteed to be schedulable using RMS However the First Deadline Rule can guarantee the schedulability of this task set This rule calls for one to examine each occurrence of deadline until either all tasks have met their deadline or one task failed to meet its first deadline The following table details the time of each deadline occurrence the maximum number of times each task may have run the total execution time and whether all the deadlines have been met
132. atal error is generated to inform the user that the system is inconsistent When using the confdefs h mechanism for configuring an RTEMS application the value for this field corresponds to the setting of the macro CONFIGURE MP MAXIMUM GLOBAL OBJECTS If not defined by the application then the CONFIGURE MP MAXIMUM GLOBAL OBJECTS macro defaults to the value 32 is the maximum number of proxies which can exist at any given mo ment on this particular node A proxy is a substitute task control block which represent a task residing on a remote node when that task blocks on a remote object Proxies are used in situations in which delayed interaction is required with a remote node When using the confdefs h mechanism for configuring an RTEMS ap plication the value for this field corresponds to the setting of the macro CONFIGURE MP MAXIMUM PROXIES If not defined by the ap plication then the CONFIGURE MP MAXIMUM PROXIES macro defaults to the value 32 is the address of the Multiprocessor Communications Interface Ta ble This table contains the entry points of user provided functions which constitute the multiprocessor communications layer This ta ble must be provided in multiprocessor configurations with all entries configured The format of this table and details regarding its entries can be found in the next section When using the confdefs h mech anism for configuring an RTEMS application the value for this field 236 RTEMS C User
133. atus codes eee ee 19 rtems task i n sdadoeden stad deu i Es 19 32 rtems task argument esses 19 Command and Variable Index rtems_task_begin_extension 19 209 rtems task create eee eee 38 rtems task create extension 19 207 rtems task delete sees 43 rtems task delete extension 19 208 rtems task entry ae e eee EPELE 19 rtems task exitted extension 19 209 rtems task get note ale 49 rtems task ident i oov ESE 40 rtems_task_is_suspended 46 rtems_task_mode priren cece ee 31 48 rtens task priority see e ne 19 30 rtems task restart enn 42 rtems task restart extension 19 208 rtems task resume eese 45 rtems_task_set_note ccc cece eee eee 50 rtems task set priority sess 4T rtems task Start s e el pP PREIFUI 41 rtems task start extension 19 207 rtems task suspend i sorre ririn ira obr EnD 44 rtems_task_switch_extension 19 208 rtems task variable add 54 rtems task variable delete 56 rtems_ rtems_ rtems_ rtems_ rtems_ rtems_ rtems_ rtems_ rtems_ rtems_ rtems_ rtems_ rtems_ rtems_ rtems_ rtems_ rtems_ rtems_ S 265 task variable get sess 55 task wake after dae pirani 51 task wake when ss
134. aware of the location of the objects it acts upon The exact amount of overhead required for a remote operation is dependent on the media connecting the nodes and to a lesser degree on the efficiency of the user provided MPCI routines The following shows the typical transaction sequence during a remote application Chapter 23 Multiprocessing Manager 243 1 The application issues a directive accessing a remote global object 2 RTEMS determines the node on which the object resides 3 RTEMS calls the user provided MPCI routine GET_PACKET to obtain a packet in which to build a RQ message 4 After building a message packet RTEMS calls the user provided MPCI routine SEND_PACKET to transmit the packet to the node on which the object resides referred to as the destination node 5 The calling task is blocked until the RR message arrives and control of the processor is transferred to another task 6 The MPCI layer on the destination node senses the arrival of a packet commonly in an ISR and calls the rtems nultiprocessing announce directive This directive readies the Multiprocessing Server 7 The Multiprocessing Server calls the user provided MPCI routine RE CEIVE PACKET performs the requested operation builds an RR message and returns it to the originating node 8 The MPCI layer on the originating node senses the arrival of a packet typically via an interrupt and calls the RTEMS rtems multiprocessing announce directiv
135. become available or return immediately if no segment is available For either option if a sufficiently sized segment is available then the segment is successfully acquired by returning immediately with the RTEMS SUCCESSFUL status code If the calling task chooses to return immediately and a segment large enough is not avail able then an error code indicating this fact is returned If the calling task chooses to wait for the segment and a segment large enough is not available then the calling task is placed on the region s segment wait queue and blocked If the region was created with the RTEMS PRIORITY option then the calling task is inserted into the wait queue according to its priority However if the region was created with the RTEMS_FIFO option then the calling task is placed at the rear of the wait queue The timeout parameter specifies the maximum interval that a task is willing to wait to obtain a segment If timeout is set to RTEMS NO TIMEOUT then the calling task will wait forever NOTES The actual length of the allocated segment may be larger than the requested size because a segment size is always a multiple of the region s page size The following segment acquisition option constants are defined by RTEMS e RTEMS WAIT task will wait for semaphore default 144 RTEMS C User s Guide e RTEMS_NO_WAIT task should not wait A clock tick is required to support the timeout functionality of this directive Chapter
136. beginning execution user extension handler routine e rtems task create extensionis the entry point for a task creation execution user extension handler routine e rtems task delete extension is the entry point for a task deletion user extension handler routine e rtems task entry is the address of the entry point to an RTEMS ASR It is equiv alent to the entry point of the function implementing the ASR e rtems task exitted extension is the entry point for a task exitted user extension handler routine e rtems task priority is the data type used to manage and manipulate task prior ities e rtems task restart extension is the entry point for a task restart user extension handler routine e rtems task start extension is the entry point for a task start user extension handler routine e rtems task switch extension is the entry point for a task context switch user extension handler routine e rtems tcb is the data structure associated with each task in an RTEMS system e rtems time of day is the data structure used to manage and manipulate calendar time in RTEMS e rtems timer service routine is the return type for an RTEMS Timer Service Routine e rtems timer service routine entry is the address of the entry point to an RTEMS TSR It is equivalent to the entry point of the function implementing the TSR e rtems vector number is the data type used to manage and manipulate interrupt vector numbers 20 RTEMS C User s Guide Chapt
137. calculated using the formula provided in the Memory Requirements chapter of the Applications Supplement document for a specific target processor All private RTEMS data variables and routine names used by RTEMS begin with the underscore _ character followed by an upper case letter If RTEMS is linked with an application then the application code should NOT contain any symbols which begin with 238 RTEMS C User s Guide the underscore character and followed by an upper case letter to avoid any naming conflicts All RTEMS directive names should be treated as reserved words 22 13 Sizing the RTEMS RAM Workspace The RTEMS RAM Workspace is a user specified block of memory reserved for use by RTEMS The application should NOT modify this memory This area consists primarily of the RTEMS data structures whose exact size depends upon the values specified in the Con figuration Table In addition task stacks and floating point context areas are dynamically allocated from the RTEMS RAM Workspace The confdefs h mechanism calcalutes the size of the RTEMS RAM Workspace automati cally It assumes that all tasks are floating point and that all will be allocated the miminum stack space This calculation also automatically includes the memory that will be allocated for internal use by RTEMS The following macros may be set by the application to make the calculation of memory required more accurate e CONFIGURE_MEMORY_OVERHEAD e CONFIGURE_EXTRA_TASK_S
138. cigeseedawewi vada deve keys 32 task attributes building 33 bask Inodescoos secet ee alawtiwaes were EE 31 task mode building c Ade ride ences 34 task priority er naera aE EEEE EE des 30 175 task private data s i6 20 i56 sone rere sis 54 56 task private variable 05 54 56 task Prototypes ener tapas eet 32 task schedulmg 4i cci Ree brne 175 task state transitions 0 sees 177 Cask states sees dates tecch ete dleeeehe ins 30 task definition serce pise dais weve EE RI det 29 TASKS side etadard cone enke teed IPPRNO P B deeds 29 TCB extension area 2 eee eee eee 206 inn doe eitndte aged E Biase Sled Sea eee ARE 15 HIMOCOUUS eR E M doteat weird EEE Cee nen rae 66 nnno c EET yall timesliclIDg bi dese g sainte ce Res Rp RE 31 66 176 U unblock all tasks waiting on a semaphore 98 unlock a semaphore sls eee eee ee 97 unregister a device driver 162 user extensions essen 205 User Extensions Table sss 232 W wake up after an interval 000 51 wake up at a wall time 2000 52 write toa dEVICE ello Meteebdie ewan te 169 270 RTEMS C User s Guide Table of Contents lucro eaanene 1 1 Overview ME m 9 ll JIntroductionz isice sebo eet Rr UR RR PAR EDU YEERPRREIUO 5 1 2 Real time Application Systems ssesseeeseeeleeseeesh 5 1 3 Real
139. cks The last thirty clock ticks are not used by this task 190 RTEMS C User s Guide rtems_task Periodic_task rtems_task_argument arg rtems_name name 1 name 2 rtems id period 1 period 2 rtems status code status name 1 rtems build name P E R 1 D name 2 rtems build name P E R 2 void rtems rate monotonic create name 1 amp period 1 void rtems rate monotonic create name 2 amp period 2 while 1 1 if rtems_rate_monotonic_period period_1 100 TIMEOUT break if rtems_rate_monotonic_period period_2 40 TIMEOUT break Perform first set of actions between clock ticks O and 39 of every 100 ticks if rtems rate monotonic period period 2 30 TIMEOUT break Perform second set of actions between clock 40 and 69 of every 100 ticks THEN Check to make sure we didn t miss the period 2 period if rtems_rate_monotonic_period period 2 STATUS TIMEOUT break void rtems_rate_monotonic_cancel period_2 missed period so delete period and SELF void rtems_rate_monotonic_delete period 1 void rtems rate monotonic delete period 2 void task delete SELF Chapter 19 Rate Monotonic Manager 191 The above task creates two rate monotonic periods as part of its initialization The first time the loop is executed the rtems_rate_monotonic_period directive will i
140. ctive returns to the caller NOTES This directive will not cause the calling task to be preempted 64 RTEMS C User s Guide 6 4 5 INTERRUPT IS IN PROGRESS Is an ISR in Progress CALLING SEQUENCE rtems boolean rtems interrupt is in progress void DIRECTIVE STATUS CODES NONE DESCRIPTION This directive returns TRUE if the processor is currently servicing an interrupt and FALSE otherwise A return value of TRUE indicates that the caller is an interrupt service routine NOT a task The directives available to an interrupt service routine are restricted NOTES This directive will not cause the calling task to be preempted Chapter 7 Clock Manager 65 7 Clock Manager 7 1 Introduction The clock manager provides support for time of day and other time related capabilities The directives provided by the clock manager are e rtems_clock_set Set system date and time e rtems clock get Get system date and time information e rtems clock tick Announce a clock tick 7 2 Background 7 2 1 Required Support For the features provided by the clock manager to be utilized periodic timer interrupts are required Therefore a real time clock or hardware timer is necessary to create the timer interrupts The rtems clock tick directive is normally called by the timer ISR to announce to RTEMS that a system clock tick has occurred Elapsed time is measured in ticks A tick is defined to be an integral number of microseconds whic
141. d size 254 coalesce Configuration Table context context switch control block core CPU critical section CRT deadline device device driver directives dispatch dormant Device Driver Table dual ported embedded envelope RTEMS C User s Guide The process of merging adjacent holes into a single larger hole Some times this process is referred to as garbage collection A table which contains information used to tailor RTEMS for a par ticular application All of the processor registers and operating system data structures associated with a task Alternate term for task switch Taking control of the processor from one task and transferring it to another task A data structure used by the executive to define and control an object When used in this manual this term refers to the internal executive utility functions In the interest of application portability the core of the executive should not be used directly by applications An acronym for Central Processing Unit A section of code which must be executed indivisibly An acronym for Cathode Ray Tube Normally used in reference to the man machine interface A fixed time limit by which a task must have completed a set of actions Beyond this point the results are of reduced value and may even be considered useless or harmful A peripheral used by the application that requires special operation software See also device driver
142. data type used to manage and manipulate RTEMS signal sets with the Signal Manager rtems_signed8 is the data type that corresponds to signed eight bit integers This data type is defined by RTEMS in a manner that ensures it is portable across different target processors rtems signedi6 is the data type that corresponds to signed sixteen bit integers This data type is defined by RT EMS in a manner that ensures it is portable across different target processors Chapter 3 RTEMS Data Types 19 e rtems signed32 is the data type that corresponds to signed thirty two bit integers This data type is defined by RTEMS in a manner that ensures it is portable across different target processors e rtems signed64 is the data type that corresponds to signed sixty four bit integers This data type is defined by RT EMS in a manner that ensures it is portable across different target processors e rtems single is the RTEMS data type that corresponds to single precision floating point on the target hardware e rtems status codes is the e rtems task is the return type for an RTEMS Task e rtems task argument is the data type for the argument passed to each RTEMS task In RT EMS 4 7 and older this is an unsigned thirty two bit integer In RTEMS 4 8 and newer this is based upon the C99 type uintptr t which is guaranteed to be an integer large enough to hold a pointer on the target architecture e rtems task begin extension is the entry point for a task
143. decreased in cost they have become increasingly common in a variety of embedded systems A wide range of custom and general purpose processor boards are based on various thirty two bit processors RTEMS was designed to make no assumptions concerning the characteristics of individual microprocessor families or of specific support hardware In addition RTEMS allows the system developer a high degree of freedom in customizing and extending its features RTEMS assumes the existence of a supported microprocessor and sufficient memory for both RTEMS and the real time application Board dependent components such as clocks interrupt controllers or I O devices can be easily integrated with RTEMS The customiza tion and extensibility features allow RTEMS to efficiently support as many environments as possible 1 7 Portability The issue of portability was the major factor in the creation of RTEMS Since RTEMS is designed to isolate the hardware dependencies in the specific board support packages the real time application should be easily ported to any other processor The use of RTEMS allows the development of real time applications which can be completely independent of a particular microprocessor architecture 1 8 Memory Requirements Since memory is a critical resource in many real time embedded systems RTEMS was specif ically designed to allow unused managers to be excluded from the run time environment Chapter 1 Overview 9 This allows the
144. default 92 RTEMS C User s Guide e RTEMS_INHERIT_PRIORITY use priority inheritance e RTEMS_PRIORITY_CEILING use priority ceiling e RTEMS_NO_PRIORITY_CEILING do not use priority ceiling default e RTEMS_LOCAL local task default e RTEMS_GLOBAL global task Semaphores should not be made global unless remote tasks must interact with the created semaphore This is to avoid the system overhead incurred by the creation of a global semaphore When a global semaphore is created the semaphore s name and id must be transmitted to every node in the system for insertion in the local copy of the global object table The total number of global objects including semaphores is limited by the maxi mum_global_objects field in the Configuration Table Chapter 9 Semaphore Manager 93 9 4 2 SEMAPHORE_IDENT Get ID of a semaphore CALLING SEQUENCE rtems_status_code rtems_semaphore_ident rtems_name name uint32_t node rtems id id js DIRECTIVE STATUS CODES RTEMS SUCCESSFUL semaphore identified successfully RTEMS INVALID NAME semaphore name not found RTEMS INVALID NODE invalid node id DESCRIPTION This directive obtains the semaphore id associated with the semaphore name If the semaphore name is not unique then the semaphore id will match one of the semaphores with that name However this semaphore id is not guaranteed to correspond to the desired semaphore The semaphore id is used by other semapho
145. defined by the user The names used in the examples were arbitrarily chosen and impose no naming conventions on the user 21 2 3 1 TASK CREATE Extension The TASK CREATE extension directly corresponds to the rtems task create directive If this extension is defined in any static or dynamic extension set and a task is being created then the extension routine will automatically be invoked by RTEMS The extension should have a prototype similar to the following boolean user task create rtems tcb current task rtems tcb new task 25 where current task can be used to access the T CB for the currently executing task and new task can be used to access the TCB for the new task being created This exten sion is invoked from the rtems task create directive after new task has been completely initialized but before it is placed on a ready TCB chain The user extension is expected to return the boolean value TRUE if it successfully executed and FALSE otherwise A task create user extension will frequently attempt to allocate resources If this allocation fails then the extension should return FALSE and the entire task create operation will fail 21 2 3 2 TASK START Extension The TASK START extension directly corresponds to the task start directive If this ex tension is defined in any static or dynamic extension set and a task is being started then the extension routine will automatically be invoked by RTEMS The extension should ha
146. directive which is called from the user s real time clock ISR to inform RTEMS that a tick has elapsed The tick frequency value defined in microseconds is a configuration parameter found in the Configuration Table RTEMS divides one million microseconds one second by the number of microseconds per tick to determine the number of calls to the rtems_clock_tick directive per second The frequency of rtems_clock_tick calls determines the resolution granularity for all time dependent RTEMS actions For example calling rtems_clock_tick ten times per second yields a higher resolution than calling rtems_clock_tick two times per second The rtems_clock_ tick directive is responsible for maintaining both calendar time and the dynamic set of timers 7 3 2 Setting the Time The rtems_clock_set directive allows a task or an ISR to set the date and time maintained by RTEMS If setting the date and time causes any outstanding timers to pass their deadline then the expired timers will be fired during the invocation of the rtems_clock_set directive Chapter 7 Clock Manager 67 7 3 3 Obtaining the Time The rtems_clock_get directive allows a task or an ISR to obtain the current date and time or date and time related information The current date and time can be returned in either native or UNIX style format Additionally the application can obtain date and time related information such as the number of seconds since the RTEMS epoch the number of ticks si
147. e This directive readies the Multiprocessing Server 9 The Multiprocessing Server calls the user provided MPCI routine RE CEIVE_PACKET readies the original requesting task and blocks until another packet arrives Control is transferred to the original task which then completes processing of the directive If an uncorrectable error occurs in the user provided MPCI layer the fatal error handler should be invoked RTEMS assumes the reliable transmission and reception of messages by the MPCI and makes no attempt to detect or correct errors 23 2 5 Proxies A proxy is an RTEMS data structure which resides on a remote node and is used to represent a task which must block as part of a remote operation This action can occur as part of the rtems semaphore obtain and rtems message queue receive directives If the object were local the task s control block would be available for modification to indicate it was blocking on a message queue or semaphore However the task s control block resides only on the same node as the task As a result the remote node must allocate a proxy to represent the task until it can be readied The maximum number of proxies is defined in the Multiprocessor Configuration Table Each node in a multiprocessor system may require a different number of proxies to be configured The distribution of proxy control blocks is application dependent and is different from the distribution of tasks 23 2 6 Multiprocessor Configu
148. e The user can specify a specific major device number via the directive s major parameter or let the registration routine find the next available major device number by specifing a major number of 0 The selected major device number is returned via the registered major directive parameter The directive automatically allocation major device numbers from the highest value down This directive automatically invokes the IO INITIALIZE directive if the driver address table has an initialization and open entry The directive returns RTEMS TOO MANY if Device Driver Table is full and RTEMS RESOURCE_IN_USE if a specific major device number is requested and it is al ready in use NOTES The Device Driver Table size is specified in the Configuration Table condiguration This needs to be set to maximum size the application requires 162 RTEMS C User s Guide 16 4 2 IO UNREGISTER DRIVER Unregister a device driver CALLING SEQUENCE rtems status code rtems io unregister driver rtems device major number major 25 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL successfully registered RTEMS INVALID NUMBER invalid major device number DESCRIPTION This directive removes a device driver from the Device Driver Table NOTES Currently no specific checks are made and the driver is not closed Chapter 16 I O Manager 163 16 4 3 IO INITIALIZE Initialize a device driver CALLING SEQUENCE rtems_status_code rtems_io_initialize
149. e 21 Initialization Tasks Table 230 initialize a device driver 0050 163 initialize RTEMS 24 25 26 initiate the Timer Server 000000e 80 install an ASR 2 0 2 4 c0seesseceaae Eus 124 install aii SR 2 ile RR M RMePSEED At d 60 internal addresses definition 149 interrupt level task 0 0 cece eee eee 3l interrupt levels cece eee eee eee eee 58 interrupt processing esses eee eee 5T IO GOofttolz vest uuietePS Mee cr hacen ene 170 IO Manager cs este k metr epRE GR ER REX HERR 157 is interrupt in progress sseeeeeeeeee 64 is task suspended cece eee eee eee 46 ISR vs ASR ciseceganesaiewteadinaeerandaas 121 iterate over all threads 0e eee eee 93 L lock a semaphore 2i lese er doe eee sdanes 95 lookup device major and minor number 165 M major device number 4 158 manual round robin o bere re titt 176 memory management eee DePRPP WI neu 16 message queue attributes 0 99 MESSAGE QUEUES iiildi eI x Re ne eek EPIS 99 IMESSAGCS 22 aei teh Reed thre telah Steed a Geeta 99 minor device number 04 158 MPCI and remote operations 242 MPCI entry points edd ee ere Ree 244 MUPCGI definitioh zz r mm IERI 244 RTEMS C User s Guide Multiprocessing en ir ee eR REV ER
150. e RTEMS TIMESLICE is masked by RTEMS TIMESLICE MASK and enables timeslicing e RTEMS ASR is masked by RTEMS_ASR_MASK and enables ASR processing e RTEMS NO ASR is masked by RTEMS_ASR_MASK and disables ASR processing e RTEMS INTERRUPT LEVEL O is masked by RTEMS INTERRUPT MASK and enables all interrupts e RTEMS INTERRUPT LEVEL n is masked by RTEMS_INTERRUPT_MASK and sets inter rupts level n Chapter 12 Signal Manager 125 12 4 2 SIGNAL_SEND Send signal set to a task CALLING SEQUENCE rtems_status_code rtems_signal_send rtems_id id rtems_signal_set signal_set DIRECTIVE STATUS CODES RTEMS SUCCESSFUL signal sent successfully RTEMS INVALID ID task id invalid RTEMS INVALID NUMBER empty signal set RTEMS NOT DEFINED ASR invalid DESCRIPTION This directive sends a signal set to the task specified in id The signal_set parameter contains the signal set to be sent to the task If a caller sends a signal set to a task with an invalid ASR then an error code is returned to the caller If a caller sends a signal set to a task whose ASR is valid but disabled then the signal set will be caught and left pending for the ASR to process when it is enabled If a caller sends a signal set to a task with an ASR that is both valid and enabled then the signal set is caught and the ASR will execute the next time the task is dispatched to run NOTES Sending a signal set to a task has no effect on that task s sta
151. e directive status codes referenced in this manual Example Application provides a template for simple RTEMS appli cations Glossary defines terms used throughout this manual 12 RTEMS C User s Guide Chapter 2 Key Concepts 13 2 Key Concepts 2 1 Introduction The facilities provided by RTEMS are built upon a foundation of very powerful concepts These concepts must be understood before the application developer can efficiently utilize RTEMS The purpose of this chapter is to familiarize one with these concepts 2 2 Objects RTEMS provides directives which can be used to dynamically create delete and manipulate a set of predefined object types These types include tasks message queues semaphores memory regions memory partitions timers ports and rate monotonic periods The object oriented nature of RTEMS encourages the creation of modular applications built upon re usable building block routines All objects are created on the local node as required by the application and have an RTEMS assigned ID All objects have a user assigned name Although a relationship exists between an object s name and its RTEMS assigned ID the name and ID are not identical Object names are completely arbitrary and selected by the user as a meaningful tag which may commonly reflect the object s use in the application Conversely object IDs are designed to facilitate efficient object manipulation by the executive 2 2 1 Object Na
152. e dynamic extension sets are invoked in the opposite of the order in which they were created followed by the static extension set By invoking the extension sets in this order extensions can be built upon one another At the following system events the extensions are invoked in forward order e Task creation e Task initiation e Task reinitiation e Task deletion e Task context switch e Post task context switch Task begins to execute At the following system events the extensions are invoked in reverse order e Task deletion e Fatal error detection At these system events the extensions are invoked in reverse order to insure that if an extension set is built upon another the more complicated extension is invoked before the extension set it is built upon For example by invoking the static extension set last it is known that the system fatal error extension will be the last fatal error extension executed Another example is use of the task delete extension by the Standard C Library Extension sets which are installed after the Standard C Library will operate correctly even if they utilize the C Library because the C Library s TASK DELETE extension is invoked after that of the other extensions 21 3 Operations 21 3 1 Creating an Extension Set The rtems extension create directive creates and installs an extension set by allocating a Extension Set Control Block ESCB assigning the extension set a user specified name and ass
153. e ee 136 14 3 OperatlOns sentenssa aeaa ia RI EET eR RAPERE 136 14 3 1 Creating a ReglOl 2 e terr b ER RE Ere r3 136 14 3 2 Obtaining Region IDs 0 0 cece eee ees 136 14 3 8 Adding Memory to a Region 00 00 eee eee 137 14 3 4 Acquiring a Segment 00 eee e eee eee ees 137 14 3 5 Releasing a Segment 0 0 cece eee 137 15 16 14 3 6 Obtaining the Size of a Segment 0 2005 137 14 3 7 Changing the Size of a Segment 0 005 137 14 3 8 Deleting a Region seire cece eee eens 137 14 44 Dir ctive8 ise aee cheetahs P YSCOCHH RA 138 14 444 REGION CREATE Create a region 139 14 4 4 REGION IDENT Get ID of a region 140 14 4 58 REGION DELETE Delete a region 141 14 4 4 REGION_EXTEND Add memory to a region 142 14 4 5 REGION GET SEGMENT Get segment from a region TET Paa ea a a a a ean AS 14 4 6 REGION RETURN SEGMENT Return segment to a region 145 14 4 7 REGION GET SEGMEN T SIZE Obtain size of a segment PERI a hones P ikre ie iane iere tieten LAG 14 4 8 REGION RESIZE SEGMENT Change size of a segment pei Wea ad dea a e a aa a E bee Blan RR e t 147 Dual Ported Memory Manager 149 15 1 Introduction 2 pp ecaisdadetinsdsidbia deaseae 149 15 2 Background sescenti eee EERUPEEA RE Tap s 149 15 9 OPETAN ONS sesia ay ia debou
154. e entries are called at critical times in the life of the system and individual tasks The application may create dynamic extensions in addition to this single static set The format of each entry in the User Extensions Table is defined in the following C structure typedef void rtems_extension typedef rtems_extension rtems_task_create_extension Thread_Control executing Thread_Control created typedef rtems extension rtems task delete extension Thread Control executing Thread Control deleted 3 typedef rtems_extension rtems_task_start_extension Thread_Control executing Thread_Control started typedef rtems extension rtems task restart extension Thread Control executing Thread Control restarted 3 typedef rtems_extension rtems_task_switch_extension Thread_Control executing Thread_Control heir 3 typedef rtems_extension rtems_task_begin_extension Thread_Control beginning 3 typedef rtems_extension rtems_task_exitted_extension Thread_Control exiting 3 typedef rtems_extension rtems_fatal_extension Internal_errors_Source the_source boolean is_internal uint32 t the error Chapter 22 Configuring a System 233 E typedef struct rtems_task_create_extension thread_create rtems_task_start_extension thread_start rtems_task_restart_extension thread_restart
155. e following C structure typedef struct uint32_t uint32_t uint32_t uint32_t uint32_t uint32_t uint32_t uint32_t uint32_t uint32_t maximum_tasks maximum_timers maximum semaphores maximum message queues maximum partitions maximum regions maximum ports maximum periods maximum barriers number of initialization tasks rtems initialization tasks table User initialization tasks table rtems api configuration table maximum tasks maximum timers is the maximum number of tasks that can be concurrently active created in the system including initialization tasks When us ing the confdefs h mechanism for configuring an RTEMS applica tion the value for this field corresponds to the setting of the macro CONFIGURE_MAXIMUM_TASKS If not defined by the application then the CONFIGURE_MAXIMUM_TASKS macro defaults to 10 is the maximum number of timers that can be concurrently active in the system When using the confdefs h mechanism for configuring an RTEMS application the value for this field corresponds to the set ting of the macro CONFIGURE_MAXIMUM_TIMERS If not defined by the 226 maximum_semaphores RTEMS C User s Guide application then the CONFIGURE_MAXIMUM_TIMERS macro defaults to 0 is the maximum number of semaphores that can be concurrently ac tive in the system When using the confdefs h mechanism for con figuring an RTEMS application the value for this field corresponds to t
156. e processor to one task it must be deallocated or retrieved from the task currently using it This involves a concept called a context switch To perform a context switch the dispatcher saves the context of the current task and restores the context of the task which has been allocated to the processor Saving and restoring a task s context is the storing loading of all the essential information about a task to enable it to continue Chapter 18 Scheduling Concepts 177 execution without any effects of the interruption For example the contents of a task s register set must be the same when it is given the processor as they were when it was taken away All of the information that must be saved or restored for a context switch is located either in the TCB or on the task s stacks Tasks that utilize a numeric coprocessor and are created with the RTEMS_FLOATING_POINT attribute require additional operations during a context switch These additional operations are necessary to save and restore the floating point context of RTEMS_FLOATING_POINT tasks To avoid unnecessary save and restore operations the state of the numeric coprocessor is only saved when a RTEMS_FLOATING_POINT task is dispatched and that task was not the last task to utilize the coprocessor 18 3 Task State Transitions Tasks in an RTEMS system must always be in one of the five allowable task states These states are executing ready blocked dormant and non existent A task
157. e s must be specified in the mode parameter NOTES The calling task will be preempted if it enables preemption and a higher priority task is ready to run Enabling timeslicing has no effect if preemption is disabled For a task to be timesliced that task must have both preemption and timeslicing enabled A task can obtain its current execution mode without modifying it by calling this directive with a mask value of RTEMS CURRENT MODE To temporarily disable the processing of a valid ASR a task should call this directive with the RTEMS NO ASR indicator specified in mode The set of task mode constants and each mode s corresponding mask constant is provided in the following table e RTEMS PREEMPT is masked by RTEMS PREEMPT MASK and enables preemption e RTEMS NO PREEMPT is masked by RTEMS_PREEMPT_MASK and disables preemption e RTEMS NO TIMESLICE is masked by RTEMS TIMESLICE MASK and disables timeslicing e RTEMS TIMESLICE is masked by RTEMS TIMESLICE MASK and enables timeslicing e RTEMS ASR is masked by RTEMS_ASR_MASK and enables ASR processing e RTEMS NO ASR is masked by RTEMS_ASR_MASK and disables ASR processing e RTEMS INTERRUPT LEVEL O is masked by RTEMS INTERRUPT MASK and enables all interrupts e RTEMS INTERRUPT LEVEL n is masked by RTEMS_INTERRUPT_MASK and sets inter rupts level n Chapter 5 Task Manager 49 5 4 11 TASK_GET_NOTE Get task notepad entry CALLING SEQUENCE rtems_status_code
158. e task s initial execution mode The RTEMS_FLOATING_POINT attribute should be specified if the created task is to use a numeric coprocessor For performance reasons it is recommended that tasks not using the numeric coprocessor should specify the RTEMS_NO_FLOATING_POINT attribute If the RTEMS_GLOBAL attribute is specified the task can be accessed from remote nodes The task id returned in id is used in other task related directives to access the task When created a task is placed in the dormant state and can only be made ready to execute using the directive rtems_task_start NOTES This directive will not cause the calling task to be preempted Valid task priorities range from a high of 1 to a low of 255 If the requested stack size is less than RTEMS_MINIMUM_STACK_SIZE bytes then RTEMS will use RTEMS_MINIMUM_STACK_SIZE as the stack size The value of RTEMS_MINIMUM_STACK_ SIZE is processor dependent Application developers should consider the stack usage of the device drivers when calculating the stack size required for tasks which utilize the driver The following task attribute constants are defined by RTEMS e RTEMS_NO_FLOATING_POINT does not use coprocessor default e RTEMS_FLOATING_POINT uses numeric coprocessor e RTEMS_LOCAL local task default Chapter 5 Task Manager 39 e RTEMS_GLOBAL global task The following task mode constants are defined by RTEMS e RTEMS_PREEMPT enable preemption default e RT
159. e task based a timer after an interval 81 flash 1eterr plisus ice RU RR ER RILEREZ 63 floating point i e caves asa ree RS pLE RE 32 flush a semaphore ssssseeeeeeeeeee 98 flush messages on a queue 0 113 G get buffer from partition 133 get class from object ID 00 14 get ID of a message queue 105 get ID of partition iiec renes 131 get ID of period re Res 193 get ID of port cate iced cs er bre ERAS 152 get ID of region eee RR 140 268 get ID of a semaphore 04 93 get ID ofa tasks sei eee Remb ERES 40 get ID of an extension set 00 213 get index from object ID 06 14 get node from object ID 14 get number of pending messages 112 get per task variable 06 55 get segment from region 143 get size of segment 00008 146 get status of period 06 197 get task mode ence ebore th ER grade 48 get task notepad entry 05 49 get task preemption mode 48 get task prlorky i d REPE es 47 global objects table 0206 242 global objects definition 242 H heterogeneous multiprocessing 246 I initialization tasks 00 eee e eee ee
160. e when an object is destroyed The kernel will only return an allocated block of objects to the RTEMS RAM Workspace if at least half the allocation size of free objects remain allocated RTEMS always keeps one allocation block of objects allocated Here is an example of using rtems_resource_unlimited define CONFIGURE_MAXIMUM_TASKS rtems_resource_unlimited 5 The user is cautioned that future versions of RTEMS may not have the same memory re quirements per object Although the value calculated is suficient for a particular target processor and release of RTEMS memory usage is subject to change across versions and Chapter 22 Configuring a System 239 target processors The user is advised to allocate somewhat more memory than the work sheet recommends to insure compatibility with future releases for a specific target processor and other target processors To avoid problems the user should recalculate the memory requirements each time one of the following events occurs e aconfiguration parameter is modified e task or interrupt stack requirements change e task floating point attribute is altered e RTEMS is upgraded or e the target processor is changed Failure to provide enough space in the RTEMS RAM Workspace will result in the rtems_fatal_error_occurred directive being invoked with the appropriate error code 240 RTEMS C User s Guide Chapter 23 Multiprocessing Manager 241 23 Multiprocessing Manager 23 1 Introduction
161. eates a sleep timer which allows a task to go to sleep for a specified interval The task is blocked until the delay interval has elapsed at which time the task is unblocked A task calling the rtems_task_wake_after directive 36 RTEMS C User s Guide with a delay interval of RTEMS_YIELD_PROCESSOR ticks will yield the processor to any other ready task of equal or greater priority and remain ready to execute The rtems_task_wake_when directive creates a sleep timer which allows a task to go to sleep until a specified date and time The calling task is blocked until the specified date and time has occurred at which time the task is unblocked 5 3 6 Changing Task Priority The rtems_task_set_priority directive is used to obtain or change the current priority of either the calling task or another task If the new priority requested is RTEMS_CURRENT_ PRIORITY or the task s actual priority then the current priority will be returned and the task s priority will remain unchanged If the task s priority is altered then the task will be scheduled according to its new priority The rtems_task_restart directive resets the priority of a task to its original value 5 3 7 Changing Task Mode The rtems_task_mode directive is used to obtain or change the current execution mode of the calling task A task s execution mode is used to enable preemption timeslicing ASR processing and to set the task s interrupt level The rtems_task_restart dir
162. ective resets the mode of a task to its original value 5 3 8 Notepad Locations RTEMS provides sixteen notepad locations for each task Each notepad location may contain a note consisting of four bytes of information RTEMS provides two directives rtems_task_set_note and rtems_task_get_note that enable a user to access and change the notepad locations The rtems_task_set_note directive enables the user to set a task s notepad entry to a specified note The rtems_task_get_note directive allows the user to obtain the note contained in any one of the sixteen notepads of a specified task 5 3 9 Task Deletion RTEMS provides the rtems_task_delete directive to allow a task to delete itself or any other task This directive removes all RTEMS references to the task frees the task s control block removes it from resource wait queues and deallocates its stack as well as the optional floating point context The task s name and ID become inactive at this time and any subsequent references to either of them is invalid In fact RTEMS may reuse the task ID for another task which is created later in the application Unexpired delay timers i e those used by rtems_task_wake_after and rtems task wake when and timeout timers associated with the task are automatically deleted how ever other resources dynamically allocated by the task are NOT automatically returned to RTEMS Therefore before a task is deleted all of its dynamically allocated resourc
163. ecute before the processor is allocated to another ready task of equal priority The length of the timeslice is application dependent and specified in the Configuration Table If timeslicing is disabled RTEMS_NO_TIMESLICE then the task will be allowed to execute until a task of higher priority is made ready If RTEMS_NO_PREEMPT is selected then the timeslicing component is ignored by the scheduler The asynchronous signal processing component is used to determine when received signals are to be processed by the task If signal processing is enabled RTEMS_ASR then signals sent to the task will be processed the next time the task executes If signal processing is disabled RTEMS_NO_ASR then all signals received by the task will remain posted until signal processing is enabled This component affects only tasks which have established a routine to process asynchronous signals The interrupt level component is used to determine which interrupts will be enabled when the task is executing RTEMS_INTERRUPT_LEVEL n specifies that the task will execute at interrupt level n e RTEMS_PREEMPT enable preemption default e RTEMS_NO_PREEMPT disable preemption e RTEMS_NO_TIMESLICE disable timeslicing default e RTEMS_TIMESLICE enable timeslicing e RTEMS_ASR enable ASR processing default e RTEMS_NO_ASR disable ASR processing e RTEMS_INTERRUPT_LEVEL 0 enable all interrupts default 32 RTEMS C User s Guide e RTEMS_INTERRU
164. ed as part of directives which have been invoked by an ISR Applications must adhere to the following rule if proper task scheduling and dispatching is to be performed The interrupt manager must be used for all ISRs which may be interrupted by the highest priority ISR which invokes an RTEMS directive Consider a processor which allows a numerically low interrupt level to interrupt a numer ically greater interrupt level In this example if an RTEMS directive is used in a level 4 ISR then all ISRs which execute at levels 0 through 4 must use the interrupt manager Interrupts are nested whenever an interrupt occurs during the execution of another ISR RTEMS supports efficient interrupt nesting by allowing the nested ISRs to terminate with out performing any dispatch processing Only when the outermost ISR terminates will the postponed dispatching occur 6 2 2 RTEMS Interrupt Levels Many processors support multiple interrupt levels or priorities The exact number of inter rupt levels is processor dependent RTEMS internally supports 256 interrupt levels which are mapped to the processor s interrupt levels For specific information on the mapping be tween RTEMS and the target processor s interrupt levels refer to the Interrupt Processing chapter of the Applications Supplement document for a specific target processor 6 2 3 Disabling of Interrupts by RTEMS During the execution of directive calls critical sections of code may be executed
165. eduled by the processor hardware ASRs are scheduled by RTEMS e ISRs do not execute in the context of a task and may invoke only a subset of directives ASRs execute in the context of a task and may execute any directive e When an ISR is invoked it is passed the vector number as its argument When an ASR is invoked it is passed the signal set as its argument e An ASR has a task mode which can be different from that of the task An ISR does not execute as a task and as a result does not have a task mode 12 2 3 Building a Signal Set A signal set is built by a bitwise OR of the desired signals The set of valid signals is RTEMS SIGNAL O through RTEMS SIGNAL 31 If a signal is not explicitly specified in the signal set then it is not present Signal values are specifically designed to be mutually exclusive therefore bitwise OR and addition operations are equivalent as long as each signal appears exactly once in the component list 122 RTEMS C User s Guide This example demonstrates the signal parameter used when sending the signal set consisting of RTEMS_SIGNAL_6 RTEMS_SIGNAL_15 and RTEMS_SIGNAL_31 The signal parameter pro vided to the rtems_signal_send directive should be RTEMS_SIGNAL_6 RTEMS_SIGNAL_15 RTEMS_SIGNAL_31 12 2 4 Building an ASR Mode In general an ASR s mode is built by a bitwise OR of the desired mode components The set of valid mode components is the same as those allowed with the task_create and tas
166. eier ORI Be gee 70 close a devicez s tossed es eet Teen aee meet 167 communication and synchronization 14 conclude current period 200 196 contdets h i1ookeo eb eie RpRC PH pe PERI PPRE PE 215 Configuration Table 05 222 convert external to internal address 154 convert internal to external address 155 counting semaphores 0 000008 85 CPU Dependent Information Table 229 Create a message queue sv ie See eles tae 103 Create d partition oen ve ors RIP enari ed 129 create a Period reesi Bide teat eave pee in 192 create a pODU c toi tadatn teats so hangs s 151 rete a TEGION ocisscoseiiereri Te EEOSE TERES 139 create a semaphore 2 00 eee eee ee eee 91 create a task si sc sveeusatchotuneseseusatidicees 38 create a timers 2 cases kde d ad C EPERRESDRA Gud 74 create an extension set ssssssss 212 current task mode iii 1 eu e repR ecw 48 current task priority np Re nes 47 D delay a task for an interval 51 delay a task until a wall time 52 delay Siir Kiciendeen dative E Kerne 66 delete a message queue 50000 106 delete a partition 0 eee eee eee 132 delete a period nderit ber pesasi 195 267 delete port re eie RR meyer RE d 153 delete a fOglom sss isin per vehe bee dg 141 delete a semaphore lsseeesesesses 94 dele
167. ems_shutdown_executive the directive is called The rtems_initialize_executive directive provides a conceptually simple way to ini tialize RTEMS However in certain cases this mechanism cannot be used The rtems_initialize_executive_early and rtems_initialize_executive_late directives are provided as an alternative mechanism for initializing RTEMS The rtems_initialize_ executive_early directive returns to the caller BEFORE initiating multitasking The rtems_initialize_executive_late directive is invoked to start multitasking It is criti cal that only one of the RTEMS initialization sequences be used in an application 4 3 2 Shutting Down RTEMS The rtems_shutdown_executive directive is invoked by the application to end multitasking and return control to the board support package The board support package resumes execution at the code immediately following the invocation of the rtems_initialize_ executive directive 4 4 Directives This section details the initialization manager s directives A subsection is dedicated to each of this manager s directives and describes the calling sequence related constants usage and status codes 24 RTEMS C User s Guide 4 4 1 INITIALIZE_EXECUTIVE Initialize RTEMS CALLING SEQUENCE void rtems initialize executive rtems configuration table configuration table rtems cpu table cpu table 3 DIRECTIVE STATUS CODES NONE DESCRIPTION This directive is called when the board support p
168. en gpa eh ieron Pan w IL ese e a xb sap Bote died 34 5 3 1 Creating lasks dead pre RR RR ERR oars dees 34 53 2 Obtaining Task D8 ssc sere tte e Ro RE e 35 5 3 3 Starting and Restarting Tasks cece e eee 35 5 3 4 Suspending and Resuming Tasks 0000 cece eee 35 5 3 5 Delaying the Currently Executing Task 35 5 3 6 Changing Task Priority 0 0 cece eee eee eee 36 5 3 7 Changing Task Mode 0 c cece eee eee ee 36 5 3 8 Notepad Locations cece ence ene ee aes 36 5 3 9 Task Deletion carcere we bee hia E Eaa ee eae 36 Ded Directies uuu iei bb ek qu udi nd E erri lna e tw hates 37 5 4 1 TASK_CREATE Create a task 38 5 4 2 TASK_IDENT Get ID of a task 0000 40 5 4 3 TASK_START Start a task 0 00 eee eee 41 5 4 8 TASK RESTART Restart a task 004 42 5 4 5 TASK DELETE Delete a task sees 43 5 4 6 TASK SUSPEND Suspend a task 2 00 44 5 4 7 TASK RESUME Resume a task 000000 45 5 4 8 TTASK IS SUSPENDED Determine if a task is Suspended Hr e 46 5 4 9 TASK SET PRIORITY Set task priority 47 5 4 10 TASK MODE Change the current task mode 48 5 4 11 TASK_GET_NOTE Get task notepad entry 49 5 4 12 TASK SET NOTE Set task notepad entry 50 5 4 18 TASK WAKE AFTER Wake up after
169. end Add memory to a region e rtems region get segment Get segment from a region e rtems region return segment Return segment to a region e rtems region get segment size Obtain size of a segment e rtems region resize segment Change size of a segment 14 2 Background 14 2 1 Region Manager Definitions A region makes up a physically contiguous memory space with user defined boundaries from which variable sized segments are dynamically allocated and deallocated A segment is a variable size section of memory which is allocated in multiples of a user defined page size This page size is required to be a multiple of four greater than or equal to four For example if a request for a 350 byte segment is made in a region with 256 byte pages then a 512 byte segment is allocated Regions are organized as doubly linked chains of variable sized memory blocks Memory requests are allocated using a first fit algorithm If available the requester receives the number of bytes requested rounded up to the next page size RTEMS requires some over head from the region s memory for each segment that is allocated Therefore an application should only modify the memory of a segment that has been obtained from the region The application should NOT modify the memory outside of any obtained segments and within the region s boundaries while the region is currently active in the system Upon return to the region the free block is coalesced with its nei
170. er 4 Initialization Manager 21 4 Initialization Manager 4 1 Introduction The initialization manager is responsible for initiating and shutting down RTEMS Ini tiating RTEMS involves creating and starting all configured initialization tasks and for invoking the initialization routine for each user supplied device driver In a multiprocessor configuration this manager also initializes the interprocessor communications layer The directives provided by the initialization manager are e rtems_initialize_executive Initialize RTEMS e rtems_initialize_executive_early Initialize RTEMS and do NOT Start Mul titasking e rtems_initialize_executive_late Complete Initialization and Start Multitask ing e rtems_shutdown_executive Shutdown RTEMS 4 2 Background 4 2 1 Initialization Tasks Initialization task s are the mechanism by which RTEMS transfers initial control to the user s application Initialization tasks differ from other application tasks in that they are defined in the User Initialization Tasks Table and automatically created and started by RTEMS as part of its initialization sequence Since the initialization tasks are scheduled using the same algorithm as all other RTEMS tasks they must be configured at a priority and mode which will insure that they will complete execution before other application tasks execute Although there is no upper limit on the number of initialization tasks an application is required to define at
171. er Table for this major number The close entry point is commonly used by device drivers to relinquish exclusive access to a device NOTES This directive may or may not cause the calling task to be preempted This is dependent on the device driver being invoked 168 RTEMS C User s Guide 16 4 8 IO_READ Read from a device CALLING SEQUENCE rtems_status_code rtems_io_read rtems_device_major_number major rtems_device_minor_number minor void argument DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL successfully initialized RTEMS_INVALID_NUMBER invalid major device number DESCRIPTION This directive calls the device driver read routine specified in the Device Driver Table for this major number Read operations typically require a buffer address as part of the argument parameter block The contents of this buffer will be replaced with data from the device NOTES This directive may or may not cause the calling task to be preempted This is dependent on the device driver being invoked Chapter 16 I O Manager 169 16 4 9 IO_WRITE Write to a device CALLING SEQUENCE rtems_status_code rtems_io_write rtems_device_major_number major rtems_device_minor_number minor void argument DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL successfully initialized RTEMS_INVALID_NUMBER invalid major device number DESCRIPTION This directive calls the device driver write routine specified in the Device Driver Table for this maj
172. er created successfully RTEMS INVALID ADDRESS id is NULL RTEMS INVALID NAME invalid timer name RTEMS TOO MANY too many timers created DESCRIPTION This directive creates a timer The assigned timer id is returned in id This id is used to access the timer with other timer manager directives For control and maintenance of the timer RTEMS allocates a TMCB from the local TMCB free pool and initializes it NOTES This directive will not cause the calling task to be preempted Chapter 8 Timer Manager 75 8 4 2 TIMER_IDENT Get ID of a timer CALLING SEQUENCE rtems_status_code rtems timer ident rtems name name rtems id id DIRECTIVE STATUS CODES RTEMS SUCCESSFUL timer identified successfully RTEMS INVALID ADDRESS id is NULL RTEMS INVALID NAME timer name not found DESCRIPTION This directive obtains the timer id associated with the timer name to be acquired If the timer name is not unique then the timer id will match one of the timers with that name However this timer id is not guaranteed to correspond to the desired timer The timer id is used to access this timer in other timer related directives NOTES This directive will not cause the running task to be preempted 76 RTEMS C User s Guide 8 4 3 TIMER CANCEL Cancel a timer CALLING SEQUENCE rtems status code rtems timer cancel rtems id id 23 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL timer canceled successfully RTEM
173. er is e rtems_fatal_error_occurred Invoke the fatal error handler 17 2 Background The fatal error manager is called upon detection of an irrecoverable error condition by either RTEMS or the application software Fatal errors can be detected from three sources e the executive RTEMS e user system code e user application code RTEMS automatically invokes the fatal error manager upon detection of an error it considers to be fatal Similarly the user should invoke the fatal error manager upon detection of a fatal error Each status or dynamic user extension set may include a fatal error handler The fatal error handler in the static extension set can be used to provide access to debuggers and monitors which may be present on the target hardware If any user supplied fatal error handlers are installed the fatal error manager will invoke them If no user handlers are configured or if all the user handler return control to the fatal error manager then the RTEMS default fatal error handler is invoked If the default fatal error handler is invoked then the system state is marked as failed Although the precise behavior of the default fatal error handler is processor specific in general it will disable all maskable interrupts place the error code in a known processor dependent place generally either on the stack or in a register and halt the processor The precise actions of the RTEMS fatal error are discussed in the Default Fatal Erro
174. er is not currently available the task can wait for a printer to become available or return immediately When the task has completed printing it should issue the rtems semaphore release directive to allow other tasks access to the printer Task synchronization may be achieved by creating a semaphore with an initial count of zero One task waits for the arrival of another task by issuing a rtems semaphore obtain directive when it reaches a synchronization point The other task performs a correspond ing rtems semaphore release operation when it reaches its synchronization point thus unblocking the pending task 9 2 1 Nested Resource Access Deadlock occurs when a task owning a binary semaphore attempts to acquire that same semaphore and blocks as result Since the semaphore is allocated to a task it cannot be 86 RTEMS C User s Guide deleted Therefore the task that currently holds the semaphore and is also blocked waiting for that semaphore will never execute again RTEMS addresses this problem by allowing the task holding the binary semaphore to obtain the same binary semaphore multiple times in a nested manner Each rtems_semaphore_ obtain must be accompanied with a rtems_semaphore_release The semaphore will only be made available for acquisition by other tasks when the outermost rtems_semaphore_ obtain is matched with a rtems_semaphore_release Simple binary semaphores do not allow nested access and so can be used for task synchro
175. error handler can be specified in the RTEMS configuration table The User Extension Table field fatal contains the ad dress of the fatal error handler to be executed when the rtems_fatal_error_occurred directive is called If the field is set to NULL or if the configured fatal error handler returns to the executive then the default handler provided by RTEMS is executed This default handler will halt execution on the processor where the error occurred 17 4 Directives This section details the fatal error manager s directives A subsection is dedicated to each of this manager s directives and describes the calling sequence related constants usage and status codes Chapter 17 Fatal Error Manager 173 17 4 1 FATAL_ERROR_OCCURRED Invoke the fatal error handler CALLING SEQUENCE void volatile rtems fatal error occurred uint32 t the error 25 DIRECTIVE STATUS CODES NONE DESCRIPTION This directive processes fatal errors If the FATAL error extension is defined in the configu ration table then the user defined error extension is called If configured and the provided FATAL error extension returns then the RTEMS default error handler is invoked This directive can be invoked by RTEMS or by the user s application code including initialization tasks other tasks and ISRs NOTES This directive supports local operations only Unless the user defined error extension takes special actions such as restarting the calling task th
176. es should be deallocated by the user This may be accomplished by instructing the task to delete itself rather than directly deleting the task Other tasks may instruct a task to delete itself by sending a delete self message event or signal or by restarting the task with special arguments which instruct the task to delete itself Chapter 5 Task Manager 37 5 4 Directives This section details the task manager s directives A subsection is dedicated to each of this manager s directives and describes the calling sequence related constants usage and status codes 38 RTEMS C User s Guide 5 4 1 TASK_CREATE Create a task CALLING SEQUENCE rtems_status_code rtems_task_create rtems_name name rtems_task_priority initial_priority size_t stack_size rtems_mode initial_modes rtems_attribute attribute_set rtems_id id I DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL task created successfully RTEMS_INVALID_ADDRESS id is NULL RTEMS_INVALID_NAME invalid task name RTEMS_INVALID_PRIORITY invalid task priority RTEMS_MP_NOT_CONFIGURED multiprocessing not configured RTEMS_TOO_MANY too many tasks created RTEMS_UNSATISFIED not enough memory for stack FP context RTEMS_TOO_MANY too many global objects DESCRIPTION This directive creates a task which resides on the local node It allocates and initializes a TCB a stack and an optional floating point context area The mode parameter contains values which sets th
177. ess the desired object Simply stated RTEMS allows the entire system both hardware and software to be viewed logically as a single system 23 2 Background RTEMS makes no assumptions regarding the connection media or topology of a multipro cessor system The tasks which compose a particular application can be spread among as many processors as needed to satisfy the application s timing requirements The applica tion tasks can interact using a subset of the RTEMS directives as if they were on the same processor These directives allow application tasks to exchange data communicate and synchronize regardless of which processor they reside upon The RTEMS multiprocessor execution model is multiple instruction streams with multiple data streams MIMD This execution model has each of the processors executing code independent of the other processors Because of this parallelism the application designer can more easily guarantee deterministic behavior By supporting heterogeneous environments RTEMS allows the systems designer to select the most efficient processor for each subsystem of the application Configuring RTEMS for a heterogeneous environment is no more difficult than for a homogeneous one In keeping with RTEMS philosophy of providing transparent physical node boundaries the minimal heterogeneous processing required is isolated in the MPCI layer 23 2 1 Nodes A processor in a RTEMS system is referred to as a node Each node is a
178. essor by either becoming blocked completing their timeslice or being deleted All tasks with the same priority will execute in FIFO order A task enters the ready state due to any of the following conditions e A running task issues a rtems_task_resume directive for a task that is suspended and the task is not blocked waiting on any resource e A running task issues a rtems_message_queue_send rtems_message_queue_ broadcast or a rtems_message_queue_urgent directive which posts a message to the queue on which the blocked task is waiting e A running task issues an rtems_event_send directive which sends an event condi tion to a task which is blocked waiting on that event condition e A running task issues a rtems_semaphore_release directive which releases the semaphore on which the blocked task is waiting e A timeout interval expires for a task which was blocked by a call to the rtems_task_ wake_after directive Chapter 18 Scheduling Concepts 179 A timeout period expires for a task which blocked by a call to the rtems_task_ wake_when directive A running task issues a rtems_region_return_segment directive which releases a segment to the region on which the blocked task is waiting and a resulting segment is large enough to satisfy the task s request A rate monotonic period expires for a task which blocked by a call to the rtems_rate_monotonic_period directive A timeout interval expires for a task which was blocked waiting on a me
179. et signals When the ASR returns to RTEMS the mode and execution path of the interrupted task or ASR is restored to the context prior to entering the ASR 12 4 Directives This section details the signal manager s directives A subsection is dedicated to each of this manager s directives and describes the calling sequence related constants usage and status codes 124 RTEMS C User s Guide 12 4 1 SIGNAL_CATCH Establish an ASR CALLING SEQUENCE rtems_status_code rtems_signal_catch rtems_asr_entry asr_handler rtems_mode mode DIRECTIVE STATUS CODES RTEMS SUCCESSFUL always successful DESCRIPTION This directive establishes an asynchronous signal routine ASR for the calling task The asr handler parameter specifies the entry point of the ASR If asr handler is NULL the ASR for the calling task is invalidated and all pending signals are cleared Any signals sent to a task with an invalid ASR are discarded The mode parameter specifies the execution mode for the ASR This execution mode supersedes the task s execution mode while the ASR is executing NOTES This directive will not cause the calling task to be preempted The following task mode constants are defined by RTEMS e RTEMS_PREEMPT is masked by RTEMS PREEMPT MASK and enables preemption e RTEMS NO PREEMPT is masked by RTEMS_PREEMPT_MASK and disables preemption e RTEMS_NO_TIMESLICE is masked by RTEMS TIMESLICE MASK and disables timeslicing
180. figuration system can automatically generate a POSIX Initialization Threads Table named POSIX Initialization threads with a single entry The following parameters control the generation of that table e CONFIGURE POSIX INIT THREAD TABLE is defined if the user wishes to use a POSIX API Initialization Threads Table The application may choose to use the initializa tion tasks or threads table from another API By default this field is not defined as the user MUST select their own API for initialization tasks e CONFIGURE POSIX HAS OWN INIT THREAD TABLE is defined if the user wishes to de fine their own POSIX API Initialization Threads Table This table should be named POSIX Initialization threads By default this is not defined e CONFIGURE POSIX INIT THREAD ENTRY POINT is the entry point a k a function name of the single initialization thread defined by the POSIX API Initialization Threads Table By default the value is POSIX Init e CONFIGURE POSIX INIT THREAD STACK SIZE is the stack size of the single initial ization thread defined by the POSIX API Initialization Threads Table By default the value is RTEMS MINIMUM STACK SIZE 2 22 2 9 ITRON API Configuration The parameters in this section are used to configure resources for the RTEMS ITRON API They are only relevant if the POSIX API is enabled at configure time using the enable itron option Chapter 22 Configuring a System 221 CONFIGURE_MAXIMUM_ITRON_TASKS
181. formation For example an application could implement task profiling by storing timing statistics in the TCB s extended memory area When a task context switch is being executed the TASK_SWITCH extension could read a real time clock to calculate how long the task be ing swapped out has run as well as timestamp the starting time for the task being swapped in If used the extended memory area for the TCB should be allocated and the TCB extension pointer should be set at the time the task is created or started by either the T ASK CREATE or TASK START extension The application is responsible for managing this extended memory area for the TCBs The memory may be reinitialized by the TASK RESTART extension and should be deallocated by the TASK DELETE extension when the task is Chapter 21 User Extensions Manager 207 deleted Since the TCB extension buffers would most likely be of a fixed size the RTEMS partition manager could be used to manage the application s extended memory area The application could create a partition of fixed size TCB extension buffers and use the partition manager s allocation and deallocation directives to obtain and release the extension buffers 21 2 3 Extensions The sections that follow will contain a description of each extension Each section will contain a prototype of a function with the appropriate calling sequence for the corresponding extension The names given for the C function and its arguments are all
182. fully acquired by returning immediately with a successful return code If the calling task chooses to return immediately and the current semaphore count is zero or negative then a status code is returned indicating that the semaphore is not available If the calling task chooses to wait for a semaphore and the current semaphore count is zero or negative then it is decremented by one and the calling task is placed on the semaphore s wait queue and blocked If the semaphore was created with the RTEMS PRIORITY attribute then the calling task is inserted into the queue according to its priority However if the semaphore was created with the RTEMS FIFO attribute then the calling task is placed at the rear of the wait queue If the binary semaphore was created with the RTEMS_INHERIT_ PRIORITY attribute then the priority of the task currently holding the binary semaphore is guaranteed to be greater than or equal to that of the blocking task If the binary semaphore was created with the RTEMS PRIORITY CEILING attribute a task successfully obtains the semaphore and the priority of that task is greater than the ceiling priority for this semaphore then the priority of the task obtaining the semaphore is elevated to that of the ceiling The timeout parameter specifies the maximum interval the calling task is willing to be blocked waiting for the semaphore If it is set to RTEMS NO TIMEOUT then the calling task will wait forever If the semaphore is av
183. g for a particular status Typical events include arrival of data completion of an action and errors A collection from which resources are allocated A term used to describe the ease with which software can be rehosted on another computer The act of sending an event message semaphore or signal to a task The act of forcing a task to relinquish the processor and dispatching to another task A mechanism used to represent the relative importance of an element in a set of items RTEMS uses priority to determine which task should execute An algorithm that calls for the lower priority task holding a resource to have its priority increased to that of the highest priority task blocked waiting for that resource This avoids the problem of priority inversion A form of indefinite postponement which occurs when a high priority tasks requests access to shared resource currently allocated to low priority task The high priority task must block until the low priority task releases the resource The percentage of processor time used by a task or a set of tasks An RTEMS control structure used to represent on a remote node a task which must block as part of a remote operation Chapter 26 Glossary 259 Proxy Control Block A data structure associated with each proxy used by RTEMS to manage that proxy PTCB An acronym for Partition Control Block PXCB An acronym for Proxy Control Block quantum The application defined unit of time i
184. g with the length of the message When messages are unavailable one of the following situations applies e By default the calling task will wait forever for the message to arrive e Specifying the RTEMS_NO_WAIT option forces an immediate return with an error status code e Specifying a timeout limits the period the task will wait before returning with an error status If the task waits for a message then it is placed in the message queue s task wait queue in either FIFO or task priority order All tasks waiting on a message queue are returned an error code when the message queue is deleted 10 3 4 Sending a Message Messages can be sent to a queue with the rtems_message_queue_send and rtems_message_ queue_urgent directives These directives work identically when tasks are waiting to receive a message A task is removed from the task waiting queue unblocked and the message is copied to a waiting task s message buffer When no tasks are waiting at the queue rtems_message_queue_send places the message at the rear of the message queue while rtems_message_queue_urgent places the message at the front of the queue The message is copied to a message buffer from this message queue s buffer pool and then placed in the message queue Neither directive can successfully send a message to a message queue which has a full queue of pending messages 10 3 5 Broadcasting a Message The rtems_message_queue_broadcast directive sends the same mes
185. ge header file that based on the setting of a variety of macros can automatically produce nearly all of the configuration tables required by an RTEMS application Rather than building the individual tables by hand the application simply specifies the values for the configuration parameters it wishes to set In the following example the configuration information for a simple system with a message queue and a time slice of 50 milliseconds is configured define CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER define CONFIGURE_MICROSECONDS_PER_TICK 1000 1 millisecond define CONFIGURE_TICKS_PER_TIMESLICE 50 50 milliseconds define CONFIGURE_MAXIMUM_TASKS 4 define CONFIGURE_RTEMS_INIT_TASKS_TABLE This system will begin execution with the single initialization task named Init It will be configured to have both a console device driver for standard I O and a clock tick device driver For each configuration parameter in the configuration tables the macro corresponding to that field is discussed Most systems can be easily configured using the confdefs h mech anism The CONFIGURE INIT constant must be defined in order to make confdefs h instantiate the configuration data structures This can only be defined in one source file per application that includes confdefs h or the symbol table will be instantiated multiple times and linking errors produced The user should be aware that the
186. ge of processor time used and can be calculated on a per task or system wide basis Typically the task s worst case execution time will be less than its period For example a periodic task s requirements may state that it should execute for 10 millisec onds every 100 milliseconds Although the execution time may be the average worst or best case the worst case execution time is more appropriate for use when analyzing system behavior under transient overload conditions In contrast an aperiodic task executes at irregular intervals and has only a soft deadline In other words the deadlines for aperiodic tasks are not rigid but adequate response times are desirable For example an aperiodic task may process user input from a terminal Finally a sporadic task is an aperiodic task with a hard deadline and minimum interarrival time The minimum interarrival time is the minimum period of time which exists between successive iterations of the task For example a sporadic task could be used to process the pressing of a fire button on a joystick The mechanical action of the fire button ensures a minimum time period between successive activations but the missile must be launched by a hard deadline 182 RTEMS C User s Guide 19 2 3 Rate Monotonic Scheduling Algorithm The Rate Monotonic Scheduling Algorithm RMS is important to real time systems de signers because it allows one to guarantee that a set of tasks is schedulable A set of task
187. ghbors if free on both sides to produce the largest possible unused block 14 2 2 Building an Attribute Set In general an attribute set is built by a bitwise OR of the desired attribute components The set of valid region attributes is provided in the following table e RTEMS_FIFO tasks wait by FIFO default e RTEMS PRIORITY tasks wait by priority Attribute values are specifically designed to be mutually exclusive therefore bitwise OR and addition operations are equivalent as long as each attribute appears exactly once in the component list An attribute listed as a default is not required to appear in the attribute 136 RTEMS C User s Guide list although it is a good programming practice to specify default attributes If all defaults are desired the attribute RTEMS_DEFAULT_ATTRIBUTES should be specified on this call This example demonstrates the attribute_set parameter needed to create a region with the task priority waiting queue discipline The attribute_set parameter to the rtems_region_ create directive should be RTEMS_PRIORITY 14 2 3 Building an Option Set In general an option is built by a bitwise OR of the desired option components The set of valid options for the rtems_region_get_segment directive are listed in the following table e RTEMS_WAIT task will wait for segment default e RTEMS_NO_WAIT task should not wait Option values are specifically designed to be mutually exclusive therefore bitwise OR and
188. gurations depending on the system hardware configuration Objects such as tasks queues events signals semaphores and memory blocks can be designated as global objects and accessed by any task regardless of which processor the object and the accessing task reside 2 RTEMS C User s Guide The acceptance of a standard for real time executives will produce the same advantages enjoyed from the push for UNIX standardization by AT amp T s System V Interface Definition and IEEE s POSIX efforts A compliant multiprocessing executive will allow close coupling between UNIX systems and real time executives to provide the many benefits of the UNIX development environment to be applied to real time software development Together they provide the necessary laboratory environment to implement real time distributed embed ded systems using a wide variety of computer architectures A study was completed in 1988 within the Research Development and Engineering Center U S Army Missile Command which compared the various aspects of the Ada programming language as they related to the application of Ada code in distributed and or multiple pro cessing systems Several critical conclusions were derived from the study These conclusions have a major impact on the way the Army develops application software for embedded ap plications These impacts apply to both in house software development and contractor developed software A conclusion of the analysis w
189. h directive includes the following sections e Calling sequence e Directive status codes e Description e Notes The following provides an overview of the remainder of this manual Chapter 2 Key Concepts presents an introduction to the ideas which are com mon across multiple RTEMS managers Chapter 3 RTEMS Data Types describes the fundamental data types shared by the services in the RTEMS Classic API Chapter 4 Initialization Manager describes the functionality and directives pro vided by the Initialization Manager Chapter 5 Task Manager describes the functionality and directives provided by the Task Manager Chapter 6 Interrupt Manager describes the functionality and directives pro vided by the Interrupt Manager Chapter 7 Clock Manager describes the functionality and directives provided by the Clock Manager Chapter 8 Timer Manager describes the functionality and directives provided by the Timer Manager Chapter 9 Semaphore Manager describes the functionality and directives pro vided by the Semaphore Manager Chapter 10 Message Manager describes the functionality and directives provided by the Message Manager Chapter 11 Event Manager describes the functionality and directives provided by the Event Manager Chapter 1 Overview Chapter 12 Chapter 13 Chapter 14 Chapter 15 Chapter 16 Chapter 17 Chapter 18 Chapter 19 Chapter 20 Chapter 21 Chapter 22 Chapter
190. h is specified by the user in the Configuration Table 7 2 2 Time and Date Data Structures The clock facilities of the clock manager operate upon calendar time These directives utilize the following date and time structure for the native time and date format struct rtems_tod_control uint32_t year greater than 1987 uint32 t month 1 12 uint32_t day 1 31 uint32_t hour 0 23 uint32 t minute 0 59 x uint32 t second 0 59 x uint32 t ticks elapsed between seconds ys typedef struct rtems tod control rtems time of day The native date and time format is the only format supported when setting the system date and time using the rtems clock get directive Some applications expect to operate on a UNIX style date and time data structure The rtems clock get directive can optionally return the current date and time in the following structure typedef struct uint32_t seconds seconds since RTEMS epoch uint32_t microseconds since last second rtems_clock_time_value The seconds field in this structure is the number of seconds since the RTEMS epoch of January 1 1988 66 RTEMS C User s Guide 7 2 3 Clock Tick and Timeslicing Timeslicing is a task scheduling discipline in which tasks of equal priority are executed for a specific period of time before control of the CPU is passed to another task It is also sometimes referred to as the automatic round robin schedu
191. h place the most significant byte at the smallest address are classified as big endian processors Big endian byte ordering is shown below w ee d o o w ed d o ure w ee d oO N w Sc d o w Chapter 23 Multiprocessing Manager 247 Unfortunately sharing a data structure between big endian and little endian processors requires translation into a common endian format An application designer typically chooses the common endian format to minimize conversion overhead Another issue in the design of shared data structures is the alignment of data structure elements Alignment is both processor and compiler implementation dependent For exam ple some processors allow data elements to begin on any address boundary while others impose restrictions Common restrictions are that data elements must begin on either an even address or on a long word boundary Violation of these restrictions may cause an exception or impose a performance penalty Other issues which commonly impact the design of shared data structures include the rep resentation of floating point numbers bit fields decimal data and character strings In addition the representation method for negative integers could be one s or two s comple ment These factors combine to increase the complexity of designing and manipulating data structures shared between processors RTEMS addressed these issues in the desig
192. har name rtems driver name t device info 35 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL successfully initialized RTEMS_UNSATISFIED name not registered DESCRIPTION This directive returns the major minor number pair associated with the given device name in device info NOTES This directive will not cause the calling task to be preempted 166 RTEMS C User s Guide 16 4 6 IO OPEN Open a device CALLING SEQUENCE rtems status code rtems io open rtems device major number major rtems device minor number minor void argument i DIRECTIVE STATUS CODES RTEMS SUCCESSFUL successfully initialized RTEMS INVALID NUMBER invalid major device number DESCRIPTION This directive calls the device driver open routine specified in the Device Driver Table for this major number The open entry point is commonly used by device drivers to provide exclusive access to a device NOTES This directive may or may not cause the calling task to be preempted This is dependent on the device driver being invoked Chapter 16 I O Manager 167 16 4 7 IO_CLOSE Close a device CALLING SEQUENCE rtems_status_code rtems_io_close rtems_device_major_number major rtems_device_minor_number minor void argument DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL successfully initialized RTEMS_INVALID_NUMBER invalid major device number DESCRIPTION This directive calls the device driver close routine specified in the Device Driv
193. he following C structure 228 RTEMS C User s Guide typedef struct void thread_entry void posix_initialization_threads_table typedef struct int int int int int int int int int int int int maximum_threads maximum_mutexes maximum_condition_variables maximum keys maximum timers maximum queued signals maximum message queues maximum semaphores maximum barriers maximum rwlocks maximum spinlocks number of initialization tasks posix initialization threads table User initialization tasks table posix api configuration table maximum threads maximum mutexes is the maximum number of threads that can be concurrently ac tive created in the system including initialization threads When using the confdefs h mechanism for configuring an RT EMS appli cation the value for this field corresponds to the setting of the macro CONFIGURE MAXIMUM POSIX THREADS If not defined by the applica tion then the CONFIGURE MAXIMUM POSIX THREADS macro defaults to 10 is the maximum number of mutexes that can be concurrently active in the system When using the confdefs h mechanism for config uring an RT EMS application the value for this field corresponds to the setting of the macro CONFIGURE MAXIMUM POSIX MUTEXES If not defined by the application then the CONFIGURE MAXIMUM POSIX MUTEXES macro defaults to 0 maximum condition variables maximum keys is the maximum nu
194. he options parameter allow the calling task to specify whether to wait for a message to become available or return immediately For either option if there is at least one message in the queue then it is copied to buffer size is set to return the length of the message in bytes and this directive returns immediately with a successful return code If the calling task chooses to return immediately and the queue is empty then a status code indicating this condition is returned If the calling task chooses to wait at the message queue and the queue is empty then the calling task is placed on the message wait queue and blocked If the queue was created with the RTEMS PRIORITY option specified then the calling task is inserted into the wait queue according to its priority But if the queue was created with the RTEMS_FIFO option specified then the calling task is placed at the rear of the wait queue A task choosing to wait at the queue can optionally specify a timeout value in the timeout parameter The timeout parameter specifies the maximum interval to wait before the calling task desires to be unblocked If it is set to RTEMS NO TIMEOUT then the calling task will wait forever NOTES The following message receive option constants are defined by RTEMS e RTEMS WAIT task will wait for a message default e RTEMS NO WAIT task should not wait Chapter 10 Message Manager 111 Receiving a message from a global message queue which does n
195. he setting of the macro CONFIGURE_MAXIMUM_SEMAPHORES If not de fined by the application then the CONFIGURE_MAXIMUM_SEMAPHORES macro defaults to 0 maximum_message_queues maximum_partitions maximum regions maximum ports is the maximum number of message queues that can be concurrently active in the system When using the confdefs h mechanism for configuring an RTEMS application the value for this field corre sponds to the setting of the macro CONFIGURE MAXIMUM MESSAGE QUEUES If not defined by the application then the CONFIGURE MAXIMUM MESSAGE QUEUES macro defaults to 0 is the maximum number of partitions that can be concurrently active in the system When using the confdefs h mechanism for config uring an RTEMS application the value for this field corresponds to the setting of the macro CONFIGURE MAXIMUM PARTITIONS If not de fined by the application then the CONFIGURE MAXIMUM PARTITIONS macro defaults to 0 is the maximum number of regions that can be concurrently active in the system When using the confdefs h mechanism for configuring an RTEMS application the value for this field corresponds to the setting of the macro CONFIGURE MAXIMUM REGIONS If not defined by the application then the CONFIGURE MAXIMUM REGIONS macro defaults to 0 is the maximum number of ports into dual port memory areas that can be concurrently active in the system When using the confdefs h mechanism for configuring an RTEMS application
196. hich has been previously recognized by other agencies at tempting to utilize Ada in a distributed or multiprocessing environment is that the Ada programming language does not adequately support multiprocessing Ada does provide a mechanism for multi tasking however this capability exists only for a single processor sys tem The language also does not have inherent capabilities to access global named variables flags or program code These critical features are essential in order for data to be shared between processors However these drawbacks do have workarounds which are sometimes awkward and defeat the intent of software maintainability and portability goals Another conclusion drawn from the analysis was that the run time executives being de livered with the Ada compilers were too slow and inefficient to be used in modern missile systems A run time executive is the core part of the run time system code or operat ing system code that controls task scheduling input output management and memory management Traditionally whenever efficient executive also known as kernel code was required by the application the user developed in house software This software was usually written in assembly language for optimization Because of this shortcoming in the Ada programming language software developers in research and development and contractors for project managed systems are mandated by technology to purchase and utilize off the shelf third pa
197. i ave eter ten y NRA 127 per task variables eee e eee eee eee 39 per task variable 2 cee eee eee 54 56 period imnuUlabion sz e FERE enis 196 periodic task definition 00 181 periodie Tasks ia 5s 26neR Dem eie ehinehecs PES 181 POLES sco iav X PET RU VAG ads FEE eaters aes 149 POSIX API Configuration Table 227 preempllon lRee X9 M RR ERR IER 31 176 priority task 4eablie1b9 eMe RII Meer REA 30 proxy definition i 2il2f2be j rerea dauie 243 put message at front of queue 108 R rate mononitonic tasks 002008 181 Rate Monotonic Scheduling Algorithm definition EET 182 Concept Index read from a device 00 e eee eee 168 receive event condition 4 119 receive message from a queue 110 region attribute set building 135 r gion add MEMOLY 42 sane e ovr Vantaa 142 region definitlon eL6erweeereeteve tir keris 135 TEPON cie ea a dde n PSU E 135 register a device driver 000 161 Iegister devlCe csse Ghd eats cohas ReRGG HAY REY rk 164 release a semaphore cece ee eee ee 97 reset a timer lii aeos te kt ELLE andes 83 resize Segment ecceseipcxrh mer beetes peri Rd 147 restarting a task cies eme nn 42 TesumHg a task 9 peer nie erineda ES 45 return buffer to partitition 134 return segment to region
198. icant impact on the MPCI layer For example the bandwidth of the communications link has an obvious impact on the maximum MPCI throughput The characteristics of a shared network such as Ethernet lend themselves to supporting an MPCI layer These networks provide both the point to point and broadcast capabilities which are expected by RTEMS Chapter 20 Board Support Packages 203 20 5 3 Systems with Mixed Coupling A mixed coupling system is a multiprocessor configuration in which the processors com municate via both shared memory and communications links A unique characteristic of mixed coupling systems is that a node may not have access to all communication methods There may be multiple shared memory areas and communication links Therefore one of the primary functions of the MPCI layer is to efficiently route RTEMS packets between nodes This routing may be based on numerous algorithms In addition the router may provide alternate communications paths in the event of an overload or a partial failure 20 5 4 Heterogeneous Systems Designing an MPCI layer for a heterogeneous system requires special considerations by the developer RTEMS is designed to eliminate many of the problems associated with sharing data in a heterogeneous environment The MPCI layer need only address the representation of thirty two 32 bit unsigned quantities For more information on supporting a heterogeneous system refer the Supporting Hetero geneous Env
199. igning it an extension set ID Newly created extension sets are immediately installed and are invoked upon the next system even supporting an extension 21 3 2 Obtaining Extension Set IDs When an extension set is created RTEMS generates a unique extension set ID and assigns it to the created extension set until it is deleted The extension ID may be obtained by either of two methods First as the result of an invocation of the rtems extension create Chapter 21 User Extensions Manager 211 directive the extension set ID is stored in a user provided location Second the extension set ID may be obtained later using the rtems_extension_ident directive The extension set ID is used by other directives to manipulate this extension set 21 3 3 Deleting an Extension Set The rtems_extension_delete directive is used to delete an extension set The extension set s control block is returned to the ESCB free list when it is deleted An extension set can be deleted by a task other than the task which created the extension set Any subsequent references to the extension s name and ID are invalid 21 4 Directives This section details the user extension manager s directives A subsection is dedicated to each of this manager s directives and describes the calling sequence related constants usage and status codes 212 RTEMS C User s Guide 21 4 1 EXTENSION CREATE Create a extension set CALLING SEQUENCE rtems status code rtems exte
200. implements timeslicing NOTES This directive is typically called from an ISR The microseconds per tick and ticks per timeslice parameters in the Configuration Table contain the number of microseconds per tick and number of ticks per timeslice respectively Chapter 8 Timer Manager 71 8 Timer Manager 8 1 Introduction The timer manager provides support for timer facilities The directives provided by the timer manager are e rtems_timer_create Create a timer e rtems_timer_ident Get ID of a timer e rtems_timer_cancel Cancel a timer e rtems_timer_delete Delete a timer e rtems_timer_fire_after Fire timer after interval e rtems_timer_fire_when Fire timer when specified e rtems_timer_initiate_server Initiate server for task based timers e rtems_timer_server_fire_after Fire task based timer after interval e rtems_timer_server_fire_when Fire task based timer when specified e rtems_timer_reset Reset an interval timer 8 2 Background 8 2 1 Required Support A clock tick is required to support the functionality provided by this manager 8 2 2 Timers A timer is an RTEMS object which allows the application to schedule operations to occur at specific times in the future User supplied timer service routines are invoked by either the rtems_clock_tick directive or a special Timer Server task when the timer fires Timer ser vice routines may perform any operations or directives which normally would be performed b
201. invalid time buffer RTEMS NOT DEFINED system date and time is not set DESCRIPTION This directive blocks a task until the date and time specified in time buffer At the requested date and time the calling task will be unblocked and made ready to execute NOTES The ticks portion of time buffer structure is ignored The timing granularity of this directive is a second A clock tick is required to support the functionality of this directive Chapter 5 Task Manager 53 5 4 15 ITERATE_OVER_ALL_THREADS Iterate Over Tasks CALLING SEQUENCE typedef void rtems_per_thread_routine Thread_Control the_thread Ms void rtems iterate over all threads rtems per thread routine routine 25 DIRECTIVE STATUS CODES NONE DESCRIPTION This directive iterates over all of the existant threads in the system and invokes routine on each of them The user should be careful in accessing the contents of the thread This routine is intended for use in diagnostic utilities and is not intented for routine use in an operational system NOTES There is NO protection while this routine is called Thus it is possible that the thread could be deleted while this is operating By not having protection the user is free to invoke support routines from the C Library which require semaphores for data structures 54 RTEMS C User s Guide 5 4 16 TASK VARIABLE ADD Associate per task variable CALLING SEQUENCE rtems status code rtems
202. ion dynamically changes Therefore the total overhead required by RTEMS dynamically changes 14 3 2 Obtaining Region IDs When a region is created RTEMS generates a unique region ID and assigns it to the created region until it is deleted The region ID may be obtained by either of two methods First as the result of an invocation of the rtems_region_create directive the region ID is stored in a user provided location Second the region ID may be obtained later using the rtems_region_ident directive The region ID is used by other region manager directives to access this region Chapter 14 Region Manager 137 14 3 3 Adding Memory to a Region The rtems_region_extend directive may be used to add memory to an existing region The caller specifies the size in bytes and starting address of the memory being added NOTE Please see the release notes or RTEMS source code for information regarding re strictions on the location of the memory being added in relation to memory already in the region 14 3 4 Acquiring a Segment The rtems_region_get_segment directive attempts to acquire a segment from a specified region If the region has enough available free memory then a segment is returned success fully to the caller When the segment cannot be allocated one of the following situations applies e By default the calling task will wait forever to acquire the segment e Specifying the RTEMS_NO_WAIT option forces an immediate return with an
203. ions regions semaphores ports and rate monotonic periods All RTEMS objects have IDs and user assigned names object oriented A term used to describe systems with common mechanisms for uti lizing a variety of entities Object oriented systems shield the appli cation from implementation details 258 operating system overhead packet partition RTEMS C User s Guide The software which controls all the computer s resources and provides the base upon which application programs can be written The portion of the CPUs processing power consumed by the operat ing system A buffer which contains the messages passed between nodes in a multiprocessor system A packet is the contents of an envelope An RTEMS object which is used to allocate and deallocate fixed size blocks of memory from an dynamically specified area of memory Partition Control Block pending periodic task physical address poll pool portability posting preempt priority priority inheritance priority inversion processor utilization proxy A data structure associated with each partition used by RTEMS to manage that partition A term used to describe a task blocked waiting for an event message semaphore or signal A task which must execute at regular intervals and comply with a hard deadline The actual hardware address of a resource A mechanism used to determine if an event has occurred by periodi cally checkin
204. ironments in the Multiprocessing Manager chapter 204 RTEMS C User s Guide Chapter 21 User Extensions Manager 205 21 User Extensions Manager 21 1 Introduction The RTEMS User Extensions Manager allows the application developer to augment the executive by allowing them to supply extension routines which are invoked at critical system events The directives provided by the user extensions manager are e rtems_extension_create Create an extension set e rtems_extension_ident Get ID of an extension set e rtems_extension_delete Delete an extension set 21 2 Background User extension routines are invoked when the following system events occur e Task creation e Task initiation e Task reinitiation e Task deletion e Task context switch e Post task context switch e Task begin e Task exits e Fatal error detection These extensions are invoked as a function with arguments that are appropriate to the system event 21 2 1 Extension Sets An extension set is defined as a set of routines which are invoked at each of the critical system events at which user extension routines are invoked Together a set of these rou tines typically perform a specific functionality such as performance monitoring or debugger support RTEMS is informed of the entry points which constitute an extension set via the following structure typedef struct rtems_task_create_extension thread_create rtems_task_start_extension thread_start rtems
205. is directive WILL NOT RETURN to the caller The user defined extension for this directive may wish to initiate a global shutdown 174 RTEMS C User s Guide Chapter 18 Scheduling Concepts 175 18 Scheduling Concepts 18 1 Introduction The concept of scheduling in real time systems dictates the ability to provide immediate response to specific external events particularly the necessity of scheduling tasks to run within a specified time limit after the occurrence of an event For example software em bedded in life support systems used to monitor hospital patients must take instant action if a change in the patient s status is detected The component of RTEMS responsible for providing this capability is appropriately called the scheduler The scheduler s sole purpose is to allocate the all important resource of processor time to the various tasks competing for attention The RTEMS scheduler allocates the processor using a priority based preemptive algorithm augmented to provide round robin characteristics within individual priority groups The goal of this algorithm is to guarantee that the task which is executing on the processor at any point in time is the one with the highest priority among all tasks in the ready state There are two common methods of accomplishing the mechanics of this algorithm Both ways involve a list or chain of tasks in the ready state One method is to randomly place tasks in the ready chain forcing the sched
206. ith the specified device name The use of these di rectives frees the application from being dependent on the arbitrary assignment of major numbers in a particular application No device naming conventions are dictated by RT EMS 16 3 2 Accessing an Device Driver The I O manager provides directives which enable the application program to utilize device drivers in a standard manner There is a direct correlation between the RTEMS I O manager directives rtems io initialize rtems io open rtems io close rtems io read rtems io write and rtems io control and the underlying device driver entry points 160 RTEMS C User s Guide 16 4 Directives This section details the I O manager s directives A subsection is dedicated to each of this manager s directives and describes the calling sequence related constants usage and status codes Chapter 16 I O Manager 161 16 4 1 IO REGISTER DRIVER Register a device driver CALLING SEQUENCE rtems status code rtems io register driver rtems device major number major rtems driver address table xdriver table rtems device major number registered major js DIRECTIVE STATUS CODES RTEMS SUCCESSFUL successfully registered RTEMS INVALID NUMBER invalid major device number RTEMS TOO MANY no available major device table slot RTEMS RESOURCE IN USE major device number entry in use DESCRIPTION This directive attempts to add a new device driver to the Device Driver Tabl
207. ith the user defined name The user specifies the association between internal and external representations for the port being created RTEMS allocates a Dual Ported Memory Control Block DPCB from the DPCB free list to maintain the newly created DPMA RTEMS also generates a unique dual ported memory port ID which is returned to the calling task RTEMS does not initialize the dual ported memory area or access any memory within it 15 3 2 Obtaining Port IDs When a port is created RTEMS generates a unique port ID and assigns it to the created port until it is deleted The port ID may be obtained by either of two methods First as the result of an invocation of the rtems_port_create directive the task ID is stored in a user provided location Second the port ID may be obtained later using the rtems_port_ident directive The port ID is used by other dual ported memory manager directives to access this port 150 RTEMS C User s Guide 15 3 3 Converting an Address The rtems_port_external_to_internal directive is used to convert an address from ex ternal to internal representation for the specified port The rtems_port_internal_to_ external directive is used to convert an address from internal to external representation for the specified port If an attempt is made to convert an address which lies outside the specified DPMA then the address to be converted will be returned 15 3 4 Deleting a DPMA Port A port can be removed from the system a
208. ition ORKID These two groups are currently working together with the IEEE P1003 4 commit tee to insure that the functionality of their proposed standards is adopted as the real time extensions to POSIX This emerging standard defines an interface for the development of real time software to ease the writing of real time application programs that are directly portable across multiple real time executive implementations This interface includes both the source code interfaces and run time behavior as seen by a real time application It does not include the details of how a kernel implements these functions The standard s goal is to serve as a complete definition of external interfaces so that application code that conforms to these interfaces will execute properly in all real time executive environments With the use of a standards compliant executive routines that acquire memory blocks create and manage message queues establish and use semaphores and send and receive signals need not be redeveloped for a different real time environment as long as the new environment is compliant with the standard Software developers need only concentrate on the hardware dependencies of the real time system Furthermore most hardware dependencies for real time applications can be localized to the device drivers A compliant executive provides simple and flexible real time multiprocessing It easily lends itself to both tightly coupled and loosely coupled confi
209. ition to be satisfied RTEMS EVENT ANY and RTEMS EVENT ALL are used in the option set parameter are used to specify whether a single event or the complete event set is necessary to satisfy the event condition The event out parameter is returned to the calling task with the value that corresponds to the events in event in that were satisfied If pending events satisfy the event condition then event out is set to the satisfied events and the pending events in the event condition are cleared If the event condition is not satisfied and RTEMS NO WAIT is specified then event_out is set to the currently satisfied events If the calling task chooses to wait then it will block waiting for the event condition If the calling task must wait for the event condition to be satisfied then the timeout parameter is used to specify the maximum interval to wait If it is set to RTEMS NO TIMEOUT then the calling task will wait forever NOTES This directive only affects the events specified in event in Any pending events that do not correspond to any of the events specified in event in will be left pending The following event receive option constants are defined by RTEMS e RTEMS WAIT task will wait for event default e RTEMS NO WAIT task should not wait e RTEMS EVENT ALL return after all events default e RTEMS EVENT ANY return after any events A clock tick is required to support the functionality of this directive 120 RTEMS C User
210. ity and execution mode specified when the task was created The starting address of the task is given in entry point The task s starting argument is contained in argument This argument can be a single value or used as an index into an array of parameter blocks NOTES The calling task will be preempted if its preemption mode is enabled and the task being started has a higher priority Any actions performed on a dormant task such as suspension or change of priority are nullified when the task is initiated via the rtems task start directive 42 RTEMS C User s Guide 5 4 4 TASK_RESTART Restart a task CALLING SEQUENCE rtems_status_code rtems_task_restart rtems_id id rtems_task_argument argument DIRECTIVE STATUS CODES RTEMS SUCCESSFUL task restarted successfully RTEMS INVALID ID task id invalid RTEMS INCORRECT STATE task never started RTEMS_ILLEGAL_ON_REMOTE_OBJECT cannot restart remote task DESCRIPTION This directive resets the task specified by id to begin execution at its original starting address The task s priority and execution mode are set to the original creation values If the task is currently blocked RTEMS automatically makes the task ready A task can be restarted from any state except the dormant state The task s starting argument is contained in argument This argument can be a single value or an index into an array of parameter blocks This new argument may be used to distingui
211. iver_entry close_entry rtems_device_driver_entry read_entry rtems_device_driver_entry write_entry rtems_device_driver_entry control_entry rtems_driver_address_table initialization_entry is the address of the entry point called by rtems_io_initialize to initialize a device driver and its associated devices open_entry is the address of the entry point called by rtems_io_open close_entry is the address of the entry point called by rtems_io_close read_entry is the address of the entry point called by rtems_io_read write_entry is the address of the entry point called by rtems_io_write control_entry is the address of the entry point called by rtems_io_control Driver entry points configured as NULL will always return a status code of RTEMS SUCCESSFUL No user code will be executed in this situation A typical declaration for a Device Driver Table might appear as follows rtems driver address table Driver table 2 1 tty initialize tty open tty close major 0 tty read tty write tty control 232 RTEMS C User s Guide Fs lp_initialize lp_open lp close major 1 NULL lp_write lp_control F More information regarding the construction and operation of device drivers is provided in the I O Manager chapter 22 9 User Extensions Table The User Extensions Table is used to inform RTEMS of the optional user supplied static extension set This table contains one entry for each possible extension Th
212. ization tasks or threads table from another API By default this field is not defined as the user MUST select their own API for initialization tasks CONFIGURE_ITRON_HAS_OWN_INIT_TASK_TABLE is defined if the user wishes to define their own ITRON API Initialization Tasks Table This table should be named ITRON_Initialization_tasks By default this is not defined CONFIGURE_ITRON_INIT_TASK_ENTRY_POINT is the entry point a k a function name of the single initialization task defined by the ITRON API Initialization Tasks Table By default the value is ITRON_Init CONFIGURE_ITRON_INIT_TASK_ATTRIBUTES is the attribute set of the single initial ization task defined by the ITRON API Initialization Tasks Table By default the value is TA_HLNG CONFIGURE_ITRON_INIT_TASK_PRIORITY is the initial priority of the single initial ization task defined by the ITRON API Initialization Tasks Table By default the value is 1 which is the highest priority in the ITRON API CONFIGURE ITRON INIT TASK STACK SIZE is the stack size of the single initializa tion task defined by the ITRON API Initialization Tasks Table By default the value is RTEMS MINIMUM STACK SIZE 22 2 11 Ada Tasks This section defines the system configuration parameters supported by confdefs h related to configuring RTEMS to support a task using Ada tasking with GNAT 222 RTEMS C User s Guide e CONFIGURE_GNAT_RTEMS is defined to inform RTEMS that the GNAT Ada run time is to be used by
213. k issues a rtems_task_suspend directive which blocks either itself or another task in the system e The running task issues a rtems_message_queue_receive directive with the wait option and the message queue is empty e The running task issues an rtems_event_receive directive with the wait option and the currently pending events do not satisfy the request e The running task issues a rtems_semaphore_obtain directive with the wait option and the requested semaphore is unavailable e The running task issues a rtems_task_wake_after directive which blocks the task for the given time interval If the time interval specified is zero the task yields the processor and remains in the ready state e The running task issues a rtems_task_wake_when directive which blocks the task until the requested date and time arrives e The running task issues a rtems_region_get_segment directive with the wait op tion and there is not an available segment large enough to satisfy the task s request e The running task issues a rtems_rate_monotonic_period directive and must wait for the specified rate monotonic period to conclude A blocked task may also be suspended Therefore both the suspension and the blocking condition must be removed before the task becomes ready to run again A task occupies the ready state when it is able to be scheduled to run but currently does not have control of the processor Tasks of the same or higher priority will yield the proc
214. k must complete before the next request for it occurs e The tasks are independent in that a task does not depend on the initiation or completion of requests for other tasks e The execution time for each task without preemption or interruption is constant and does not vary e Any non periodic tasks in the system are special These tasks displace periodic tasks while executing and do not have hard critical deadlines Once the basic schedulability analysis is understood some of the above assumptions can be relaxed and the side effects accounted for 19 2 4 2 Processor Utilization Rule The Processor Utilization Rule requires that processor utilization be calculated based upon the period and execution time of each task The fraction of processor time spent executing task index is Time index Period index The processor utilization can be calculated as follows Utilization 0 for index 1 to maximum_tasks Utilization Utilization Time index Period index To ensure schedulability even under transient overload the processor utilization must adhere to the following rule Utilization maximum tasks 2 1 maximum_tasks 1 As the number of tasks increases the above formula approaches 1n 2 for a worst case uti lization factor of approximately 0 693 Many tasks sets can be scheduled with a greater utilization factor In fact the average processor utilization threshold for a randomly gener ated task set is approximate
215. k s timeslice By default this is 50 e CONFIGURE MEMORY OVERHEAD is set to the number of kilobytes the applications wishes to add to the requirements calculated by confdefs h The default value is 0 e CONFIGURE EXTRA TASK STACKS is set to the number of bytes the applications wishes to add to the task stack requirements calculated by confdefs h This pa rameter is very important If the application creates tasks with stacks larger then the minimum then that memory is NOT accounted for by confdefs h The default value is 0 NOTE The required size of the Executive RAM Work Area is calculated automatically when using the confdefs h mechanism 22 2 3 Device Driver Table This section defines the configuration parameters related to the automatic generation of a Device Driver Table As confdefs h only is aware of a small set of standard device drivers the generated Device Driver Table is suitable for simple applications with no custom device drivers e CONFIGURE HAS OWN DEVICE DRIVER TABLE is defined if the application wishes to provide their own Device Driver Table The table generated is an array of rtems driver address table entries named Device drivers By default this is not defined indicating the confdefs h is providing the device driver table e CONFIGURE MAXIMUM DRIVERS is defined as the number of device drivers per node By default this is set to 10 e CONFIGURE MAXIMUM DEVICES is defined to the number of individual devices tha
216. k_mode directives A complete list of mode options is provided in the following table e RTEMS_PREEMPT is masked by RTEMS_PREEMPT_MASK and enables preemption e RTEMS_NO_PREEMPT is masked by RTEMS_PREEMPT_MASK and disables preemption e RTEMS_NO_TIMESLICE is masked by RTEMS_TIMESLICE_MASK and disables timeslicing e RTEMS_TIMESLICE is masked by RTEMS_TIMESLICE_MASK and enables timeslicing e RTEMS_ASR is masked by RTEMS_ASR_MASK and enables ASR processing e RTEMS_NO_ASR is masked by RTEMS_ASR_MASK and disables ASR processing e RTEMS_INTERRUPT_LEVEL 0 is masked by RTEMS_INTERRUPT_MASK and enables all interrupts e RTEMS_INTERRUPT_LEVEL n is masked by RTEMS_INTERRUPT_MASK and sets inter rupts level n Mode values are specifically designed to be mutually exclusive therefore bitwise OR and addition operations are equivalent as long as each mode appears exactly once in the compo nent list A mode component listed as a default is not required to appear in the mode list although it is a good programming practice to specify default components If all defaults are desired the mode DEFAULT MODES should be specified on this call This example demonstrates the mode parameter used with the rtems signal catch to establish an ASR which executes at interrupt level three and is non preemptible The mode should be set to RTEMS_INTERRUPT_LEVEL 3 RTEMS NO PREEMPT to indicate the desired processor mode and interrupt level 12 3 Operations 12 3
217. ked and an error is returned if any one is out of its valid range NOTES Years before 1988 are invalid The system date and time are based on the configured tick rate number of microseconds in a tick Setting the time forward may cause a higher priority task blocked waiting on a specific time to be made ready In this case the calling task will be preempted after the next clock tick Re initializing RTEMS causes the system date and time to be reset to an uninitialized state Another call to rtems clock set is required to re initialize the system date and time to application specific specifications Chapter 7 Clock Manager 69 7 4 2 CLOCK_GET Get system date and time information CALLING SEQUENCE rtems status code rtems_clock_get rtems clock get options option void time buffer DIRECTIVE STATUS CODES RTEMS SUCCESSFUL current time obtained successfully RTEMS NOT DEFINED system date and time is not set RTEMS INVALID ADDRESS time buffer is NULL DESCRIPTION This directive obtains the system date and time If the caller is attempting to obtain the date and time i e option is set to either RTEMS CLOCK GET SECONDS SINCE EPOCH RTEMS CLOCK GET TOD or RTEMS CLOCK GET TIME VALUE and the date and time has not been set with a previous call to rtems clock set then the RTEMS NOT DEFINED status code is returned The caller can always obtain the number of ticks per second option is RTEMS CLOCK
218. ks execute independently resulting in an asynchronous processing stream Tasks can be dynamically paused for many reasons resulting in a different task being allowed to execute for a period of time The exec utive also provides an interface to other system components such as interrupt handlers and device drivers System components may request the executive to allocate and coordinate resources and to wait for and trigger synchronizing conditions The executive system calls effectively extend the CPU instruction set to support efficient multitasking By causing tasks to travel through well defined state transitions system calls permit an application to demand switch between tasks in response to real time events By proper grouping of responses to stimuli into separate tasks a system can now asyn chronously switch between independent streams of execution directly responding to ex ternal stimuli as they occur This allows the system design to meet critical performance specifications which are typically measured by guaranteed response time and transaction throughput The multiprocessor extensions of RTEMS provide the features necessary to manage the extra requirements introduced by a system distributed across several proces sors It removes the physical barriers of processor boundaries from the world of the system designer enabling more critical aspects of the system to receive the required attention Such a system based on an efficient real time mul
219. l e Fatal Error Management rtems_fatal_error_occurred e Multiprocessing rtems multiprocessing announce 6 4 Directives This section details the interrupt manager s directives A subsection is dedicated to each of this manager s directives and describes the calling sequence related constants usage and status codes 60 RTEMS C User s Guide 6 4 1 INTERRUPT_CATCH Establish an ISR CALLING SEQUENCE rtems_status_code rtems_interrupt_catch rtems_isr_entry new_isr_handler rtems_vector_number vector rtems_isr_entry old_isr_handler js DIRECTIVE STATUS CODES RTEMS SUCCESSFUL ISR established successfully RTEMS INVALID NUMBER illegal vector number RTEMS INVALID ADDRESS illegal ISR entry point or invalid old isr handler DESCRIPTION This directive establishes an interrupt service routine ISR for the specified interrupt vector number The new isr handler parameter specifies the entry point of the ISR The entry point of the previous ISR for the specified vector is returned in old isr handler To release an interrupt vector pass the old handler s address obtained when the vector was first capture NOTES This directive will not cause the calling task to be preempted Chapter 6 Interrupt Manager 61 6 4 2 INTERRUPT_DISABLE Disable Interrupts CALLING SEQUENCE void rtems_interrupt_disable rtems_interrupt_level level 3 this is implemented as a macro and sets level as a side effect
220. l period may be a fraction of a tick less than the interval requested This occurs because the time at which the delay timer is set up occurs at some time between two clock ticks Therefore the first countdown tick occurs in less than the complete time interval for a tick This can be a problem if the clock granularity is large The rate monotonic scheduling algorithm is a hard real time scheduling methodology This methodology provides rules which allows one to guarantee that a set of independent periodic tasks will always meet their deadlines even under transient overload conditions The rate monotonic manager provides directives built upon the Clock Manager s interval timer support routines 16 RTEMS C User s Guide Interval timing is not sufficient for the many applications which require that time be kept in wall time or true calendar form Consequently RTEMS maintains the current date and time This allows selected time operations to be scheduled at an actual calendar date and time For example a task could request to delay until midnight on New Year s Eve before lowering the ball at Times Square The data type rtems_time_of_day is used to specify calendar time in RTEMS services See Section 7 2 2 Time and Date Data Structures page 65 Obviously the directives which use intervals or wall time cannot operate without some ex ternal mechanism which provides a periodic clock tick This clock tick is typically provided by a real time
221. le level used by the task MPCI An acronym for Multiprocessor Communications Interface Layer multiprocessing The simultaneous execution of two or more processes by a multiple processor computer system multiprocessor A computer with multiple CPUs available for executing applications Multiprocessor Communications Interface Layer A set of user provided routines which enable the nodes in a multi processor system to communicate with one another Multiprocessor Configuration Table The data structure defining the characteristics of the multiprocessor target system with which RTEMS will communicate multitasking The alternation of execution amongst a group of processes on a single CPU A scheduling algorithm is used to determine which process executes at which time mutual exclusion A term used to describe the act of preventing other tasks from ac cessing a resource simultaneously nested A term used to describe an ASR that occurs during another ASR or an ISR that occurs during another ISR node A term used to reference a processor running RTEMS in a multipro cessor system non existent The state occupied by an uncreated or deleted task numeric coprocessor A component used in computer systems to enhance performance in mathematically intensive situations It is typically viewed as a logical extension of the primary processor object In this document this term is used to refer collectively to tasks timers message queues partit
222. lid starting count for binary semaphore RTEMS MP NOT CONFIGURED multiprocessing not configured RTEMS TOO MANY too many global objects DESCRIPTION This directive creates a semaphore which resides on the local node The created semaphore has the user defined name specified in name and the initial count specified in count For control and maintenance of the semaphore RTEMS allocates and initializes a SMCB The RTEMS assigned semaphore id is returned in id This semaphore id is used with other semaphore related directives to access the semaphore Specifying PRIORITY in attribute set causes tasks waiting for a semaphore to be serviced according to task priority When FIFO is selected tasks are serviced in First In First Out order NOTES This directive will not cause the calling task to be preempted The priority inheritance and priority ceiling algorithms are only supported for local binary semaphores that use the priority task wait queue blocking discipline The following semaphore attribute constants are defined by RTEMS e RTEMS_FIFO tasks wait by FIFO default e RTEMS PRIORITY tasks wait by priority e RTEMS BINARY SEMAPHORE restrict values to 0 and 1 e RTEMS COUNTING SEMAPHORE no restriction on values default e RTEMS SIMPLE BINARY SEMAPHORE restrict values to 0 and 1 block on nested ac cess allow deletion of locked semaphore e RTEMS NO INHERIT PRIORITY do not use priority inheritance
223. ling algorithm The length of time allocated to each task is known as the quantum or timeslice The system s timeslice is defined as an integral number of ticks and is specified in the Configuration Table The timeslice is defined for the entire system of tasks but timeslicing is enabled and disabled on a per task basis The rtems_clock_tick directive implements timeslicing by decrementing the running task s time remaining counter when both timeslicing and preemption are enabled If the task s timeslice has expired then that task will be preempted if there exists a ready task of equal priority 7 2 4 Delays A sleep timer allows a task to delay for a given interval or up until a given time and then wake and continue execution This type of timer is created automatically by the rtems_task_wake_after and rtems_task_wake_when directives and as a result does not have an RTEMS ID Once activated a sleep timer cannot be explicitly deleted Each task may activate one and only one sleep timer at a time 7 2 5 Timeouts Timeouts are a special type of timer automatically created when the timeout option is used on the rtems_message_queue_receive rtems_event_receive rtems_semaphore_ obtain and rtems_region_get_segment directives Each task may have one and only one timeout active at a time When a timeout expires it unblocks the task with a timeout status code 7 3 Operations 7 3 1 Announcing a Tick RTEMS provides the rtems_clock_tick
224. located from the region will be a multiple of page size bytes in length The assigned region id is returned in id This region id is used as an argument to other region related directives to access the region For control and maintenance of the region RTEMS allocates and initializes an RNCB from the RNCB free pool Thus memory from the region is not used to store the RNCB However some overhead within the region is required by RTEMS each time a segment is constructed in the region Specifying RTEMS PRIORITY in attribute set causes tasks waiting for a segment to be serviced according to task priority Specifying RTEMS_FIFO in attribute set or selecting RTEMS DEFAULT ATTRIBUTES will cause waiting tasks to be serviced in First In First Out order The starting address parameter must be aligned on a four byte boundary The page size parameter must be a multiple of four greater than or equal to eight NOTES This directive will not cause the calling task to be preempted The following region attribute constants are defined by RTEMS e RTEMS_FIFO tasks wait by FIFO default e RTEMS PRIORITY tasks wait by priority 140 RTEMS C User s Guide 14 4 2 REGION_IDENT Get ID of a region CALLING SEQUENCE rtems status code rtems region ident rtems name name rtems id id DIRECTIVE STATUS CODES RTEMS SUCCESSFUL region identified successfully RTEMS INVALID ADDRESS id is NULL RTEMS INVALID NAME region name no
225. ltiprocessing Server which initializes the Multiprocessor Communications Interface Layer verifies multiprocessor system consistency and processes all requests from remote nodes 4 2 3 The Idle Task The Idle Task is the lowest priority task in a system and executes only when no other task is ready to execute This task consists of an infinite loop and will be preempted when any other task is made ready to execute 4 2 4 Initialization Manager Failure The rtems_ifatal_error_occurred directive will be called from rtems_initialize_ executive for any of the following reasons e If either the Configuration Table or the CPU Dependent Information Table is not provided e Ifthe starting address of the RTEMS RAM Workspace supplied by the application in the Configuration Table is NULL or is not aligned on a four byte boundary e If the size of the RTEMS RAM Workspace is not large enough to initialize and configure the system e If the interrupt stack size specified is too small e If multiprocessing is configured and the node entry in the Multiprocessor Configu ration Table is not between one and the maximum_nodes entry e If a multiprocessor system is being configured and no Multiprocessor Communica tions Interface is specified e If no user initialization tasks are configured At least one initialization task must be configured to allow RTEMS to pass control to the application at the end of the executive initialization sequence e If a
226. ltiprocessing table User multiprocessing table rtems api configuration table RTEMS api configuration posix api configuration table POSIX api configuration rtems configuration table work space start is the address of the RTEMS RAM Workspace This area contains items such as the various object control blocks TCBs QCBs and task stacks If the address is not aligned on a four word bound ary then RTEMS will invoke the fatal error handler during rtems_ initialize executive When using the confdefs h mechanism for configuring an RTEMS application the value for this field cor responds to the setting of the macro CONFIGURE EXECUTIVE RAM WORK AREA which defaults to NULL Normally this field should be configured as NULL as BSPs will assign memory for the RTEMS RAM Workspace as part of system initialization Chapter 22 Configuring a System 223 work_space_size microseconds_per_tick ticks per timeslice maximum devices maximum drivers is the calculated size of the RTEMS RAM Workspace The section Sizing the RTEMS RAM Workspace details how to arrive at this number When using the confdefs h mechanism for configuring an RTEMS application the value for this field corresponds to the set ting of the macro CONFIGURE EXECUTIVE RAM SIZE and is calculated based on the other system configuration settings is number of microseconds per clock tick When using the confdefs h mechanism for configuring an RTEMS applicati
227. ly 0 88 19 2 4 3 Processor Utilization Rule Example This example illustrates the application of the Processor Utilization Rule to an application with three critical periodic tasks The following table details the RMS priority period execution time and processor utilization for each task Task RMS Period Execution Processor Priority Time Utilization 1 High 100 15 0 15 2 Medium 200 50 0 25 3 Low 300 100 0 33 184 RTEMS C User s Guide The total processor utilization for this task set is 0 73 which is below the upper bound of 3 2 1 3 1 or 0 779 imposed by the Processor Utilization Rule Therefore this task set is guaranteed to be schedulable using RMS 19 2 4 4 First Deadline Rule If a given set of tasks do exceed the processor utilization upper limit imposed by the Processor Utilization Rule they can still be guaranteed to meet all their deadlines by application of the First Deadline Rule This rule can be stated as follows For a given set of independent periodic tasks if each task meets its first deadline when all tasks are started at the same time then the deadlines will always be met for any combination of start times A key point with this rule is that ALL periodic tasks are assumed to start at the exact same instant in time Although this assumption may seem to be invalid RTEMS makes it quite easy to ensure By having a non preemptible user initialization task all application t
228. mber of condition variables that can be concur rently active in the system When using the confdefs h mechanism for configuring an RTEMS application the value for this field cor responds to the setting of the macro CONFIGURE MAXIMUM POSIX CONDITION VARIABLES If not defined by the application then the CONFIGURE MAXIMUM POSIX CONDITION VARIABLES macro defaults to 0 is the maximum number of keys that can be concurrently active in the system When using the confdefs h mechanism for configuring an RTEMS application the value for this field corresponds to the setting of the macro CONFIGURE MAXIMUM POSIX KEYS If not defined by Chapter 22 Configuring a System 229 maximum timers the application then the CONFIGURE MAXIMUM POSIX KEYS macro defaults to 0 is the maximum number of POSIX timers that can be concurrently active in the system When using the confdefs h mechanism for configuring an RTEMS application the value for this field cor responds to the setting of the macro CONFIGURE MAXIMUM POSIX TIMERS If not defined by the application then the CONFIGURE MAXIMUM POSIX TIMERS macro defaults to 0 maximum queued signals is the maximum number of queued signals that can be concur rently pending in the system When using the confdefs h mech anism for configuring an RTEMS application the value for this field corresponds to the setting of the macro CONFIGURE MAXIMUM POSIX QUEUED SIGNALS If not defined by the application the
229. mer fire after and rtems timer server fire after directives initiate a timer to fire a user provided timer service routine after the specified number of clock ticks have elapsed When the interval has elapsed the timer service routine will be invoked from the rtems clock tick directive if it was initiated by the rtems timer fire after directive and from the Timer Server task if initiated by the rtems timer server fire after directive 8 3 4 Initiating a Time of Day Timer The rtems timer fire when and rtems timer server fire when directive initiate a timer to fire a user provided timer service routine when the specified time of day has been reached When the interval has elapsed the timer service routine will be invoked from the Chapter 8 Timer Manager 73 rtems_clock_tick directive by the rtems_timer_fire_when directive and from the Timer Server task if initiated by the rtems_timer_server_fire_when directive 8 3 5 Canceling a Timer The rtems_timer_cancel directive is used to halt the specified timer Once canceled the timer service routine will not fire unless the timer is reinitiated The timer can be reinitiated using the rtems_timer_reset rtems_timer_fire_after and rtems_timer_fire_when directives 8 3 6 Resetting a Timer The rtems_timer_reset directive is used to restore an interval timer initiated by a pre vious invocation of rtems_timer_fire_after or rtems_timer_server_fire_after to its original interval length If the time
230. mes An object name is an unsigned thirty two bit entity associated with the object by the user The data type rtems name is used to store object names Although not required by RTEMS object names are often composed of four ASCII char acters which help identify that object For example a task which causes a light to blink might be called LITE The rtems build name routine is provided to build an object name from four ASCII characters The following example illustrates this rtems object name my name my name rtems build name L I T E However it is not required that the application use ASCII characters to build object names For example if an application requires one hundred tasks it would be difficult to assign meaningful ASCII names to each task A more convenient approach would be to name them the binary values one through one hundred respectively 14 RTEMS C User s Guide 2 2 2 Object IDs An object ID is a unique unsigned thirty two bit entity composed of three parts object class node and index The data type rtems_id is used to store object IDs 31 26 25 16 15 0 Class Node Index The most significant six bits are the object class The next ten bits are the number of the node on which this object was created The node number is always one 1 in a single processor system The least significant sixteen bits form an identifier within a particular object type This identifier c
231. mpci get packet entry is the address of the entry point to the get packet routine for an MPCI implementation rtems mpci initialization entry is the address of the entry point to the initial ization routine for an MPCI implementation rtems mpci receive packet entry is the address of the entry point to the receive packet routine for an MPCI implementation rtems mpci return packet entry is the address of the entry point to the return packet routine for an MPCI implementation rtems mpci send packet entry is the address of the entry point to the send packet routine for an MPCI implementation rtems mpci table is the data structure containing the configuration information for an MPCI rtems name is the data type used to contain the name of a Classic API object It is an unsigned thirty two bit integer which can be treated as a numeric value or initialized using rtems build name to contain four ASCII characters rtems option is the data type used to specify which behavioral options the caller desires It is commonly used with potentially blocking directives to specify whether the caller is willing to block or return immediately with an error indicating that the resource was not available rtems packet prefix is the data structure that defines the first bytes in every packet sent between nodes in an RTEMS multiprocessor system It contains routing information that is expected to be used by the MPCI layer rtems signal set is the
232. mpci_entry user_mpci_initialization rtems_configuration_table configuration where configuration is the address of the user s Configuration Table Operations on global objects cannot be performed until this component is invoked The INITIALIZATION com ponent is invoked only once in the life of any system If the MPCI layer cannot be success fully initialized the fatal error manager should be invoked by this routine One of the primary functions of the MPCI layer is to provide the executive with packet buffers The INITIALIZATION routine must create and initialize a pool of packet buffers There must be enough packet buffers so RTEMS can obtain one whenever needed 23 3 2 GET_PACKET The GET PACKET component of the user provided MPCI layer is called when RTEMS must obtain a packet buffer to send or broadcast a message This component should be adhere to the following prototype rtems_mpci_entry user_mpci_get_packet rtems_packet_prefix packet where packet is the address of a pointer to a packet This routine always succeeds and upon return packet will contain the address of a packet If for any reason a packet cannot be successfully obtained then the fatal error manager should be invoked RT EMS has been optimized to avoid the need for obtaining a packet each time a message is sent or broadcast For example RTEMS sends response messages RR back to the originator in the same packet in which the request message RQ arri
233. ms id id 25 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL timer reset successfully RTEMS INVALID ID invalid timer id RTEMS NOT DEFINED attempted to reset a when or newly created timer DESCRIPTION This directive resets the timer associated with id This timer must have been previously ini tiated with either the rtems timer fire after or rtems timer server fire after di rective If active the timer is canceled after which the timer is reinitiated using the same in terval and timer service routine which the original rtems timer fire after rtems timer server fire after directive used NOTES If the timer has not been used or the last usage of this timer was by a rtems timer fire when or rtems timer server fire when directive then the RTEMS NOT DEFINED error is returned Restarting a cancelled after timer results in the timer being reinitiated with its previous timer service routine and interval This directive will not cause the running task to be preempted 84 RTEMS C User s Guide Chapter 9 Semaphore Manager 85 9 Semaphore Manager 9 1 Introduction The semaphore manager utilizes standard Dijkstra counting semaphores to provide syn chronization and mutual exclusion capabilities The directives provided by the semaphore manager are e rtems_semaphore_create Create a semaphore e rtems semaphore ident Get ID of a semaphore e rtems semaphore delete Delete a semaphore e rtems semaphore obtain
234. n e priority inheritance e responsive interrupt management e dynamic memory allocation e high level of user configurability This manual describes the usage of RT EMS for applications written in the C programming language Those implementation details that are processor dependent are provided in the Applications Supplement documents A supplement document which addresses specific architectural issues that affect RTEMS is provided for each processor type that is supported 1 2 Real time Application Systems Real time application systems are a special class of computer applications They have a complex set of characteristics that distinguish them from other software problems Gen erally they must adhere to more rigorous requirements The correctness of the system depends not only on the results of computations but also on the time at which the results are produced The most important and complex characteristic of real time application sys tems is that they must receive and respond to a set of external stimuli within rigid and critical time constraints referred to as deadlines Systems can be buried by an avalanche of interdependent asynchronous or cyclical event streams Deadlines can be further characterized as either hard or soft based upon the value of the results when produced after the deadline has passed A deadline is hard if the results have no value or if their use will result in a catastrophic event In contrast results which are
235. n be concurrently active The default for this field is 0 Chapter 22 Configuring a System 219 CONFIGURE_MAXIMUM_PARTITIONS is the maximum number of Classic API partitions that can be concurrently active The default for this field is 0 CONFIGURE_MAXIMUM_REGIONS is the maximum number of Classic API regions that can be concurrently active The default for this field is 0 CONFIGURE_MAXIMUM_PORTS is the maximum number of Classic API ports that can be concurrently active The default for this field is 0 CONFIGURE_MAXIMUM_PERIODS is the maximum number of Classic API rate mono tonic periods that can be concurrently active The default for this field is 0 CONFIGURE MAXIMUM USER EXTENSIONS is the maximum number of Classic API user extensions that can be concurrently active The default for this field is 0 22 2 6 Classic API Initialization Tasks Table Configuration The confdefs h configuration system can automatically generate an Initialization Tasks Table named Initialization_tasks with a single entry The following parameters control the generation of that table CONFIGURE_RTEMS_INIT_TASKS_TABLE is defined if the user wishes to use a Classic RTEMS API Initialization Task Table The application may choose to use the initialization tasks or threads table from another API By default this field is not defined as the user MUST select their own API for initialization tasks CONFIGURE_HAS_OWN_INIT_TASK_TABLE is defined if
236. n initialization code Because inter rupts are enabled automatically by RTEMS as part of the rtems_initialize_executive directive the Interrupt Vector Table MUST be set before this directive is invoked to insure correct interrupt vectoring The processor s Interrupt Vector Table must be accessible by RTEMS as it will be modified by the rtems_interrupt_catch directive On some CPUs RTEMS installs it s own Interrupt Vector Table as part of initialization and thus these requirements are met automatically The reset code which is executed before the call to rtems_initialize_executive has the following requirements e Must not make any RTEMS directive calls e If the processor supports multiple privilege levels must leave the processor in the most privileged or supervisory state e Must allocate a stack of at least RTEMS_MINIMUM_STACK_SIZE bytes and initialize the stack pointer for the rtems_initialize_executive directive 200 RTEMS C User s Guide e Must initialize the processor s Interrupt Vector Table e Must disable all maskable interrupts e If the processor supports a separate interrupt stack must allocate the interrupt stack and initialize the interrupt stack pointer The rtems_initialize_executive directive does not return to the initialization code but causes the highest priority initialization task to begin execution Initialization tasks are used to perform both local and global application initialization which is dependent
237. n of the packets used to communicate between nodes The RTEMS packet format is designed to allow the MPCI layer to perform all necessary conversion without burdening the developer with the details of the RT EMS packet format As a result the MPCI layer must be aware of the following e All packets must begin on a four byte boundary e Packets are composed of both RT EMS and application data All RTEMS data is treated as thirty two 32 bit unsigned quantities and is in the first RTEMS MINIMUM UNSIGNED32S TO CONVERT thirty two 32 quantities of the packet e The RTEMS data component of the packet must be in native endian format Endian conversion may be performed by either the sending or receiving MPCI layer e RTEMS makes no assumptions regarding the application data component of the packet 23 4 Operations 23 4 1 Announcing a Packet The rtems multiprocessing announce directive is called by the MPCI layer to inform RTEMS that a packet has arrived from another node This directive can be called from an interrupt service routine or from within a polling routine 23 5 Directives This section details the additional directives required to support RTEMS in a multiprocessor configuration A subsection is dedicated to each of this manager s directives and describes the calling sequence related constants usage and status codes 248 RTEMS C User s Guide 23 5 1 MULTIPROCESSING_ANNOUNCE Announce the arrival of a packet CALLING SEQUE
238. n task If this macro is not defined by the application then this defaults to RTEMS_DEFAULT_ ATTRIBUTES e CONFIGURE_INIT_TASK_ENTRY_POINT is the entry point of the single initialization task If this macro is not defined by the application then this defaults to the C language routine Init e CONFIGURE_INIT_TASK_INITIAL_MODES is the initial execu tion modes of the single initialization task If this macro is not defined by the application then this defaults to RTEMS_ NO_PREEMPT e CONFIGURE_INIT_TASK_ARGUMENTS is the argument passed to the of the single initialization task If this macro is not defined by the application then this defaults to 0 has the option to have value for this field corresponds to the setting of the macro User initialization tasks table is the address of the Initialization Task Table This table contains the information needed to create and start each of the initializa tion tasks The format of this table will be discussed below When using the confdefs h mechanism for configuring an RTEMS appli cation the value for this field corresponds to the setting of the macro CONFIGURE EXECUTIVE RAM WORK AREA 22 5 POSIX API Configuration Table The POSIX API Configuration Table is used to configure the managers which constitute the POSIX API for a particular application For example the user can configure the maximum number of threads for this application The POSIX API Configuration Table is defined in t
239. n the CONFIGURE MAXIMUM POSIX QUEUED SIGNALS macro defaults to 0 number of initialization threads is the number of initialization threads configured At least one ini tialization threads must be configured When using the confdefs h mechanism for configuring an RTEMS application the user must define the CONFIGURE POSIX INIT THREAD TABLE to indicate that there is one or more POSIX initialization thread If the application only has one POSIX initialization thread then the automatically generated POSIX Initialization Thread Table will be sufficient The following macros correspond to the single initialization task e CONFIGURE POSIX INIT THREAD ENTRY POINT is the entry point of the thread If this macro is not defined by the ap plication then this defaults to the C routine POSIX Init e CONFIGURE POSIX INIT TASK STACK SIZE is the stack size of the single initialization thread If this macro is not defined by the application then this defaults to RTEMS MINIMUM STACK SIZE 2 User initialization threads table is the address of the Initialization Threads Table This table con tains the information needed to create and start each of the initial ization threads The format of each entry in this table is defined in the posix initialization threads table structure When using the confdefs h mechanism for configuring an RTEMS application the value for this field corresponds to the address of the POSIX Initialization thre
240. n which the processor is allo cated queue Alternate term for message queue QCB An acronym for Message Queue Control Block ready A task occupies this state when it is available to be given control of the CPU real time A term used to describe systems which are characterized by requiring deterministic response times to external stimuli The external stimuli require that the response occur at a precise time or the response is incorrect reentrant A term used to describe routines which do not modify themselves or global variables region An RTEMS object which is used to allocate and deallocate variable size blocks of memory from a dynamically specified area of memory Region Control Block A data structure associated with each region used by RTEMS to manage that region registers Registers are locations physically located within a component typi cally used for device control or general purpose storage remote Any object that does not reside on the local node remote operation The manipulation of an object which does not reside on the same node as the calling task return code Also known as error code or return value resource A hardware or software entity to which access must be controlled resume Removing a task from the suspend state If the task s state is ready following a call to the rtems_task_resume directive then the task is available for scheduling return code A value returned by RTEMS directives to indicate the
241. nce the executive was initialized and the number of ticks per second The information returned by the rtems_clock_get directive is dependent on the option selected by the caller This is specified using one of the following constants associated with the enumerated type rtems_clock_get_options e RTEMS_CLOCK_GET_TOD obtain native style date and time e RTEMS_CLOCK_GET_TIME_VALUE obtain UNIX style date and time e RTEMS_CLOCK_GET_TICKS_SINCE_BOOT obtain number of ticks since RTEMS was initialized e RTEMS_CLOCK_GET_SECONDS_SINCE_EPOCH obtain number of seconds since RTEMS epoch e RTEMS_CLOCK_GET_TICKS_PER_SECOND obtain number of clock ticks per second Calendar time operations will return an error code if invoked before the date and time have been set 7 4 Directives This section details the clock manager s directives A subsection is dedicated to each of this manager s directives and describes the calling sequence related constants usage and status codes 68 RTEMS C User s Guide 7 4 1 CLOCK_SET Set system date and time CALLING SEQUENCE rtems_status_code rtems_clock_set rtems_time_of_day time_buffer 25 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL date and time set successfully RTEMS INVALID ADDRESS time buffer is NULL RTEMS INVALID CLOCK invalid time of day DESCRIPTION This directive sets the system date and time The date time and ticks in the time buffer structure are all range chec
242. nd returned to RTEMS with the rtems_port_ delete directive When a port is deleted its control block is returned to the DPCB free list 15 4 Directives This section details the dual ported memory manager s directives A subsection is dedicated to each of this manager s directives and describes the calling sequence related constants usage and status codes Chapter 15 Dual Ported Memory Manager 151 15 4 1 PORT_CREATE Create a port CALLING SEQUENCE rtems_status_code rtems_port_create rtems_name name void internal start void external start uint32 t length rtems id id 25 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL port created successfully RTEMS INVALID NAME invalid port name RTEMS INVALID ADDRESS address not on four byte boundary RTEMS INVALID ADDRESS id is NULL RTEMS TOO MANY too many DP memory areas created DESCRIPTION This directive creates a port which resides on the local node for the specified DPMA The assigned port id is returned in id This port id is used as an argument to other dual ported memory manager directives to convert addresses within this DPMA For control and maintenance of the port RTEMS allocates and initializes an DPCB from the DPCB free pool Thus memory from the dual ported memory area is not used to store the DPCB NOTES The internal address and external address parameters must be on a four byte boundary This directive will not cause the calling task
243. new task has been swapped in A value of NULL indicates that no exten sion is provided As this routine is invoked after saving the current task s context and before restoring the heir task s context it is not necessary for this routine to save and restore any registers is the address of the user supplied subroutine which is invoked im mediately before a task begins execution It is invoked in the context of the beginning task A value of NULL indicates that no extension is provided is the address of the user supplied subroutine which is invoked when a task exits This procedure is responsible for some action which will allow the system to continue execution i e delete or restart the task or to terminate with a fatal error If this field is set to NULL the default RTEMS TASK_EXITTED handler will be invoked 234 RTEMS C User s Guide fatal is the address of the user supplied subroutine for the FATAL exten sion This RTEMS extension of fatal error handling is called from the rtems_fatal_error_occurred directive If the user s fatal er ror handler returns or if this entry is NULL then the default RTEMS fatal error handler will be executed A typical declaration for a User Extension Table which defines the TASK CREATE TASK_DELETE TASK_SWITCH and FATAL extension might appear as follows rtems_extensions_table User_extensions task_create_extension NULL NULL task_delete_extension task_switch_extension NULL
244. ngth and buffer size and returned to the calling task along with a unique partition ID 13 3 2 Obtaining Partition IDs When a partition is created RTEMS generates a unique partition ID and assigned it to the created partition until it is deleted The partition ID may be obtained by either of two methods First as the result of an invocation of the rtems_partition_create directive the partition ID is stored in a user provided location Second the partition ID may be obtained later using the rtems_partition_ident directive The partition ID is used by other partition manager directives to access this partition 13 3 3 Acquiring a Buffer A buffer can be obtained by calling the rtems_partition_get_buffer directive If a buffer is available then it is returned immediately with a successful return code Otherwise an unsuccessful return code is returned immediately to the caller Tasks cannot block to wait for a buffer to become available 13 3 4 Releasing a Buffer Buffers are returned to a partition s free buffer chain with the rtems_partition_return_ buffer directive This directive returns an error status code if the returned buffer was not previously allocated from this partition 13 3 5 Deleting a Partition The rtems_partition_delete directive allows a partition to be removed and returned to RTEMS When a partition is deleted the PTCB for that partition is returned to the PTCB free list A partition with buffers still allocated can
245. nitiate the period_1 period for 100 ticks and return immediately Subsequent invocations of the rtems rate monotonic period directive for period 1 will result in the task blocking for the remainder of the 100 tick period The period 2 period is used to control the execution time of the two sets of actions within each 100 tick period established by period_1 The rtems rate monotonic cancel period 2 call is performed to ensure that the period 2 period does not expire while the task is blocked on the period 1 period If this cancel operation were not performed every time the rtems rate monotonic period period 2 40 call is ex ecuted except for the initial one a directive status of RTEMS TIMEOUT is returned It is important to note that every time this call is made the period 2 period will be initiated immediately and the task will not block If for any reason the task misses any deadline the rtems rate monotonic period direc tive will return the RTEMS TIMEOUT directive status If the above task misses its deadline it will delete the rate monotonic periods and itself 19 4 Directives This section details the rate monotonic manager s directives A subsection is dedicated to each of this manager s directives and describes the calling sequence related constants usage and status codes 192 RTEMS C User s Guide 19 4 1 RATE MONOTONIC CREATE Create a rate monotonic period CALLING SEQUENCE rtems_status_code rtem
246. not be deleted Any task attempting to do so will be returned an error status code 13 4 Directives This section details the partition manager s directives A subsection is dedicated to each of this manager s directives and describes the calling sequence related constants usage and status codes Chapter 13 Partition Manager 129 13 4 1 PARTITION_CREATE Create a partition CALLING SEQUENCE rtems status code rtems partition create rtems name name void starting address uint32 t length uint32 t buffer size rtems attribute attribute set rtems id id 5 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL partition created successfully RTEMS INVALID NAME invalid partition name RTEMS TOO MANY too many partitions created RTEMS INVALID ADDRESS address not on four byte boundary RTEMS INVALID ADDRESS starting address is NULL RTEMS INVALID ADDRESS id is NULL RTEMS INVALID SIZE length or buffer size is 0 RTEMS INVALID SIZE length is less than the buffer size RTEMS INVALID SIZE buffer size not a multiple of 4 RTEMS MP NOT CONFIGURED multiprocessing not configured RTEMS TOO MANY too many global objects DESCRIPTION This directive creates a partition of fixed size buffers from a physically contiguous memory space which starts at starting address and is length bytes in size Each allocated buffer is to be of buffer size in bytes The assigned partition id is returned in id This
247. nsion create C rtems name name rtems extensions table table rtems id id js DIRECTIVE STATUS CODES RTEMS SUCCESSFUL extension set created successfully RTEMS INVALID NAME invalid extension set name RTEMS TOO MANY too many extension sets created DESCRIPTION This directive creates a extension set The assigned extension set id is returned in id This id is used to access the extension set with other user extension manager directives For control and maintenance of the extension set RTEMS allocates an ESCB from the local ESCB free pool and initializes it NOTES This directive will not cause the calling task to be preempted Chapter 21 User Extensions Manager 213 21 4 2 EXTENSION IDENT Get ID of a extension set CALLING SEQUENCE rtems status code rtems extension ident rtems name name rtems id id DIRECTIVE STATUS CODES RTEMS SUCCESSFUL extension set identified successfully RTEMS INVALID NAME extension set name not found DESCRIPTION This directive obtains the extension set id associated with the extension set name to be acquired If the extension set name is not unique then the extension set id will match one of the extension sets with that name However this extension set id is not guaranteed to correspond to the desired extension set The extension set id is used to access this extension set in other extension set related directives NOTES This directive will not cause the
248. nstants RTEMS NOTEPAD O through RTEMS NOTEPAD 15 Setting a notepad location of a global task which does not reside on the local node will generate a request to the remote node to set the specified notepad entry Chapter 5 Task Manager 51 5 4 13 TASK WAKE AFTER Wake up after interval CALLING SEQUENCE rtems_status_code rtems task wake after rtems interval ticks 23 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL always successful DESCRIPTION This directive blocks the calling task for the specified number of system clock ticks When the requested interval has elapsed the task is made ready The rtems clock tick directive automatically updates the delay period NOTES Setting the system date and time with the rtems clock set directive has no effect on a rtems task wake after blocked task A task may give up the processor and remain in the ready state by specifying a value of RTEMS YIELD PROCESSOR in ticks The maximum timer interval that can be specified is the maximum value which can be represented by the uint32 t type A clock tick is required to support the functionality of this directive 52 RTEMS C User s Guide 5 4 14 TASK WAKE WHEN Wake up when specified CALLING SEQUENCE rtems status code rtems task wake when rtems time of day time buffer 23 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL awakened at date time successfully RTEMS INVALID ADDRESS time buffer is NULL RTEMS INVALID TIME OF DAY
249. nts sent are left pending NOTES Specifying RTEMS SELF for id results in the event set being sent to the calling task Identical events sent to a task are not queued In other words the second and subsequent posting of an event to a task before it can perform an rtems event receive has no effect The calling task will be preempted if it has preemption enabled and a higher priority task is unblocked as the result of this directive Sending an event set to a global task which does not reside on the local node will generate a request telling the remote node to send the event set to the appropriate task Chapter 11 Event Manager 119 11 4 2 EVENT_RECEIVE Receive event condition CALLING SEQUENCE rtems_status_code rtems_event_receive rtems event set event in rtems option option set rtems interval ticks rtems event set event out DIRECTIVE STATUS CODES RTEMS SUCCESSFUL event received successfully RTEMS_UNSATISFIED input event not satisfied RTEMS NO WAIT RTEMS INVALID ADDRESS event out is NULL RTEMS TIMEOUT timed out waiting for event DESCRIPTION This directive attempts to receive the event condition specified in event_in If event in is set to RTEMS PENDING EVENTS then the current pending events are returned in event out and left pending The RTEMS WAIT and RTEMS NO WAIT options in the option set parameter are used to specify whether or not the task is willing to wait for the event cond
250. number RTEMS assumes that node numbers start at one and increase sequentially This assumption can be used Chapter 22 Configuring a System 235 maximum nodes to advantage by the user supplied MPCI layer Typically this re quirement is made when the node numbers are used to calculate the address of inter processor communication links Zero should be avoided as a node number because some MPCI layers use node zero to represent broadcasted packets Thus it is recommended that node numbers start at one and increase sequentially When us ing the confdefs h mechanism for configuring an RTEMS applica tion the value for this field corresponds to the setting of the macro CONFIGURE MP NODE NUMBER If not defined by the application then the CONFIGURE MP NODE NUMBER macro defaults to the value of the NODE NUMBER macro which is set on the compiler command line by the RTEMS Multiprocessing Test Suites is the number of processor nodes in the system When using the confdefs h mechanism for configuring an RTEMS application the value for this field corresponds to the setting of the macro CONFIGURE_MP_MAXIMUM_NODES If not defined by the application then the CONFIGURE_MP_MAXIMUM_NODES macro defaults to the value 2 maximum global objects maximum proxies User mpci table is the maximum number of global objects which can exist at any given moment in the entire system If this parameter is not the same on all nodes in the system then a f
251. ny of the user initialization tasks cannot be created or started successfully 4 3 Operations 4 3 1 Initializing RTEMS The rtems initialize executive directive is called by the board support package at the completion of its initialization sequence RTEMS assumes that the board support pack age successfully completed its initialization activities The rtems initialize executive directive completes the initialization sequence by performing the following actions e Initializing internal RTEMS variables e Allocating system resources e Creating and starting the System Initialization Task e Creating and starting the Idle Task e Creating and starting the user initialization task s and e Initiating multitasking Chapter 4 Initialization Manager 23 This directive MUST be called before any other RTEMS directives The effect of calling any RTEMS directives before rtems_initialize_executive is unpredictable Many of RTEMS actions during initialization are based upon the contents of the Configuration Table and CPU Dependent Information Table For more information regarding the format and contents of these tables please refer to the chapter Configuring a System The final step in the initialization sequence is the initiation of multitasking When the scheduler and dispatcher are enabled the highest priority ready task will be dispatched to run Control will not be returned to the board support package after multitasking is enabled until rt
252. o RTEMS with the rtems_region_ delete directive When a region is deleted its control block is returned to the RNCB free list A region with segments still allocated is not allowed to be deleted Any task attempting to do so will be returned an error As a result of this directive all tasks blocked waiting to 138 RTEMS C User s Guide obtain a segment from the region will be readied and returned a status code which indicates that the region was deleted 14 4 Directives This section details the region manager s directives A subsection is dedicated to each of this manager s directives and describes the calling sequence related constants usage and status codes Chapter 14 Region Manager 139 14 4 1 REGION_CREATE Create a region CALLING SEQUENCE rtems_status_code rtems_region_create rtems_name name void starting address uint32 t length uint32 t page size rtems attribute attribute set rtems id id 5 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL region created successfully RTEMS INVALID NAME invalid region name RTEMS INVALID ADDRESS id is NULL RTEMS INVALID ADDRESS starting address is NULL RTEMS INVALID ADDRESS address not on four byte boundary RTEMS TOO MANY too many regions created RTEMS INVALID SIZE invalid page size DESCRIPTION This directive creates a region from a physically contiguous memory space which starts at starting address and is length bytes long Segments al
253. o direct an event set to a target task Based upon the state of the target task one of the following situations applies e Target Task is Blocked Waiting for Events Ifthe waiting task s input event condition is satisfied then the task is made ready for execution Ifthe waiting task s input event condition is not satisfied then the event set is posted but left pending and the task remains blocked e Target Task is Not Waiting for Events The event set is posted and left pending 11 3 2 Receiving an Event Set The rtems_event_receive directive is used by tasks to accept a specific input event con dition The task also specifies whether the request is satisfied when all requested events are available or any single requested event is available If the requested event condition is satisfied by pending events then a successful return code and the satisfying event set are returned immediately If the condition is not satisfied then one of the following situations applies e By default the calling task will wait forever for the event condition to be satisfied e Specifying the RTEMS_NO_WAIT option forces an immediate return with an error status code Chapter 11 Event Manager 117 e Specifying a timeout limits the period the task will wait before returning with an error status code 11 3 3 Determining the Pending Event Set A task can determine the pending event set by calling the rtems_event_receive directive with a value of RTE
254. occupies the non existent state before a rtems_task_create has been issued on its behalf A task enters the non existent state from any other state in the system when it is deleted with the rtems_task_delete directive While a task occupies this state it does not have a TCB or a task ID assigned to it therefore no other tasks in the system may reference this task When a task is created via the rtems_task_create directive it enters the dormant state This state is not entered through any other means Although the task exists in the system it cannot actively compete for system resources It will remain in the dormant state until it is started via the rtems_task_start directive at which time it enters the ready state The task is now permitted to be scheduled for the processor and to compete for other system resources Non existent Creating Deleting gt Starting Deleting Ready Yielding Readying Dispatching Blocking Blocked Blocking Deleting Deleting Non existent 178 RTEMS C User s Guide A task occupies the blocked state whenever it is unable to be scheduled to run A running task may block itself or be blocked by other tasks in the system The running task blocks itself through voluntary operations that cause the task to wait The only way a task can block a task other than itself is with the rtems_task_suspend directive A task enters the blocked state due to any of the following conditions e A tas
255. of the target processor is helpful in understanding some of RT EMS features A thorough understanding of the executive cannot be obtained without studying the entire manual because many of RTEMS concepts and features are interrelated Experienced RTEMS users will find that the manual organization facilitates its use as a reference document 1 10 Conventions The following conventions are used in this manual e Significant words or phrases as well as all directive names are printed in bold type e Items in bold capital letters are constants defined by RTEMS Each language inter face provided by RTEMS includes a file containing the standard set of constants 10 RTEMS C User s Guide data types and structure definitions which can be incorporated into the user appli cation e A number of type definitions are provided by RTEMS and can be found in rtems h e The characters Ox preceding a number indicates that the number is in hexadecimal format Any other numbers are assumed to be in decimal format 1 11 Manual Organization This first chapter has presented the introductory and background material for the RTEMS executive The remaining chapters of this manual present a detailed description of RTEMS and the environment including run time behavior it creates for the user A chapter is dedicated to each manager and provides a detailed discussion of each RTEMS manager and the directives which it provides The presentation format for eac
256. on the value for this field corresponds to the setting of the macro CONFIGURE_MICROSECONDS_PER_TICK If not defined by the applica tion then the CONFIGURE_MICROSECONDS_PER_TICK macro defaults to 10000 10 milliseconds is the number of clock ticks for a timeslice When using the confdefs h mechanism for configuring an RTEMS application the value for this field corresponds to the setting of the macro CONFIGURE_TICKS_PER_TIMESLICE is the maximum number of devices that can be registered When using the confdefs h mechanism for configuring an RTEMS appli cation the value for this field corresponds to the setting of the macro CONFIGURE_MAXIMUM_DEVICES is the maximum number of device drivers that can be registered When using the confdefs h mechanism for configuring an RTEMS application the value for this field corresponds to the setting of the macro CONFIGURE_MAXIMUM_DRIVERS This value is set to maximum_ devices if it is greater than maximum_drivers number of device drivers is the number of device drivers for the system There should be the same number of entries in the Device Driver Table If this field is zero then the User driver address table entry should be NULL When using the confdefs h mechanism for configuring an RTEMS application the value for this field is calculated automatically based on the number of entries in the Device Driver Table This calculation is based on the assumption that the Device Driver Table is named
257. on Table The generated table is named Multiprocessing configuration By default this is not defined CONFIGURE MP NODE NUMBER is the node number of this node in a multiprocessor system The default node number is NODE NUMBER which is set directly in RTEMS test Makefiles CONFIGURE MP MAXIMUM NODES is the maximum number of nodes in a multiproces sor system The default is 2 CONFIGURE MP MAXIMUM GLOBAL OBJECTS is the maximum number of concurrently active global objects in a multiprocessor system The default is 32 CONFIGURE MP MAXIMUM PROXIES is the maximum number of concurrently active thread task proxies in a multiprocessor system The default is 32 CONFIGURE MP MPCI TABLE POINTER is the pointer to the MPCI Configuration Ta ble The default value of this field is amp MPCI table 22 2 5 Classic API Configuration This section defines the Classic API related system configuration parameters supported by confdefs h CONFIGURE MAXIMUM TASKS is the maximum number of Classic API tasks that can be concurrently active The default for this field is 0 CONFIGURE MAXIMUM TIMERS is the maximum number of Classic API timers that can be concurrently active The default for this field is 0 CONFIGURE MAXIMUM SEMAPHORES is the maximum number of Classic API semaphores that can be concurrently active T he default for this field is 0 CONFIGURE MAXIMUM MESSAGE QUEUES is the maximum number of Classic API mes sage queues that ca
258. on designer Alternate term for user provided This term is used to designate any software routines which must be written by the application designer Memory pointers used by the processor to fetch the address of rou tines which will handle various exceptions and interrupts The list of tasks blocked pending the release of a particular resource Message queues regions and semaphores have a wait queue associ ated with them When a task voluntarily releases control of the processor 262 RTEMS C User s Guide Command and Variable Index Command and Variable Index _Internal_errors_What_happened 171 C confdefs hi cere RIS ER sedere ent 215 CONFIGURE APPLICATION NEEDS CLOCK DRIVER PiipeubvePe tqauvaedperdee Peau eda esu 218 CONFIGURE APPLICATION NEEDS CONSOLE DRIVER liiqu4eqe yag phrunddppucv ups EE RE eed reus 217 CONFIGURE_APPLICATION_NEEDS_STUB_DRIVER E E E E EN EA OE E E 218 CONFIGURE_APPLICATION_NEEDS_TIMER_DRIVER mE 218 CONFIGURE EXECUTIVE RAM WORK AREA 217 CONFIGURE EXTRA TASK STACKS 217 CONFIGURE_GNAT_RTEMS 200005 222 CONFIGURE_HAS_OWN_CONFIGURATION_TABLE 217 CONFIGURE HAS OWN DEVICE DRIVER TABLE 217 CONFIGURE HAS OWN INIT TASK TABLE 219 CONFIGURE HAS OWN MOUNT TABLE 216 CONFIGURE HAS OWN MULTIPROCESSING TABLE ice igoewuee deduce neem b de Weald 218 CONFIGURE INIT TASK ARGUMENTS 219 CONFIGURE
259. on enabled and a higher priority task is unblocked as the result of this directive The execution time of this directive is directly related to the number of tasks waiting on the message queue although it is more efficient than the equivalent number of invocations of rtems message queue send Broadcasting a message to a global message queue which does not reside on the local node will generate a request telling the remote node to broadcast the message to the specified message queue When a task is unblocked which resides on a different node from the message queue a copy of the message is forwarded to the appropriate node the waiting task is unblocked and the proxy used to represent the task is reclaimed 110 RTEMS C User s Guide 10 4 7 MESSAGE QUEUE RECEIVE Receive message from a queue CALLING SEQUENCE rtems status code rtems message queue receive rtems id id void buffer size t size uint32 t option set rtems interval timeout 25 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL message received successfully RTEMS INVALID ID invalid queue id RTEMS INVALID ADDRESS buffer is NULL RTEMS INVALID ADDRESS size is NULL RTEMS_UNSATISFIED queue is empty RTEMS TIMEOUT timed out waiting for message RTEMS OBJECT WAS DELETED queue deleted while waiting DESCRIPTION This directive receives a message from the message queue specified in id The RTEMS WAIT and RTEMS NO WAIT options of t
260. on initialize the MPCI e get packet obtain a packet buffer e return packet return a packet buffer e send packet send a packet to another node e receive packet called to get an arrived packet A packet is sent by RTEMS in each of the following situations e an RQ is generated on an originating node e an RR is generated on a destination node e a global object is created e a global object is deleted e a local task blocked on a remote object is deleted e during system initialization to check for system consistency If the target hardware supports it the arrival of a packet at a node may generate an interrupt Otherwise the real time clock ISR can check for the arrival of a packet In any case the rtems multiprocessing announce directive must be called to announce the arrival of a packet After exiting the ISR control will be passed to the Multiprocessing Server to process the packet The Multiprocessing Server will call the get packet entry to obtain a packet buffer and the receive entry entry to copy the message into the buffer obtained 23 3 1 INITIALIZATION The INITIALIZATION component of the user provided MPCI layer is called as part of the rtems initialize executive directive to initialize the MPCI layer and associated hardware It is invoked immediately after all of the device drivers have been initialized This component should be adhere to the following prototype Chapter 23 Multiprocessing Manager 245 rtems_
261. onfiguration Table 2045 234 22 11 Multiprocessor Communications Interface Table 236 22 12 Determining Memory Requirements 200 237 22 13 Sizing the RTEMS RAM Workspace 2045 238 23 Multiprocessing Manager 241 23 1 Introd uetiOn recente EE RR eee auc rU ET eq ae wea 241 23 2 Back eroun ips esce edge does te de DR ERU D Rebates 241 23 2 1 N0de8 oui epe RRRU CEU ERERUREQEROQPER 241 23 2 2 Global Objects scere ree RE RR ERE ceases 242 23 2 3 Global Object Table 00 cece eee eee 242 23 2 4 Remote Operations 0 0 c cece eee ne 242 29 2 0 Proxies sens casa emet esRuer ter eee madonna eae ees 243 23 2 6 Multiprocessor Configuration Table 243 23 3 Multiprocessor Communications Interface Layer 244 23 3 1 INITIALIZATION ssseeeeenRRIRIR e 244 29 9 3 GEI PACKETL leere Debe D nn AE ER e 245 23 3 3 RETURN PACKET uuscscekere aa p des 245 23 34 RECEIVE PACKET 5 eesebeeebepbebb Fete P ex Een 245 23 3 5 SEND PACKET ccs 423 504 wide Wert EC URIDIS e eS 246 23 3 6 Supporting Heterogeneous Environments 246 23 4 OPeratiOns uresen periaate aia Face De Eo o e D dae d 247 23 4 1 Announcing a Packet 0 cece eee eee eee ees 247 23 0 DLCCIVES a ote ados d Beets Ra Toate aban RSS REAL S a atetitius 247 23 5 1 MULTIPROCESSING ANNOUNCE Announce the arriv
262. or more information about the usage of the various data types 3 2 List of Data Types The following is a complete list of the RTEMS primitive data types in alphabetical order rtems_address is the data type used to manage addresses It is equivalent to a void pointer rtems_asr is the return type for an RTEMS ASR rtems_asr_entry is the address of the entry point to an RTEMS ASR rtems_attribute is the data type used to manage the attributes for RTEMS ob jects It is primarily used as an argument to object create routines to specify char acteristics of the new object rtems_boolean may only take on the values of TRUE and FALSE rtems_context is the CPU dependent data structure used to manage the integer and system register portion of each task s context rtems_context_fp is the CPU dependent data structure used to manage the floating point portion of each task s context rtems_device_driver is the return type for a RTEMS device driver routine rtems_device_driver_entry is the entry point to a RTEMS device driver routine rtems_device_major_number is the data type used to manage device major num bers rtems_device_minor_number is the data type used to manage device minor num bers rtems_double is the RTEMS data type that corresponds to double precision floating point on the target hardware rtems_event_set is the data type used to manage and manipulate RTEMS event sets with the Event Manager rtems_extension is
263. or number Write operations typically require a buffer address as part of the argument parameter block The contents of this buffer will be sent to the device NOTES This directive may or may not cause the calling task to be preempted This is dependent on the device driver being invoked 170 RTEMS C User s Guide 16 4 10 IO CONTROL Special device services CALLING SEQUENCE rtems status code rtems io control rtems device major number major rtems device minor number minor void argument J3 DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL successfully initialized RTEMS_INVALID_NUMBER invalid major device number DESCRIPTION This directive calls the device driver I O control routine specified in the Device Driver Table for this major number The exact functionality of the driver entry called by this directive is driver dependent It should not be assumed that the control entries of two device drivers are compatible For example an RS 232 driver I O control operation may change the baud rate of a serial line while an I O control operation for a floppy disk driver may cause a seek operation NOTES This directive may or may not cause the calling task to be preempted This is dependent on the device driver being invoked Chapter 17 Fatal Error Manager 171 17 Fatal Error Manager 17 1 Introduction The fatal error manager processes all fatal or irrecoverable errors The directive provided by the fatal error manag
264. ore were to be known globally then the attribute_set parameter would be RTEMS_GLOBAL RTEMS_PRIORITY 9 2 6 Building a SEMAPHORE OBTAIN Option Set In general an option is built by a bitwise OR of the desired option components The set of valid options for the rtems_semaphore_obtain directive are listed in the following table e RTEMS_WAIT task will wait for semaphore default e RTEMS_NO_WAIT task should not wait Option values are specifically designed to be mutually exclusive therefore bitwise OR and addition operations are equivalent as long as each attribute appears exactly once in the component list An option listed as a default is not required to appear in the list although it is a good programming practice to specify default options If all defaults are desired the option RTEMS_DEFAULT_OPTIONS should be specified on this call This example demonstrates the option parameter needed to poll for a semaphore The option parameter passed to the rtems_semaphore_obtain directive should be RTEMS_NO_ WAIT 9 3 Operations 9 3 1 Creating a Semaphore The rtems_semaphore_create directive creates a binary or counting semaphore with a user specified name as well as an initial count If a binary semaphore is created with a count of zero 0 to indicate that it has been allocated then the task creating the semaphore is considered the current holder of the semaphore At create time the method for ordering waiting tasks in the semaphore s t
265. ot reside on the local node will generate a request to the remote node to obtain a message from the specified message queue If no message is available and RTEMS_WAIT was specified then the task must be blocked until a message is posted A proxy is allocated on the remote node to represent the task until the message is posted A clock tick is required to support the timeout functionality of this directive 112 RTEMS C User s Guide 10 4 8 MESSAGE QUEUE GET NUMBER PENDING Get number of messages pending on a queue CALLING SEQUENCE rtems status code rtems message queue get number pending rtems id id uint32 t count DIRECTIVE STATUS CODES RTEMS SUCCESSFUL number of messages pending returned successfully RTEMS INVALID ADDRESS count is NULL RTEMS INVALID ID invalid queue id DESCRIPTION This directive returns the number of messages pending on this message queue in count If no messages are present on the queue count is set to zero NOTES Getting the number of pending messages on a global message queue which does not reside on the local node will generate a request to the remote node to actually obtain the pending message count for the specified message queue Chapter 10 Message Manager 113 10 4 9 MESSAGE QUEUE FLUSH Flush all messages on a queue CALLING SEQUENCE rtems status code rtems message queue flush rtems id id uint32 t count DIRECTIVE STATUS CODES RTEMS SUCCESSFUL
266. ous A multiprocessor computer system composed of a single type of pro cessor 256 ID IDLE task interface internal address interrupt interrupt level RTEMS C User s Guide An RTEMS assigned identification tag used to access an active ob ject A special low priority task which assumes control of the CPU when no other task is able to execute A specification of the methodology used to connect multiple inde pendent subsystems The address used to access dual ported memory by the node which owns the memory A hardware facility that causes the CPU to suspend execution save its status and transfer control to a specific location A mask used to by the CPU to determine which pending interrupts should be serviced If a pending interrupt is below the current inter rupt level then the CPU does not recognize that interrupt Interrupt Service Routine I O ISR kernel list little endian local local operation logical address loosely coupled major number manager memory pool message An ISR is invoked by the CPU to process a pending interrupt An acronym for Input Output An acronym for Interrupt Service Routine In this document this term is used as a synonym for executive A data structure which allows for dynamic addition and removal of entries It is not statically limited to a particular size A data representation scheme in which the bytes composing a numeric value are arranged
267. period CALLING SEQUENCE rtems status code rtems rate monotonic cancel rtems id id 25 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL period canceled successfully RTEMS INVALID ID invalid rate monotonic period id RTEMS NOT OWNER OF RESOURCE rate monotonic period not created by calling task DESCRIPTION This directive cancels the rate monotonic period id This period will be reinitiated by the next invocation of rtems rate monotonic period with id NOTES This directive will not cause the running task to be preempted The rate monotonic period specified by id must have been created by the calling task Chapter 19 Rate Monotonic Manager 195 19 4 4 RATE MONOTONIC DELETE Delete a rate monotonic period CALLING SEQUENCE rtems status code rtems rate monotonic delete rtems id id DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL period deleted successfully RTEMS_INVALID_ID invalid rate monotonic period id DESCRIPTION This directive deletes the rate monotonic period specified by id If the period is running it is automatically canceled The PCB for the deleted period is reclaimed by RTEMS NOTES This directive will not cause the running task to be preempted A rate monotonic period can be deleted by a task other than the task which created the period 196 RTEMS C User s Guide 19 4 5 RATE MONOTONIC PERIOD Conclude current Start next period CALLING SEQUENCE rtems status code rtems rate monotonic pe
268. plete dominance of software over hardware costs Because of this it is necessary that formal disciplines be established to increase the probability that software is characterized by a high degree of correctness maintainability and portability In addition these disciplines must promote practices that aid in the consistent and orderly development of a software system within schedule and budgetary constraints To be effective these disciplines must adopt standards which channel individual software efforts toward a common goal The push for standards in the software development field has been met with various degrees of success The Microprocessor Operating Systems Interfaces MOSI effort has experienced only limited success As popular as the UNIX operating system has grown the attempt to develop a standard interface definition to allow portable application development has only recently begun to produce the results needed in this area Unfortunately very little effort has been expended to provide standards addressing the needs of the real time community Several organizations have addressed this need during recent years The Real Time Executive Interface Definition RTEID was developed by Motorola with technical input from Software Components Group RTEID was adopted by the VMEbus International Trade Association VITA as a baseline draft for their proposed standard multiprocessor real time executive interface Open Real Time Kernel Interface Defin
269. processing Manager chapter 20 5 1 Tightly Coupled Systems A tightly coupled system is a multiprocessor configuration in which the processors commu nicate solely via shared global memory The MPCI can simply place the RTEMS packets in the shared memory space The two primary considerations when designing an MPCI for a tightly coupled system are data consistency and informing another node of a packet The data consistency problem may be solved using atomic test and set operations to provide a lock in the shared memory It is important to minimize the length of time any particular processor locks a shared data structure The problem of informing another node of a packet can be addressed using one of two techniques The first technique is to use an interprocessor interrupt capability to cause an interrupt on the receiving node This technique requires that special support hardware be provided by either the processor itself or the target platform The second technique is to have a node poll for arrival of packets The drawback to this technique is the overhead associated with polling 20 5 2 Loosely Coupled Systems A loosely coupled system is a multiprocessor configuration in which the processors com municate via some type of communications link which is not shared global memory The MPCI sends the RTEMS packets across the communications link to the destination node The characteristics of the communications link vary widely and have a signif
270. provided handler returns control to RTEMS then the RTEMS default handler will be used This default handler invokes the directive fatal error occurred with the RTEMS_TASK_ EXITTED directive status 21 2 3 8 FATAL Error Extension The FATAL error extension is associated with the fatal error occurred directive If this extension is defined in any static or dynamic extension set and the fatal error occurred directive has been invoked then this extension will be called This extension should have a prototype similar to the following rtems extension user fatal error Internal errors Source the source rtems boolean is internal rtems unsigned32 the error where the error is the error code passed to the fatal error occurred directive This extension is invoked from the fatal error occurred directive If defined the user s FATAL error extension is invoked before RTEMS default fatal error routine is invoked and the processor is stopped For example this extension could be used 210 RTEMS C User s Guide to pass control to a debugger when a fatal error occurs This extension should not call any RTEMS directives 21 2 4 Order of Invocation When one of the critical system events occur the user extensions are invoked in either forward or reverse order Forward order indicates that the static extension set is invoked followed by the dynamic extension sets in the order in which they were created Reverse order means that th
271. r Processing chapter of the Applications Supplement document for a specific target processor 17 3 Operations 17 3 1 Announcing a Fatal Error The rtems_fatal_error_occurred directive is invoked when a fatal error is detected Be fore invoking any user supplied fatal error handlers or the RTEMS fatal error handler the rtems_fatal_error_occurred directive stores useful information in the variable _ Internal_errors_What_happened This structure contains three pieces of information e the source of the error API or executive core e whether the error was generated internally by the executive and a e a numeric code to indicate the error type 172 RTEMS C User s Guide The error type indicator is dependent on the source of the error and whether or not the error was internally generated by the executive If the error was generated from an API then the error code will be of that API s error or status codes The status codes for the RTEMS API are in cpukit rtems include rtems rtems status h Those for the POSIX API can be found in lt errno h gt The rtems_fatal_error_occurred directive is responsible for invoking an optional user supplied fatal error handler and or the RTEMS fatal error handler All fatal error handlers are passed an error code to describe the error detected Occasionally an application requires more sophisticated fatal error processing such as pass ing control to a debugger For these cases a user supplied fatal
272. r has not been used or the last usage of this timer was by the rtems_timer_fire_when or rtems_timer_server_fire_when directive then an error is returned The timer service routine is not changed or fired by this directive 8 3 7 Initiating the Timer Server The rtems_timer_initiate_server directive is used to allocate and start the execution of the Timer Server task The application can specify both the stack size and attributes of the Timer Server The Timer Server executes at a priority higher than any application task and thus the user can expect to be preempted as the result of executing the rtems_timer_ initiate_server directive 8 3 8 Deleting a Timer The rtems_timer_delete directive is used to delete a timer If the timer is running and has not expired the timer is automatically canceled The timer s control block is returned to the TMCB free list when it is deleted A timer can be deleted by a task other than the task which created the timer Any subsequent references to the timer s name and ID are invalid 8 4 Directives This section details the timer manager s directives A subsection is dedicated to each of this manager s directives and describes the calling sequence related constants usage and status codes 74 RTEMS C User s Guide 8 4 1 TIMER_CREATE Create a timer CALLING SEQUENCE rtems_status_code rtems_timer_create rtems_name name rtems_id id DIRECTIVE STATUS CODES RTEMS SUCCESSFUL tim
273. ration Table The Multiprocessor Configuration Table contains information needed by RTEMS when used in a multiprocessor system This table is discussed in detail in the section Multiprocessor Configuration Table of the Configuring a System chapter 244 RTEMS C User s Guide 23 3 Multiprocessor Communications Interface Layer The Multiprocessor Communications Interface Layer MPCI is a set of user provided proce dures which enable the nodes in a multiprocessor system to communicate with one another These routines are invoked by RTEMS at various times in the preparation and processing of remote requests Interrupts are enabled when an MPCI procedure is invoked It is assumed that if the execution mode and or interrupt level are altered by the MPCI layer that they will be restored prior to returning to RTEMS The MPCI layer is responsible for managing a pool of buffers called packets and for sending these packets between system nodes Packet buffers contain the messages sent between the nodes Typically the MPCI layer will encapsulate the packet within an envelope which contains the information needed by the MPCI layer The number of packets available is dependent on the MPCI layer implementation The entry points to the routines in the user s MPCI layer should be placed in the Multi processor Communications Interface Table The user must provide entry points for each of the following table entries in a multiprocessor system e initializati
274. re its priority is raised to the ceiling priority When the task holding the task completely releases the binary semaphore i e not for a nested release the holder s priority is restored to the value it had before any higher priority was put into effect The need to identify the highest priority task which will attempt to obtain a particular semaphore can be a difficult task in a large complicated system Although the priority ceiling algorithm is more efficient than the priority inheritance algorithm with respect to the maximum number of task priority changes which may occur while a task holds a particular semaphore the priority inheritance algorithm is more forgiving in that it does not require this apriori information The RTEMS implementation of the priority ceiling algorithm takes into account the scenario in which a task holds more than one binary semaphore The holding task will execute at the priority of the higher of the highest ceiling priority or at the priority of the highest priority task blocked waiting for any of the semaphores the task holds Only when the task releases ALL of the binary semaphores it holds will its priority be restored to the normal value 9 2 5 Building a Semaphore Attribute Set In general an attribute set is built by a bitwise OR of the desired attribute components The following table lists the set of valid semaphore attributes e RTEMS_FIFO tasks wait by FIFO default e RTEMS_PRIORITY tasks wait b
275. re related directives to access the semaphore NOTES This directive will not cause the running task to be preempted If node is RTEMS SEARCH ALL NODES all nodes are searched with the local node being searched first All other nodes are searched with the lowest numbered node searched first If node is a valid node number which does not represent the local node then only the semaphores exported by the designated node are searched This directive does not generate activity on remote nodes It accesses only the local copy of the global object table 94 RTEMS C User s Guide 9 4 3 SEMAPHORE DELETE Delete a semaphore CALLING SEQUENCE rtems status code rtems semaphore delete rtems_id id 25 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL semaphore deleted successfully RTEMS INVALID ID invalid semaphore id RTEMS ILLEGAL ON REMOTE OBJECT cannot delete remote semaphore RTEMS RESOURCE IN USE binary semaphore is in use DESCRIPTION This directive deletes the semaphore specified by id All tasks blocked waiting to acquire the semaphore will be readied and returned a status code which indicates that the semaphore was deleted The SMCB for this semaphore is reclaimed by RTEMS NOTES The calling task will be preempted if it is enabled by the task s execution mode and a higher priority local task is waiting on the deleted semaphore The calling task will NOT be preempted if all of the tasks that are waiting on
276. riod rtems id id rtems_interval length DIRECTIVE STATUS CODES RTEMS SUCCESSFUL period initiated successfully RTEMS INVALID ID invalid rate monotonic period id RTEMS NOT OWNER OF RESOURCE period not created by calling task RTEMS NOT DEFINED period has never been initiated only possible when period is set to PERIOD STATUS RTEMS TIMEOUT period has expired DESCRIPTION This directive initiates the rate monotonic period id with a length of period ticks If id is running then the calling task will block for the remainder of the period before reinitiating the period with the specified period If id was not running either expired or never initiated the period is immediately initiated and the directive returns immediately If invoked with a period of RTEMS PERIOD STATUS ticks the current state of id will be returned The directive status indicates the current state of the period This does not alter the state or period of the period NOTES This directive will not cause the running task to be preempted Chapter 19 Rate Monotonic Manager 197 19 4 6 RATE_MONOTONIC_GET_STATUS Obtain status information on period CALLING SEQUENCE rtems status code rtems rate monotonic get status rtems id id rtems rate monotonic period status status DIRECTIVE STATUS CODES RTEMS SUCCESSFUL period initiated successfully RTEMS INVALID ID invalid rate monotonic period id RTEMS INVALID
277. riodic execution utilizing a previously created rate monotonic period Once initiated by the rtems_rate_monotonic_period directive the period is said to run until it either expires or is reinitiated The state of the rate monotonic period results in one of the following scenarios e If the rate monotonic period is running the calling task will be blocked for the remainder of the outstanding period and upon completion of that period the period will be reinitiated with the specified period e If the rate monotonic period is not currently running and has not expired it is initiated with a length of period ticks and the calling task returns immediately e If the rate monotonic period has expired before the task invokes the rtems_rate_ monotonic_period directive the period will be initiated with a length of period ticks and the calling task returns immediately with a timeout error status 19 3 3 Obtaining the Status of a Period If the rtems_rate_monotonic_period directive is invoked with a period of RTEMS_PERIOD_ STATUS ticks the current state of the specified rate monotonic period will be returned The following table details the relationship between the period s status and the directive status code returned by the rtems_rate_monotonic_period directive e RTEMS_SUCCESSFUL period is running e RTEMS_TIMEOUT period has expired e RTEMS_NOT_DEFINED period has never been initiated Obtaining the status of a rate monotonic period does not
278. rity inheritance or priority ceiling and the task does not currently hold any other binary semaphores then the task performing the rtems_semaphore_release will have its priority restored to its normal value 9 3 5 Deleting a Semaphore The rtems_semaphore_delete directive removes a semaphore from the system and frees its control block A semaphore can be deleted by any local task that knows the semaphore s ID As a result of this directive all tasks blocked waiting to acquire the semaphore will be readied and returned a status code which indicates that the semaphore was deleted Any subsequent references to the semaphore s name and ID are invalid 90 RTEMS C User s Guide 9 4 Directives This section details the semaphore manager s directives A subsection is dedicated to each of this manager s directives and describes the calling sequence related constants usage and status codes Chapter 9 Semaphore Manager 91 9 4 1 SEMAPHORE_CREATE Create a semaphore CALLING SEQUENCE rtems_status_code rtems_semaphore_create rtems_name name uint32_t count rtems_attribute attribute_set rtems_task_priority priority_ceiling rtems_id id 25 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL semaphore created successfully RTEMS INVALID NAME invalid semaphore name RTEMS INVALID ADDRESS id is NULL RTEMS TOO MANY too many semaphores created RTEMS NOT DEFINED invalid attribute set RTEMS INVALID NUMBER inva
279. rted the initial state of the task is restored from the starting context area in the task s TCB 5 2 3 Task States A task may exist in one of the following five states e executing Currently scheduled to the CPU e ready May be scheduled to the CPU e blocked Unable to be scheduled to the CPU e dormant Created task that is not started e non existent Uncreated or deleted task An active task may occupy the executing ready blocked or dormant state otherwise the task is considered non existent One or more tasks may be active in the system simulta neously Multiple tasks communicate synchronize and compete for system resources with each other via system calls The multiple tasks appear to execute in parallel but actually each is dispatched to the CPU for periods of time determined by the RTEMS scheduling algorithm The scheduling of a task is based on its current state and priority 5 2 4 Task Priority A task s priority determines its importance in relation to the other tasks executing on the same processor RTEMS supports 255 levels of priority ranging from 1 to 255 The data type rtems_task_priority is used to store task priorities Tasks of numerically smaller priority values are more important tasks than tasks of numer ically larger priority values For example a task at priority level 5 is of higher privilege than a task at priority level 10 There is no limit to the number of tasks assigned to the same priority
280. rtems_task_delete_extension thread_delete rtems_task_switch_extension thread_switch rtems_task_begin_extension thread_begin rtems_task_exitted_extension thread_exitted rtems_fatal_extension fatal rtems_extensions_table thread_create thread_start thread_restart thread_delete thread_switch thread_begin thread_exitted is the address of the user supplied subroutine for the TASK_CREATE extension If this extension for task creation is defined it is called from the task_create directive A value of NULL indicates that no extension is provided is the address of the user supplied subroutine for the TASK_START extension If this extension for task initiation is defined it is called from the task_start directive A value of NULL indicates that no extension is provided is the address of the user supplied subroutine for the TASK_RESTART extension If this extension for task re initiation is defined it is called from the task_restart directive A value of NULL indicates that no extension is provided is the address of the user supplied subroutine for the TASK_DELETE extension If this RTEMS extension for task deletion is defined it is called from the task_delete directive A value of NULL indicates that no extension is provided is the address of the user supplied subroutine for the task context switch extension This subroutine is called from RTEMS dispatcher after the current task has been swapped out but before the
281. rty kernel code The contractor and eventually the Government must pay a licensing fee for every copy of the kernel code used in an embedded system The main drawback to this development environment is that the Government does not own nor has the right to modify code contained within the kernel V amp V techniques in this situation are more difficult than if the complete source code were available Responsibility for system failures due to faulty software is yet another area to be resolved under this environment The Guidance and Control Directorate began a software development effort to address these problems A project to develop an experimental run time kernel was begun that will eliminate the major drawbacks of the Ada programming language mentioned above The Real Time Executive for Multiprocessor Systems RTEMS provides full capabilities for management of tasks interrupts time and multiple processors in addition to those features Preface 3 typical of generic operating systems The code is Government owned so no licensing fees are necessary RTEMS has been implemented in both the Ada and C programming languages It has been ported to the following processor families e Intel i386 and above e Motorola MC68xxx e Motorola MC683xx e Motorola ColdFire e ARM e MIPS e PowerPC e SPARC e Hitachi SH e Hitachi H8 300 e Texas Instruments C3x C4x e OpenCores OR32 e UNIX Support for other processor families including RISC
282. s 52 LODo ues ren qnte DIUI er ur redhead 19 time of d y ies er nn 16 19 65 timer cancel i le sv ERES 76 timer create lug ad VE PETS 74 timer delete d pon eed Es 77 tamer fire after ees 78 timer fire when ess 79 timer ident EpL aTa 75 timer initiate server 80 timer rese tiel peer asd en pened 83 timer server fire after 81 timer server fire when 82 timer service routine 19 72 timer service routine entry 19 vector number s s 19 57 STACK CHECKER ON 2 08 c5es Rer Ree 216 266 RTEMS C User s Guide Concept Index Concept Index A add memory to a region 0 142 announce arrival of package 248 announce fatal error eee eee 173 aperiodic task definition 181 Lol ER 121 ASR mode building 0 000 122 ASR vs ISE uc eRerteevecet EE EERRESES 121 asynchronous signal routine suus 121 B binary semaphores eee eee eee 85 Board Support Packages 00000 199 broadcast message to a queue 109 BSP defit seei in 152 9 D 4T 4l EXER 199 DSPSs cses e epe her n EEE evden 199 buffers definition cilio eee 127 C cancela period i sidcme dL bieER eR dn 194 cancel a timer cse s e fenrec P e rw EE raa 76 CLOCK Si eect cece pt iR fates te ARR Re RUE oats 65 Clock tick 39m iai te nade F
283. s is said to be schedulable if all of the tasks can meet their deadlines RMS provides a set of rules which can be used to perform a guaranteed schedulability analysis for a task set This analysis determines whether a task set is schedulable under worst case conditions and emphasizes the predictability of the system s behavior It has been proven that RMS is an optimal static priority algorithm for scheduling independent pre emptible periodic tasks on a single processor RMS is optimal in the sense that if a set of tasks can be scheduled by any static priority algorithm then RMS will be able to schedule that task set RMS bases it schedulability analysis on the processor utilization level below which all deadlines can be met RMS calls for the static assignment of task priorities based upon their period The shorter a task s period the higher its priority For example a task with a 1 millisecond period has higher priority than a task with a 100 millisecond period If two tasks have the same period then RMS does not distinguish between the tasks However RTEMS specifies that when given tasks of equal priority the task which has been ready longest will execute first RMS s priority assignment scheme does not provide one with exact numeric values for task priorities For example consider the following task set and priority assignments Task Period Priority in milliseconds 1 100 Low 2 50 Medium 3 50 Medium 4 25 High
284. s Guide corresponds to the setting of the macro CONFIGURE_MP_MPCI_TABLE_ POINTER If not defined by the application then the CONFIGURE_ MP_MPCI_TABLE_POINTER macro defaults to the address of the table named MPCI_table 22 11 Multiprocessor Communications Interface Table This table defines the set of callouts that must be provided by an Multiprocessor Commu nications Interface implementation When using the confdefs h mechanism for configuring an RTEMS application the name of this table is assumed to be MPCI_table unless the application sets the CONFIGURE_MP_ MPCI_TABLE_POINTER when configuring a multiprocessing system The format of this table is defined in the following C structure typedef struct uint32_t default_timeout in ticks uint32 t maximum packet size rtems mpci initialization entry initialization rtems mpci get packet entry get packet rtems mpci return packet entry return packet rtems mpci send entry send packet rtems mpci receive entry receive packet rtems mpci table default timeout maximum packet size initialization get packet return packet send is the default maximum length of time a task should block waiting for a response to a directive which results in communication with a remote node The maximum length of time is a function the user supplied multiprocessor communications layer and the media used This timeout only applies to directives which would not block if
285. s assumption simply by using the worst case execution time of each task Another assumption is that the tasks are independent This means that the tasks do not wait for one another or contend for resources This assumption can be relaxed by accounting for the amount of time a task spends waiting to acquire resources Similarly each task s execution time must account for any I O performed and any RTEMS directive calls In addition the assumptions did not account for the time spent executing interrupt service routines This can be accounted for by including all the processor utilization by interrupt service routines in the utilization calculation Similarly one should also account for the impact of delays in accessing local memory caused by direct memory access and other processors accessing local dual ported memory The assumption that nonperiodic tasks are used only for initialization or failure recovery can be relaxed by placing all periodic tasks in the critical task set This task set can be scheduled and analyzed using RMS All nonperiodic tasks are placed in the non critical task set Although the critical task set can be guaranteed to execute even under transient overload the non critical task set is not guaranteed to execute In conclusion the application designer must be fully cognizant of the system and its run time behavior when performing schedulability analysis for a system using RMS Every hardware and software factor which impac
286. s the size of the stack for this initialization task initial priority is the priority of this initialization task attribute set is the attribute set used during creation of this initialization task entry point is the address of the entry point of this initialization task mode set is the initial execution mode of this initialization task argument is the initial argument for this initialization task A typical declaration for an Initialization Task Table might appear as follows rtems initialization tasks table Initialization tasks 2 1 INIT 1 NAME 1024 Ly DEFAULT ATTRIBUTES Init 1 DEFAULT MODES 1 Chapter 22 Configuring a System 231 Fs INIT 2 NAME 1024 250 FLOATING POINT Init 2 NO_PREEMPT 2 F 22 8 Driver Address Table The Device Driver Table is used to inform the I O Manager of the set of entry points for each device driver configured in the system The table contains one entry for each device driver required by the application The number of entries is defined in the num ber_of_device_drivers entry in the Configuration Table This table is copied to the Device Drive Table during the IO Manager s initialization giving the entries in this table the lower major numbers The format of each entry in the Device Driver Table is defined in the following C structure typedef struct rtems_device_driver_entry initialization_entry rtems_device_driver_entry open_entry rtems_device_dr
287. s then placed at the front of the queue NOTES The calling task will be preempted if it has preemption enabled and a higher priority task is unblocked as the result of this directive Sending a message to a global message queue which does not reside on the local node will generate a request telling the remote node to post the message on the specified message queue If the task to be unblocked resides on a different node from the message queue then the message is forwarded to the appropriate node the waiting task is unblocked and the proxy used to represent the task is reclaimed Chapter 10 Message Manager 109 10 4 6 MESSAGE QUEUE BROADCAST Broadcast N messages to a queue CALLING SEQUENCE rtems status code rtems message queue broadcast rtems id id void buffer size t size uint32 t count DIRECTIVE STATUS CODES RTEMS SUCCESSFUL message broadcasted successfully RTEMS INVALID ID invalid queue id RTEMS INVALID ADDRESS buffer is NULL RTEMS INVALID ADDRESS count is NULL RTEMS INVALID SIZE invalid message size DESCRIPTION This directive causes all tasks that are waiting at the queue specified by id to be unblocked and sent the message contained in buffer Before a task is unblocked the message buffer of size byes in length is copied to that task s message buffer The number of tasks that were unblocked is returned in count NOTES The calling task will be preempted if it has preempti
288. s_rate_monotonic_create rtems_name name rtems_id id DIRECTIVE STATUS CODES RTEMS SUCCESSFUL rate monotonic period created successfully RTEMS INVALID NAME invalid period name RTEMS TOO MANY too many periods created DESCRIPTION This directive creates a rate monotonic period The assigned rate monotonic id is returned in id This id is used to access the period with other rate monotonic manager directives For control and maintenance of the rate monotonic period RTEMS allocates a PCB from the local PCB free pool and initializes it NOTES This directive will not cause the calling task to be preempted Chapter 19 Rate Monotonic Manager 193 19 4 2 RATE MONOTONIC IDENT Get ID of a period CALLING SEQUENCE rtems status code rtems rate monotonic ident rtems name name rtems id id j DIRECTIVE STATUS CODES RTEMS SUCCESSFUL period identified successfully RTEMS INVALID NAME period name not found DESCRIPTION This directive obtains the period id associated with the period name to be acquired If the period name is not unique then the period id will match one of the periods with that name However this period id is not guaranteed to correspond to the desired period The period id is used to access this period in other rate monotonic manager directives NOTES This directive will not cause the running task to be preempted 194 RTEMS C User s Guide 19 4 3 RATE MONOTONIC CANCEL Cancel a
289. sage If the packet cannot be successfully sent the fatal error manager should be invoked If node is set to zero the packet is to be broadcasted to all other nodes in the system Although some MPCI layers will be built upon hardware which support a broadcast mech anism others may be required to generate a copy of the packet for each node in the system Many MPCI layers use the packet length field of the rtems packet prefix portion of the packet to avoid sending unnecessary data This is especially useful if the media connecting the nodes is relatively slow The to_convert field of the MP packet prefix portion of the packet indicates how much of the packet in rtems_unsigned32 s may require conversion in a heterogeneous system 23 3 6 Supporting Heterogeneous Environments Developing an MPCI layer for a heterogeneous system requires a thorough understanding of the differences between the processors which comprise the system One difficult problem is the varying data representation schemes used by different processor types The most pervasive data representation problem is the order of the bytes which compose a data entity Processors which place the least significant byte at the smallest address are classified as little endian processors Little endian byte ordering is shown below w lt ct o w w ed d o N w ed d oO T w e d o o Conversely processors whic
290. sage to every task waiting on the specified message queue as an atomic operation The message is copied to each waiting task s message buffer and each task is unblocked The number of tasks which were unblocked is returned to the caller 10 3 6 Deleting a Message Queue The rtems_message_queue_delete directive removes a message queue from the system and frees its control block as well as the memory associated with this message queue s message buffer pool A message queue can be deleted by any local task that knows the message queue s ID As a result of this directive all tasks blocked waiting to receive a message from the message queue will be readied and returned a status code which indicates that the message queue was deleted Any subsequent references to the message queue s name and ID are invalid Any messages waiting at the message queue are also deleted and deallocated 102 RTEMS C User s Guide 10 4 Directives This section details the message manager s directives A subsection is dedicated to each of this manager s directives and describes the calling sequence related constants usage and status codes Chapter 10 Message Manager 103 10 4 1 MESSAGE QUEUE CREATE Create a queue CALLING SEQUENCE rtems status code rtems message queue create rtems name name uint32 t count uint32 t max message size rtems attribute attribute set rtems id id DIRECTIVE STATUS CODES RTEMS SUCCESSFUL que
291. sh between the initial rtems_task_start of the task and any ensuing calls to rtems_task_restart of the task This can be beneficial in deleting a task Instead of deleting a task using the rtems_task_delete directive a task can delete another task by restarting that task and allowing that task to release resources back to RTEMS and then delete itself NOTES If id is RTEMS_SELF the calling task will be restarted and will not return from this directive The calling task will be preempted if its preemption mode is enabled and the task being restarted has a higher priority The task must reside on the local node even if the task was created with the RTEMS_GLOBAL option Chapter 5 Task Manager 43 5 4 5 TASK_DELETE Delete a task CALLING SEQUENCE rtems_status_code rtems_task_delete rtems_id id 25 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL task restarted successfully RTEMS INVALID ID task id invalid RTEMS ILLEGAL ON REMOTE OBJECT cannot restart remote task DESCRIPTION This directive deletes a task either the calling task or another task as specified by id RTEMS stops the execution of the task and reclaims the stack memory any allocated delay or timeout timers the TCB and if the task is RTEMS FLOATING POINT its floating point context area RTEMS does not reclaim the following resources region segments partition buffers semaphores timers or rate monotonic periods NOTES A task is responsible for
292. ssage event semaphore or segment with a timeout specified A running task issues a directive which deletes a message queue a semaphore or a region on which the blocked task is waiting A running task issues a rtems_task_restart directive for the blocked task The running task with its preemption mode enabled may be made ready by issuing any of the directives that may unblock a task with a higher priority This directive may be issued from the running task itself or from an ISR A ready task occupies the executing state when it has control of the CPU A task enters the executing state due to any of the following conditions The task is the highest priority ready task in the system The running task blocks and the task is next in the scheduling queue The task may be of equal priority as in round robin scheduling or the task may possess the highest priority of the remaining ready tasks The running task may reenable its preemption mode and a task exists in the ready queue that has a higher priority than the running task The running task lowers its own priority and another task is of higher priority as a result The running task raises the priority of a task above its own and the running task is in preemption mode 180 RTEMS C User s Guide Chapter 19 Rate Monotonic Manager 181 19 Rate Monotonic Manager 19 1 Introduction The rate monotonic manager provides facilities to implement tasks which execute in a periodic fashion The
293. ssage queue broadcast 109 rtems message queue create 103 rtems message queue delete 106 rtems message queue flush 113 rtems message queue get number pending 112 rtems message queue ident 105 rtems message queue receive 110 rtems message queue send 107 RTEMS C User s Guide rtems message queue urgent 108 rtems m d6 s his eea aa nE NE AE IA ER 18 rtems_mp_packet_classes 18 rtems mpci entry er Ren 18 244 rtems mpci get packet entry 18 rtems mpci initialization entry 18 rtems mpci receive packet entry 18 rtems mpci return packet entry 18 rtems mpci send packet entry 18 rtenus mpci table eve E CERIS 18 rtems multiprocessing announce 248 rtems name Ub Sosa heed ee boobed MERE 18 ttems object name ci eer Ree denn 13 ttemns option sees pir ees qa ec DE eue 18 rtems packet prefix sssss 18 rtems partition create sess 129 rtems partition delete 132 rtems partition get buffer 133 rtems_partition_ident 131 rtems_partition_return_buffer 134 rtems_port_create sees 151 rtems port delete ss eeesss 153 rtems port external to internal 154 rtems port ident
294. ssigned a unique non zero node number by the application designer RTEMS assumes that node numbers 242 RTEMS C User s Guide are assigned consecutively from one to the maximum_nodes configuration parameter The node number node and the maximum number of nodes maximum nodes in a system are found in the Multiprocessor Configuration Table The maximum_nodes field and the number of global objects maximum_global_objects is required to be the same on all nodes in a system The node number is used by RTEMS to identify each node when performing remote oper ations Thus the Multiprocessor Communications Interface Layer MPCI must be able to route messages based on the node number 23 2 2 Global Objects All RTEMS objects which are created with the GLOBAL attribute will be known on all other nodes Global objects can be referenced from any node in the system although certain directive specific restrictions e g one cannot delete a remote object may apply A task does not have to be global to perform operations involving remote objects The maximum number of global objects is the system is user configurable and can be found in the maximum_global_objects field in the Multiprocessor Configuration Table The distribution of tasks to processors is performed during the application design phase Dynamic task relocation is not supported by RTEMS 23 2 3 Global Object Table RTEMS maintains two tables containing object information on every node in a
295. ssuming it is compatible with the following prototype rtems_device_driver io_entry rtems_device_major_number major rtems_device_minor_number minor void argument block J The format and contents of the parameter block are device driver and entry point dependent It is recommended that a device driver avoid generating error codes which conflict with those used by application components A common technique used to generate driver specific error codes is to make the most significant part of the status indicate a driver specific code 16 2 7 Device Driver Initialization RTEMS automatically initializes all device drivers when multitasking is initiated via the rtems_initialize_executive directive RTEMS initializes the device drivers by invoking each device driver initialization entry point with the following parameters major the major device number for this device driver minor Zero argument_block will point to the Configuration Table The returned status will be ignored by RTEMS If the driver cannot successfully initialize the device then it should invoke the fatal_error_occurred directive 16 3 Operations 16 3 1 Register and Lookup Name The rtems io register directive associates a name with the specified device i e ma jor minor number pair Device names are typically registered as part of the device driver initialization sequence The rtems io lookup directive is used to determine the major minor number pair associated w
296. stinguish between the original invocation of the task and subse quent invocations The task s stack and control block are modified to reflect their original creation values Although references to resources that have been requested are cleared resources allocated by the task are NOT automatically returned to RTEMS A task cannot be restarted unless it has previously been started i e dormant tasks cannot be restarted All restarted tasks are placed in the ready state 5 3 4 Suspending and Resuming Tasks The rtems_task_suspend directive is used to place either the caller or another task into a suspended state The task remains suspended until a rtems_task_resume directive is issued This implies that a task may be suspended as well as blocked waiting either to acquire a resource or for the expiration of a timer The rtems_task_resume directive is used to remove another task from the suspended state If the task is not also blocked resuming it will place it in the ready state allowing it to once again compete for the processor and resources If the task was blocked as well as suspended this directive clears the suspension and leaves the task in the blocked state Suspending a task which is already suspended or resuming a task which is not suspended is considered an error The rtems_task_is_suspended can be used to determine if a task is currently suspended 5 3 5 Delaying the Currently Executing Task The rtems_task_wake_after directive cr
297. such that the least significant byte is at the lowest address An object which was created with the LOCAL attribute and is ac cessible only on the node it was created and resides upon In a single processor configuration all objects are local The manipulation of an object which resides on the same node as the calling task An address used by an application In a system without memory management logical addresses will equal physical addresses A multiprocessor configuration where shared memory is not used for communication The index of a device driver in the Device Driver Table A group of related RTEMS directives which provide access and con trol over resources Used interchangeably with heap A sixteen byte entity used to communicate between tasks Messages are sent to message queues and stored in message buffers Chapter 26 Glossary 257 message buffer A block of memory used to store messages message queue An RTEMS object used to synchronize and communicate between tasks by transporting messages between sending and receiving tasks Message Queue Control Block A data structure associated with each message queue used by RTEMS to manage that message queue minor number A numeric value passed to a device driver the exact usage of which is driver dependent mode An entry in a task s control block that is used to determine if the task allows preemption timeslicing processing of signals and the interrupt disab
298. t may be registered in the system By default this is set to 20 e CONFIGURE APPLICATION NEEDS CONSOLE DRIVER is defined if the application wishes to include the Console Device Driver This device driver is responsible for 218 RTEMS C User s Guide providing standard input and output using dev console By default this is not defined CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER is defined if the application wishes to include the Clock Device Driver This device driver is responsible for providing a regular interrupt which invokes the rtems clock tick directive By default this is not defined CONFIGURE APPLICATION NEEDS TIMER DRIVER is defined if the application wishes to include the Timer Driver This device driver is used to benchmark execution times by the RTEMS Timing Test Suites By default this is not defined CONFIGURE APPLICATION NEEDS STUB DRIVER is defined if the application wishes to include the Stub Device Driver This device driver simply provides entry points that return successful and is primarily a test fixture By default this is not defined 22 2 4 Multiprocessing Configuration This section defines the multiprocessing related system configuration parameters supported by confdefs h This class of Configuration Constants are only applicable if CONFIGURE MP APPLICATION is defined CONFIGURE HAS OWN MULTIPROCESSING TABLE is defined if the application wishes to provide their own Multiprocessing Configurati
299. t e eter tegis ie didn du Eee eee e REN 149 15 9 1 Creating Port lasse eR er i EE EEDAN 149 15 3 2 Obtaining Port IDS i eee ebbe thu Res 149 15 3 3 Converting an Address sss 150 15 3 4 Deleting a DPMA Port 2 0 150 15 4 Dirf CUlV68Sz i iue eeiam ee eee a ea a eee eee n 150 15 4 1 PORT CREATE Create a port seseseeeseese 151 15 4 2 PORT_IDENT Get ID of a port 152 15 4 3 PORT DELETE Delete a port 153 15 4 4 PORT EXTERNAL TO INTERNAL Convert external to internal address 0 cece nent teen ennes 154 15 4 5 PORT_INTERNAL_TO_EXTERNAL Convert internal to external address i e dese ee oboe etate be bre etw ern 155 OMG ona go ateteese ceed S IRIURE 157 16 1 Introduction i eer nnee RR IOPEET eden Eas 157 16 2 Background iiie reader bee RR Cr E be er RU 157 16 2 1 Device Driver Table 0 cece cece eects 157 16 2 2 Major and Minor Device Numbers Luuuuueuse 158 16 2 3 Device Names 0 cece cence nn 158 16 2 4 Device Driver Environment 0 eee ee eee 158 16 2 5 Runtime Driver Registration 00000 158 16 2 6 Device Driver Interface 159 16 2 7 Device Driver Initialization 00000 00 159 16 3 Operations 4 000024 enUbPERERBPEE G xe eater Peed bees ees 159 16 3 1 Register and Lookup Name 000 eee ee eee 159 16 3 2 Accessing an Device Driver
300. t found DESCRIPTION This directive obtains the region id associated with the region name to be acquired If the region name is not unique then the region id will match one of the regions with that name However this region id is not guaranteed to correspond to the desired region The region id is used to access this region in other region manager directives NOTES This directive will not cause the running task to be preempted Chapter 14 Region Manager 141 14 4 3 REGION DELETE Delete a region CALLING SEQUENCE rtems status code rtems region delete rtems id id 3 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL region deleted successfully RTEMS INVALID ID invalid region id RTEMS RESOURCE IN USE segments still in use DESCRIPTION This directive deletes the region specified by id The region cannot be deleted if any of its segments are still allocated The RNCB for the deleted region is reclaimed by RTEMS NOTES This directive will not cause the calling task to be preempted The calling task does not have to be the task that created the region Any local task that knows the region id can delete the region 142 RTEMS C User s Guide 14 4 4 REGION_EXTEND Add memory to a region CALLING SEQUENCE rtems_status_code rtems_region_extend rtems_id id void starting address uint32 t length 3 DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL region extended successfully RTEMS_INVALID_ADDRESS starting_address is N
301. t list although it is a good programming practice to specify default components If all defaults are desired then RTEMS_DEFAULT_ATTRIBUTES should be used 34 RTEMS C User s Guide This example demonstrates the attribute_set parameter needed to create a local task which utilizes the numeric coprocessor The attribute_set parameter could be RTEMS_FLOATING_ POINT or RTEMS_LOCAL RTEMS_FLOATING_POINT The attribute_set parameter can be set to RTEMS_FLOATING_POINT because RTEMS_LOCAL is the default for all created tasks If the task were global and used the numeric coprocessor then the attribute_set parameter would be RTEMS_GLOBAL RTEMS_FLOATING_POINT 5 2 10 Building a Mode and Mask In general a mode and its corresponding mask is built by a bitwise OR of the desired components The set of valid mode constants and each mode s corresponding mask constant is listed below e RTEMS_PREEMPT is masked by RTEMS_PREEMPT_MASK and enables preemption e RTEMS_NO_PREEMPT is masked by RTEMS_PREEMPT_MASK and disables preemption e RTEMS_NO_TIMESLICE is masked by RTEMS_TIMESLICE_MASK and disables timeslicing e RTEMS_TIMESLICE is masked by RTEMS_TIMESLICE_MASK and enables timeslicing e RTEMS_ASR is masked by RTEMS_ASR_MASK and enables ASR processing e RTEMS_NO_ASR is masked by RTEMS_ASR_MASK and disables ASR processing e RTEMS_INTERRUPT_LEVEL 0 is masked by RTEMS_INTERRUPT_MASK and enables all interrupts e RTEMS_INTERRUPT_LEVEL n is masked by RTEMS
302. tack for interrupts In this case without special assistance every task s stack must include enough space to handle the task s worst case stack usage as well as the worst case interrupt stack usage This is necessary because the worst case interrupt nesting could occur while any task is executing On many processors without dedicated hardware managed interrupt stacks RTEMS man ages a dedicated interrupt stack in software If this capability is supported on a CPU then it is logically equivalent to the processor supporting a separate interrupt stack in hardware Chapter 20 Board Support Packages 201 20 3 Device Drivers Device drivers consist of control software for special peripheral devices and provide a logical interface for the application developer The RTEMS I O manager provides directives which allow applications to access these device drivers in a consistent fashion A Board Support Package may include device drivers to access the hardware on the target platform These de vices typically include serial and parallel ports counter timer peripherals real time clocks disk interfaces and network controllers For more information on device drivers refer to the I O Manager chapter 20 3 1 Clock Tick Device Driver Most RTEMS applications will include a clock tick device driver which invokes the rtems_clock_tick directive at regular intervals The clock tick is necessary if the ap plication is to utilize timeslicing the clock man
303. te If a signal set is sent to a blocked task then the task will remain blocked and the signals will be processed when the task becomes the running task Sending a signal set to a global task which does not reside on the local node will generate a request telling the remote node to send the signal set to the specified task 126 RTEMS C User s Guide Chapter 13 Partition Manager 127 13 Partition Manager 13 1 Introduction The partition manager provides facilities to dynamically allocate memory in fixed size units The directives provided by the partition manager are e rtems_partition_create Create a partition e rtems_partition_ident Get ID of a partition e rtems_partition_delete Delete a partition e rtems_partition_get_buffer Get buffer from a partition e rtems_partition_return_buffer Return buffer to a partition 13 2 Background 13 2 1 Partition Manager Definitions A partition is a physically contiguous memory area divided into fixed size buffers that can be dynamically allocated and deallocated Partitions are managed and maintained as a list of buffers Buffers are obtained from the front of the partition s free buffer chain and returned to the rear of the same chain When a buffer is on the free buffer chain RTEMS uses two pointers of memory from each buffer as the free buffer chain When a buffer is allocated the entire buffer is available for application use Therefore modifying memory that is outside of an
304. te a timer cece eee eee eee eee 77 delete an extension set 2 0 e eee eee 214 deleting task csse pr RES RR REPas 43 device driver interface 00 2 eee eee 159 Device Driver Table 157 231 device drivers esseri eU xr re EE RI medics 157 device haies leni lese Ra t Rr REED RR 158 disable interrupts cemere 61 disabling interrupts 000 58 dispatclillg seng ocium trn err pP TRES 176 dual ported memoty 2er er eene renes 149 dual ported memory definition 149 E enable interr plis i cer e e tele ec i 62 establish an ASR 200 2 eee eee eee ee 124 establish an ISR occu ED etr es nee 60 event condition building 115 event flag definition 0 115 event set building eese e eres 115 event set definition slsleseeeessss 115 EVENS e ma ede RU REB I EE T ET 115 extension Set i2ls 0919 ele 09 rre l1eAl Gls 205 external addresses definition 149 F fatal error detection ccc eee eee 171 fatal error processing 0 004 71 fatal error user extension 000 ee 171 fatal error announce eee eee eee 173 fatalerfOrss i e eere ENRERE 171 fire a task based timer at wall time 82 fire a timer after an interval 78 fire a timer at wall time 79 fir
305. tensions Manager 209 21 2 3 6 TASK BEGIN Extension The TASK_BEGIN extension is invoked when a task begins execution It is invoked imme diately before the body of the starting procedure and executes in the context in the task This user extension have a prototype similar to the following rtems_extension user_task_begin rtems_tcb current_task 25 where current task can be used to access the TCB for the currently executing task which has begun The distinction between the TASK BEGIN and TASK START extension is that the TASK BEGIN extension is executed in the context of the actual task while the TASK START extension is executed in the context of the task performing the task start directive For most extensions this is not a critical distinction 21 2 3 7 TASK EXITTED Extension The TASK_EXITTED extension is invoked when a task exits the body of the starting procedure by either an implicit or explicit return statement This user extension have a prototype similar to the following rtems extension user task exitted rtems tcb current task 23 where current task can be used to access the TCB for the currently executing task which has just exitted Although exiting of task is often considered to be a fatal error this extension allows recovery by either restarting or deleting the exiting task If the user does not wish to recover then a fatal error may be reported If the user does not provide a TASK_EXITTED extension or the
306. ter 16 I O Manager 157 16 I O Manager 16 1 Introduction The input output interface manager provides a well defined mechanism for accessing device drivers and a structured methodology for organizing device drivers The directives provided by the I O manager are e rtems_io_initialize Initialize a device driver e rtems_io_register_name Register a device name e rtems_io_register_driver Register a device name e rtems_io_unregister_driver Unregister a device name e rtems_io_lookup_name Look up a device name e rtems_io_open Open a device e rtems_io_close Close a device e rtems_io_read Read from a device e rtems io write Write to a device e rtems io control Special device services 16 2 Background 16 2 1 Device Driver Table Each application utilizing the RTEMS I O manager must specify the address of a Device Driver Table in its Configuration Table This table contains each device driver s entry points that is to be initialised by RTEMS during initialization Each device driver may contain the following entry points e Initialization e Open e Close e Read e Write e Control If the device driver does not support a particular entry point then that entry in the Config uration Table should be NULL RTEMS will return RTEMS SUCCESSFUL as the executive s and zero 0 as the device driver s return code for these device driver entry points Applications can register and unregister drivers with the RTEMS I O m
307. than the running task NOTES The calling task may be preempted if it causes a higher priority task to be made ready for execution Releasing a global semaphore which does not reside on the local node will generate a request telling the remote node to release the semaphore If the task to be unblocked resides on a different node from the semaphore then the semaphore allocation is forwarded to the appropriate node the waiting task is unblocked and the proxy used to represent the task is reclaimed The outermost release of a local binary priority inheritance or priority ceiling semaphore may result in the calling task having its priority lowered This will occur if the calling task holds no other binary semaphores and it has inherited a higher priority 98 RTEMS C User s Guide 9 4 6 SEMAPHORE_FLUSH Unblock all tasks waiting on a semaphore CALLING SEQUENCE rtems_status_code rtems_semaphore_flush rtems_id id 25 DIRECTIVE STATUS CODES RTEMS SUCCESSFUL semaphore released successfully RTEMS INVALID ID invalid semaphore id RTEMS ILLEGAL ON REMOTE OBJECT not supported for remote semaphores DESCRIPTION This directive unblocks all tasks waiting on the semaphore specified by id Since there are tasks blocked on the semaphore the semaphore s count is not changed by this directive and thus is zero before and after this directive is executed Tasks which are unblocked as the result of this directive will ret
308. the operation were performed locally is the size in bytes of the longest packet which the MPCI layer is capable of sending This value should represent the total number of bytes available for a RT EMS interprocessor messages is the address of the entry point for the initialization procedure of the user supplied multiprocessor communications layer is the address of the entry point for the procedure called by RTEMS to obtain a packet from the user supplied multiprocessor communi cations layer is the address of the entry point for the procedure called by RTEMS to return a packet to the user supplied multiprocessor communica tions layer is the address of the entry point for the procedure called by RTEMS to send an envelope to another node This procedure is part of the user supplied multiprocessor communications layer Chapter 22 Configuring a System 237 receive is the address of the entry point for the procedure called by RTEMS to retrieve an envelope containing a message from another node This procedure is part of the user supplied multiprocessor communications layer More information regarding the required functionality of these entry points is provided in the Multiprocessor chapter 22 12 Determining Memory Requirements Since memory is a critical resource in many real time embedded systems the RTEMS Classic API was specifically designed to allow unused managers to be forcibly excluded from the run time environment This
309. the return type for RTEMS user extension routines rtems_fatal_extension is the entry point for a fatal error user extension handler routine rtems_id is the data type used to manage and manipulate RTEMS object IDs rtems_interrupt_frame is the data structure that defines the format of the inter rupt stack frame as it appears to a user ISR This data structure may not be defined on all ports rtems_interrupt_level is the data structure used with the rtems_interrupt_ disable rtems_interrupt_enable and rtems_interrupt_flash routines This 18 RTEMS C User s Guide data type is CPU dependent and usually corresponds to the contents of the processor register containing the interrupt mask level rtems_interval is the data type used to manage and manipulate time intervals Intervals are non negative integers used to measure the length of time in clock ticks rtems_isr is the return type of a function implementing an RTEMS ISR rtems_isr_entry is the address of the entry point to an RTEMS ISR It is equivalent to the entry point of the function implementing the ISR rtems_mp_packet_classes is the enumerated type which specifies the categories of multiprocessing messages For example one of the classes is for messages that must be processed by the Task Manager rtems_mode is the data type used to manage and dynamically manipulate the exe cution mode of an RTEMS task rtems mpci entry is the return type of an RTEMS MPCI routine rtems
310. the semaphore are remote tasks The calling task does not have to be the task that created the semaphore Any local task that knows the semaphore id can delete the semaphore When a global semaphore is deleted the semaphore id must be transmitted to every node in the system for deletion from the local copy of the global object table The semaphore must reside on the local node even if the semaphore was created with the RTEMS GLOBAL option Proxies used to represent remote tasks are reclaimed when the semaphore is deleted Chapter 9 Semaphore Manager 95 9 4 4 SEMAPHORE OBTAIN Acquire a semaphore CALLING SEQUENCE rtems status code rtems semaphore obtain rtems id id uint32 t option set rtems interval timeout DIRECTIVE STATUS CODES RTEMS SUCCESSFUL semaphore obtained successfully RTEMS UNSATISFIED semaphore not available RTEMS TIMEOUT timed out waiting for semaphore RTEMS OBJECT WAS DELETED semaphore deleted while waiting RTEMS INVALID ID invalid semaphore id DESCRIPTION This directive acquires the semaphore specified by id The RTEMS WAIT and RTEMS NO WAIT components of the options parameter indicate whether the calling task wants to wait for the semaphore to become available or return immediately if the semaphore is not currently available With either RTEMS WAIT or RTEMS NO WAIT if the current semaphore count is positive then it is decremented by one and the semaphore is success
311. the user wishes to define their own Classic API Initialization Tasks Table This table should be named Initialization_tasks By default this is not defined CONFIGURE_INIT_TASK_NAME is the name of the single initialization task defined by the Classic API Initialization Tasks Table By default the value is rtems_build_ name AUA T Vp 2 23 CONFIGURE INIT TASK STACK SIZE is the stack size of the single initialization task defined by the Classic API Initialization Tasks Table By default the value is RTEMS_ MINIMUM STACK SIZE CONFIGURE INIT TASK PRIORITY is the initial priority of the single initialization task defined by the Classic API Initialization Tasks Table By default the value is 1 which is the highest priority in the Classic API CONFIGURE INIT TASK ATTRIBUTES is the task attributes of the single initialization task defined by the Classic API Initialization Tasks Table By default the value is RTEMS DEFAULT ATTRIBUTES CONFIGURE INIT TASK ENTRY POINT is the entry point a k a function name of the single initialization task defined by the Classic API Initialization Tasks Table By default the value is Init CONFIGURE INIT TASK INITIAL MODES is the initial execution mode of the single initialization task defined by the Classic API Initialization Tasks Table By default the value is RTEMS NO PREEMPT CONFIGURE INIT TASK ARGUMENTS is the task argument of the single initialization task defined by the Classic API Ini
312. the value for this field corresponds to the setting of the macro CONFIGURE NUMBER OF INITIAL EXTENSIONS which is set automat ically by confdefs h based on the size of the User Extensions Table is the address of the User Extension Table This table contains the entry points for the static set of optional user extensions If no user extensions are configured then this entry should be NULL The format of this table will be discussed below When using the confdefs h mechanism for configuring an RTEMS applica tion the User Extensions Table is named Configuration Initial Extensions and defined in confdefs h It is initialized based on the following macros e CONFIGURE INITIAL EXTENSIONS e STACK CHECKER EXTENSION The application may configure one or more initial user extension sets by setting the CONFIGURE INITIAL EXTENSIONS macro By defining the STACK CHECKER EXTENSION macro the task stack bounds check ing user extension set is automatically included in the application User multiprocessing table is the address of the Multiprocessor Configuration Table This table contains information needed by RTEMS only when used in a multiprocessor configuration This field must be NULL when RTEMS is used in a single processor configuration When using the confdefs h mechanism for configuring an RTEMS application the Multiprocessor Configuration Table is automatically generated when the CONFIGURE_MP_APPLICATION is defined If CONFIGURE_MP_ A
313. them A well designed real time system can benefit from this architecture by building a rich library of standard application components which can be used repeatedly in other real time projects 1 5 RTEMS Internal Architecture RTEMS can be viewed as a set of layered components that work in harmony to provide a set of services to a real time application system The executive interface presented to the application is formed by grouping directives into logical sets called resource managers Functions utilized by multiple managers such as scheduling dispatching and object man agement are provided in the executive core The executive core depends on a small set of CPU dependent routines Together these components provide a powerful run time en vironment that promotes the development of efficient real time application systems The following figure illustrates this organization E Initialization Task Fatal Error Event Message Dual Ported Memory Partition Subsequent chapters present a detailed description of the capabilities provided by each of the following RTEMS managers 8 RTEMS C User s Guide e initialization e task e interrupt e clock e timer e semaphore e message e event e signal e partition e region e dual ported memory e I O e fatal error e rate monotonic e user extensions e multiprocessing 1 6 User Customization and Extensibility As thirty two bit microprocessors have
314. tialization Tasks Table By default the value is 0 220 RTEMS C User s Guide 22 2 7 POSIX API Configuration The parameters in this section are used to configure resources for the RTEMS POSIX API They are only relevant if the POSIX API is enabled at configure time using the enable posix option e CONFIGURE MAXIMUM POSIX THREADS is the maximum number of POSIX API threads that can be concurrently active The default is 0 e CONFIGURE MAXIMUM POSIX MUTEXES is the maximum number of POSIX API mu texes that can be concurrently active The default is 0 e CONFIGURE MAXIMUM POSIX CONDITION VARIABLES is the maximum number of POSIX API condition variables that can be concurrently active The default is 0 e CONFIGURE MAXIMUM POSIX KEYS is the maximum number of POSIX API keys that can be concurrently active The default is 0 e CONFIGURE MAXIMUM POSIX TIMERS is the maximum number of POSIX API timers that can be concurrently active The default is 0 e CONFIGURE MAXIMUM POSIX QUEUED SIGNALS is the maximum number of POSIX API queued signals that can be concurrently active The default is 0 e CONFIGURE MAXIMUM POSIX MESSAGE QUEUES is the maximum number of POSIX API message queues that can be concurrently active The default is 0 e CONFIGURE MAXIMUM POSIX SEMAPHORES is the maximum number of POSIX API semaphores that can be concurrently active The default is 0 22 2 8 POSIX Initialization Threads Table Configuration The confdefs h con
315. tiprocessor executive is a more realistic model of the outside world or environment for which it is designed As a result the system will always be more logical efficient and reliable By using the directives provided by RTEMS the real time applications developer is freed from the problem of controlling and synchronizing multiple tasks and processors In addi tion one need not develop test debug and document routines to manage memory pass messages or provide mutual exclusion The developer is then able to concentrate solely on the application By using standard software components the time and cost required to develop sophisticated real time applications is significantly reduced 1 4 RTEMS Application Architecture One important design goal of RTEMS was to provide a bridge between two critical layers of typical real time systems As shown in the following figure RTEMS serves as a buffer between the project dependent application code and the target hardware Most hardware dependencies for real time applications can be localized to the low level device drivers Chapter 1 Overview 7 Application Dependent Software Standard Application Components evice RTEMS rivers Target Hardware The RTEMS I O interface manager provides an efficient tool for incorporating these hard ware dependencies into the system while simultaneously providing a general mechanism to the application code that accesses
316. to assign a priority level to each individual task when it is created and to alter a task s priority at run time RTEMS 176 RTEMS C User s Guide provides 255 priority levels Level 255 is the lowest priority and level 1 is the highest When a task is added to the ready chain it is placed behind all other tasks of the same priority This rule provides a round robin within priority group scheduling characteristic This means that in a group of equal priority tasks tasks will execute in the order they become ready or FIFO order Even though there are ways to manipulate and adjust task priorities the most important rule to remember is The RTEMS scheduler will always select the highest priority task that is ready to run when allocating the processor to a task 18 2 2 Preemption Another way the user can alter the basic scheduling algorithm is by manipulating the preemption mode flag RTEMS_PREEMPT_MASK of individual tasks If preemption is disabled for a task RTEMS_NO_PREEMPT then the task will not relinquish control of the processor until it terminates blocks or re enables preemption Even tasks which become ready to run and possess higher priority levels will not be allowed to execute Note that the preemption setting has no effect on the manner in which a task is scheduled It only applies once a task has control of the processor 18 2 3 Timeslicing Timeslicing or round robin scheduling is an additional method which can be used to
317. to be preempted 152 RTEMS C User s Guide 15 4 2 PORT_IDENT Get ID of a port CALLING SEQUENCE rtems_status_code rtems_port_ident rtems_name name rtems id id DIRECTIVE STATUS CODES RTEMS SUCCESSFUL port identified successfully RTEMS INVALID ADDRESS id is NULL RTEMS INVALID NAME port name not found DESCRIPTION This directive obtains the port id associated with the specified name to be acquired If the port name is not unique then the port id will match one of the DPMAs with that name However this port id is not guaranteed to correspond to the desired DPMA The port id is used to access this DPMA in other dual ported memory area related directives NOTES This directive will not cause the running task to be preempted Chapter 15 Dual Ported Memory Manager 153 15 4 3 PORT_DELETE Delete a port CALLING SEQUENCE rtems_status_code rtems_port_delete rtems_id id DIRECTIVE STATUS CODES RTEMS_SUCCESSFUL port deleted successfully RTEMS_INVALID_ID invalid port id DESCRIPTION This directive deletes the dual ported memory area specified by id The DPCB for the deleted dual ported memory area is reclaimed by RTEMS NOTES This directive will not cause the calling task to be preempted The calling task does not have to be the task that created the port Any local task that knows the port id can delete the port 154 RTEMS C User s Guide 15 4 4 PORT_EXTERNAL_TO_INTERNAL Convert e
318. ts the execution time of each task must be accounted for in the schedulability analysis 19 2 4 7 Further Reading For more information on Rate Monotonic Scheduling and its schedulability analysis the reader is referred to the following C L Liu and J W Layland Scheduling Algorithms for Multiprogramming in a Hard Real Time Environment Journal of the Association of Computing Machinery January 1973 pp 46 61 John Lehoczky Lui Sha and Ye Ding The Rate Monotonic Scheduling Algo rithm Exact Characterization and Average Case Behavior IEEE Real Time Sys tems Symposium 1989 pp 166 171 186 RTEMS C User s Guide Lui Sha and John Goodenough Real Time Scheduling Theory and Ada TEEE Computer April 1990 pp 53 62 Alan Burns Scheduling hard real time systems a review Software Engineering Journal May 1991 pp 116 128 19 3 Operations 19 3 1 Creating a Rate Monotonic Period The rtems_rate_monotonic_create directive creates a rate monotonic period which is to be used by the calling task to delineate a period RTEMS allocates a Period Control Block PCB from the PCB free list This data structure is used by RTEMS to manage the newly created rate monotonic period RTEMS returns a unique period ID to the application which is used by other rate monotonic manager directives to access this rate monotonic period 19 3 2 Manipulating a Period The rtems_rate_monotonic_period directive is used to establish and maintain pe
319. ue created successfully RTEMS INVALID NAME invalid queue name RTEMS INVALID ADDRESS id is NULL RTEMS INVALID NUMBER invalid message count RTEMS INVALID SIZE invalid message size RTEMS TOO MANY too many queues created RTEMS_UNSATISFIED unable to allocate message buffers RTEMS MP NOT CONFIGURED multiprocessing not configured RTEMS TOO MANY too many global objects DESCRIPTION This directive creates a message queue which resides on the local node with the user defined name specified in name For control and maintenance of the queue RTEMS allocates and initializes a QCB Memory is allocated from the RTEMS Workspace for the specified count of messages each of max message size bytes in length The RTEMS assigned queue id returned in id is used to access the message queue Specifying RTEMS PRIORITY in attribute set causes tasks waiting for a message to be ser viced according to task priority When RTEMS FIFO is specified waiting tasks are serviced in First In First Out order NOTES This directive will not cause the calling task to be preempted The following message queue attribute constants are defined by RTEMS e RTEMS_FIFO tasks wait by FIFO default e RTEMS PRIORITY tasks wait by priority e RTEMS LOCAL local message queue default e RTEMS GLOBAL global message queue Message queues should not be made global unless remote tasks must interact with the created message queue This
320. ues e Device drivers may be invoked from ISRs e Only local device drivers are accessible through the I O manager e A device driver routine may invoke all other RTEMS directives including I O di rectives on both local and global objects Although the RTEMS I O manager provides a framework for device drivers it makes no assumptions regarding the construction or operation of a device driver 16 2 5 Runtime Driver Registration Board support package and application developers can select wether a device driver is statically entered into the default device table or registered at runtime Dynamic registration helps applications where 1 The BSP and kernel libraries are common to a range of applications for a specific target platform An application may be built upon a common library with all drivers The application selects and registers the drivers Uniform driver name lookup protects the application 2 The type and range of drivers may vary as the application probes a bus during initialization 3 Support for hot swap bus system such as Compact PCI 4 Support for runtime loadable driver modules Chapter 16 I O Manager 159 16 2 6 Device Driver Interface When an application invokes an I O manager directive RTEMS determines which device driver entry point must be invoked The information passed by the application to RTEMS is then passed to the correct device driver entry point RTEMS will invoke each device driver entry point a
321. uler to scan the entire chain to determine which task receives the processor The other method is to schedule the task by placing it in the proper place on the ready chain based on the designated scheduling criteria at the time it enters the ready state Thus when the processor is free the first task on the ready chain is allocated the processor RTEMS schedules tasks using the second method to guarantee faster response times to external events 18 2 Scheduling Mechanisms RTEMS provides four mechanisms which allow the user to impact the task scheduling process e user selectable task priority level e task preemption control e task timeslicing control e manual round robin selection Each of these methods provides a powerful capability to customize sets of tasks to satisfy the unique and particular requirements encountered in custom real time applications Although each mechanism operates independently there is a precedence relationship which governs the effects of scheduling modifications The evaluation order for scheduling characteristics is always priority preemption mode and timeslicing When reading the descriptions of timeslicing and manual round robin it is important to keep in mind that preemption if enabled of a task by higher priority tasks will occur as required overriding the other factors presented in the description 18 2 1 Task Priority and Scheduling The most significant of these mechanisms is the ability for the user
322. urn from the rtems semaphore release directive with a status code of RTEMS_UNSATISFIED to indicate that the semaphore was not obtained This directive may unblock any number of tasks Any of the unblocked tasks may preempt the running task if the running task s preemption mode is enabled and an unblocked task has a higher priority than the running task NOTES The calling task may be preempted if it causes a higher priority task to be made ready for execution If the task to be unblocked resides on a different node from the semaphore then the waiting task is unblocked and the proxy used to represent the task is reclaimed Chapter 10 Message Manager 99 10 Message Manager 10 1 Introduction The message manager provides communication and synchronization capabilities using RTEMS message queues The directives provided by the message manager are e rtems_message_queue_create Create a queue e rtems_message_queue_ident Get ID of a queue e rtems_message_queue_delete Delete a queue e rtems_message_queue_send Put message at rear of a queue e rtems_message_queue_urgent Put message at front of a queue e rtems_message_queue_broadcast Broadcast N messages to a queue e rtems_message_queue_receive Receive message from a queue e rtems_message_queue_get_number_pending Get number of messages pending on a queue e rtems_message_queue_flush Flush all messages on a queue 10 2 Background 10 2 1 Messages A message is a v
323. ve a prototype similar to the following rtems extension user task start rtems tcb current task rtems tcb started task 25 where current task can be used to access the TCB for the currently executing task and started task can be used to access the T CB for the dormant task being started This extension is invoked from the task start directive after started task has been made ready to start execution but before it is placed on a ready TCB chain 208 RTEMS C User s Guide 21 2 3 3 TASK RESTART Extension The TASK_RESTART extension directly corresponds to the task_restart directive If this extension is defined in any static or dynamic extension set and a task is being restarted then the extension should have a prototype similar to the following rtems extension user task restart rtems tcb current task rtems tcb restarted task where current task can be used to access the TCB for the currently executing task and restarted task can be used to access the TCB for the task being restarted This extension is invoked from the task restart directive after restarted task has been made ready to start execution but before it is placed on a ready TCB chain 21 2 3 4 TASK DELETE Extension The TASK DELETE extension is associated with the task delete directive If this extension is defined in any static or dynamic extension set and a task is being deleted then the extension routine will automatically be invoked by RT EMS The e
324. ved 23 3 3 RETURN_PACKET The RETURN PACKET component of the user provided MPCI layer is called when RTEMS needs to release a packet to the free packet buffer pool This component should be adhere to the following prototype rtems_mpci_entry user_mpci_return_packet rtems_packet_prefix packet where packet is the address of a packet If the packet cannot be successfully returned the fatal error manager should be invoked 23 3 4 RECEIVE PACKET The RECEIVE PACKET component of the user provided MPCI layer is called when RTEMS needs to obtain a packet which has previously arrived This component should be adhere to the following prototype rtems mpci entry user mpci receive packet rtems packet prefix packet 246 RTEMS C User s Guide where packet is a pointer to the address of a packet to place the message from another node If a message is available then packet will contain the address of the message from another node If no messages are available this entry packet should contain NULL 23 3 5 SEND_PACKET The SEND_PACKET component of the user provided MPCI layer is called when RTEMS needs to send a packet containing a message to another node This component should be adhere to the following prototype rtems_mpci_entry user_mpci_send_packet rtems_unsigned32 node rtems packet prefix packet 25 where node is the node number of the destination and packet is the address of a packet which containing a mes
325. xtension should have a prototype similar to the following rtems extension user task delete rtems tcb current task rtems tcb deleted task 35 where current task can be used to access the TCB for the currently executing task and deleted task can be used to access the TCB for the task being deleted This extension is invoked from the task delete directive after the TCB has been removed from a ready TCB chain but before all its resources including the TCB have been returned to their respective free pools This extension should not call any RTEMS directives if a task is deleting itself current task is equal to deleted task 21 2 3 5 TASK SWITCH Extension The TASK SWITCH extension corresponds to a task context switch If this extension is defined in any static or dynamic extension set and a task context switch is in progress then the extension routine will automatically be invoked by RTEMS The extension should have a prototype similar to the following rtems extension user task switch rtems tcb x current task rtems tcb heir task where current task can be used to access the TCB for the task that is being swapped out and heir_task can be used to access the TCB for the task being swapped in This extension is invoked from RTEMS dispatcher routine after the current task context has been saved but before the heir task context has been restored This extension should not call any RTEMS directives Chapter 21 User Ex
326. xternal to internal address CALLING SEQUENCE rtems_status_code rtems_port_external_to_internal rtems_id id void external void internal i DIRECTIVE STATUS CODES RTEMS INVALID ADDRESS internal is NULL RTEMS SUCCESSFUL successful conversion DESCRIPTION This directive converts a dual ported memory address from external to internal represen tation for the specified port If the given external address is invalid for the specified port then the internal address is set to the given external address NOTES This directive is callable from an ISR This directive will not cause the calling task to be preempted Chapter 15 Dual Ported Memory Manager 155 15 4 5 PORT_INTERNAL_TO_EXTERNAL Convert internal to external address CALLING SEQUENCE rtems_status_code rtems_port_internal_to_external rtems_id id void internal void external J3 DIRECTIVE STATUS CODES RTEMS_INVALID_ADDRESS external is NULL RTEMS_SUCCESSFUL successful conversion DESCRIPTION This directive converts a dual ported memory address from internal to external represen tation so that it can be passed to owner of the DPMA represented by the specified port If the given internal address is an invalid dual ported address then the external address is set to the given internal address NOTES This directive is callable from an ISR This directive will not cause the calling task to be preempted 156 RTEMS C User s Guide Chap
327. y the signal manager are used to service signals A term used to describe a task that has been unblocked and may be scheduled to the CPU A data representation scheme in which the bytes composing a numeric value are arranged such that the most significant byte is at the lowest address A data encoding scheme in which each bit in a variable is used to represent something different This makes for compact data repre sentation A physically contiguous area of memory The task state entered by a task which has been previously started and cannot continue execution until the reason for waiting has been satisfied To simultaneously send a message to a logical set of destinations see Board Support Package Board Support Package buffer calling convention A collection of device initialization and control routines specific to a particular type of board or collection of boards A fixed length block of memory allocated from a partition The processor and compiler dependent rules which define the mecha nism used to invoke subroutines in a high level language These rules define the passing of arguments the call and return mechanism and the register set which must be preserved Central Processing Unit chain This term is equivalent to the terms processor and microprocessor A data structure which allows for efficient dynamic addition and removal of elements It differs from an array in that it is not limited to a predefine
328. y be preempted if its preemption mode is enabled and it lowers its own priority or raises another task s priority Setting the priority of a global task which does not reside on the local node will generate a request to the remote node to change the priority of the specified task If the task specified by id is currently holding any binary semaphores which use the priority inheritance algorithm then the task s priority cannot be lowered immediately If the task s priority were lowered immediately then priority inversion results The requested lowering of the task s priority will occur when the task has released all priority inheritance binary semaphores The task s priority can be increased regardless of the task s use of priority inheritance binary semaphores 48 RTEMS C User s Guide 5 4 10 TASK_MODE Change the current task mode CALLING SEQUENCE rtems_status_code rtems_task_mode rtems_mode mode_set rtems_mode mask rtems_mode previous_mode_set js DIRECTIVE STATUS CODES RTEMS SUCCESSFUL task mode set successfully RTEMS INVALID ADDRESS previous mode set is NULL DESCRIPTION This directive manipulates the execution mode of the calling task A task s execution mode enables and disables preemption timeslicing asynchronous signal processing as well as specifying the current interrupt level To modify an execution mode the mode class es to be changed must be specified in the mask parameter and the desired mod
329. y priority e RTEMS_BINARY_SEMAPHORE restrict values to 0 and 1 e RTEMS_COUNTING_SEMAPHORE no restriction on values default e RTEMS_SIMPLE_BINARY_SEMAPHORE restrict values to 0 and 1 do not allow nested access allow deletion of locked semaphore e RTEMS_NO_INHERIT_PRIORITY do not use priority inheritance default e RTEMS_INHERIT_PRIORITY use priority inheritance e RTEMS_PRIORITY_CEILING use priority ceiling e RTEMS_NO_PRIORITY_CEILING do not use priority ceiling default e RTEMS_LOCAL local task default e RTEMS_GLOBAL global task Attribute values are specifically designed to be mutually exclusive therefore bitwise OR and addition operations are equivalent as long as each attribute appears exactly once in the component list An attribute listed as a default is not required to appear in the attribute list although it is a good programming practice to specify default attributes If all defaults are desired the attribute RTEMS_DEFAULT_ATTRIBUTES should be specified on this call This example demonstrates the attribute_set parameter needed to create a local semaphore with the task priority waiting queue discipline The attribute_set parameter passed to the rtems_semaphore_create directive could be either RTEMS_PRIORITY or RTEMS_LOCAL 88 RTEMS C User s Guide RTEMS_PRIORITY The attribute_set parameter can be set to RTEMS_PRIORITY because RTEMS_LOCAL is the default for all created tasks If a similar semaph
330. y the application code which invoked the rtems_clock_tick directive The timer can be used to implement watchdog routines which only fire to denote that an application error has occurred The timer is reset at specific points in the application to insure that the watchdog does not fire Thus if the application does not reset the watchdog timer then the timer service routine will fire to indicate that the application has failed to reach a reset point This use of a timer is sometimes referred to as a keep alive or a deadman timer 8 2 3 Timer Server The Timer Server task is responsible for executing the timer service routines associated with all task based timers This task executes at a priority higher than any RTEMS application task and is created non preemptible and thus can be viewed logically as the lowest priority interrupt By providing a mechanism where timer service routines execute in task rather than interrupt space the application is allowed a bit more flexibility in what operations a timer service 72 RTEMS C User s Guide routine can perform For example the Timer Server can be configured to have a floating point context in which case it would be safe to perform floating point operations from a task based timer Most of the time executing floating point instructions from an interrupt service routine is not considered safe However since the Timer Server task is non preemptible only directives allowed from an ISR can be
331. y then use system calls to synchronize itself with an application task The synchronization may involve messages events or signals being passed by the ISR to the desired task Directives invoked by an ISR must operate only on objects which reside on the local node The following is a list of RTEMS system calls that may be made from an ISR e Task Management Although it is acceptable to operate on the RTEMS SELF task e g the currently executing task while in an ISR this will refer to the interrupted task Most of the time it is an application implementation error to use RTEMS_SELF from an ISR rtems_task_get_note rtems_task_set_note rtems_task_suspend rtems_task_resume e Clock and Timer Management rtems clock get rtems_clock_tick rtems timer fire after rtems timer fire when rtems timer cancel e Message Event and Signal Management rtems message queue send rtems message queue urgent rtems event send rtems signal send e Semaphore Management rtems semaphore release e Dual Ported Memory Management rtems port external to internal rtems port internal to external e IO Management The following services are safe to call from an ISR if and only if the device driver service invoked is also safe The IO Manager itself is safe but the invoked driver entry point may or may not be rtems io initialize rtems io open rtems io close rtems io read rtems io write rtems io contro
332. zation An RTEMS based application is initiated or re initiated when the processor is reset This initialization code is responsible for preparing the target platform for the RTEMS applica tion Although the exact actions performed by the initialization code are highly processor and target dependent the logical functionality of these actions are similar across a variety of processors and target platforms Normally the application s initialization is performed at two separate times before the call to rtems_initialize_executive reset application initialization and after rtems_initialize_executive in the user s initialization tasks local and global appli cation initialization The order of the startup procedure is as follows 1 Reset application initialization 2 Call to rtems_initialize_executive 3 Local and global application initialization The reset application initialization code is executed first when the processor is reset All of the hardware must be initialized to a quiescent state by this software before initializing RTEMS When in quiescent state devices do not generate any interrupts or require any servicing by the application Some of the hardware components may be initialized in this code as well as any application initialization that does not involve calls to RTEMS directives The processor s Interrupt Vector Table which will be used by the application may need to be set to the required value by the reset applicatio

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