Department of Electrical Engineering Eindhoven University of
Contents
1. means zero or more times the enclosed Parameters are QUEUE the processor queue of the process especially for multiprocessor systems The queues have conventionally the names READYQ queue of processes which can be executed by any processor PROCAQ queue of the first processor PROCBQ queue of the second processor and so on PRI priority of the process HL hardware stacksize for the process SL software stacksize for the process PROCESS NAME name of the process to be started and parameters conform the process heading Processes can remove themselves by executing the BYE statement The following standard processes are already predeclared PROCESS ERRORLOG CHARBUF This process receives error messages from the predeclared buffer ERRORBUF and places them character after character in CHARBUF CHARBUF must be a buffer for messages of the type ASCII or BYTE PROCESS TTIN CHARBUF This process receives characters from a terminal and places them in CHARBUF The terminal must be on addresses 177560 177562 status data registers and vectored via addresses 60 62 PROCESS TTUIT CHARBUF This process receives characters from CHARBUF and sends them to a terminal The terminal must be on addresses 177564 177566 status data registers and vectored via addresses 64 66 Semaphores and regions For synchronisation purposes PAP is extended with the type SEMAF representing a semaphore On this type three operations exist PROCEDUR2. A fatal error results in a BYE for the offending process unless the H switch is set to continue after fatal error Fatal error 90 also stops the process which executes the START statement Auxiliary types routines and statements Some types routines and statements are added to PAP for convenience of the user The types are ADDRESS and WORD which can be treated as integer Two routines for addressing virtual memory locations are available PROCEDURE WRITEREG PART INTEGER REG ADDRESS CONT WORD FUNCTION READREG PART INTEGER REG ADDRESS WORD These can be used to write or read data resp to or from a virtual address In case of write CONT gives the data to be written The virtual address is split in two parts and constructed with the formula PART x 21 REG or in words PART gives the highest 3 bits of the address and REG the lowest 13 The following two routines are written to allow conversion from strings to integers and vice versa PROCEDURE ENTEGERTOSTRING I INTEGER STRING S PROCEDURE STRINGTOINTEGER STRING S VAR I INTEGER INTEGERTOSTRING converts an integer to a string The converted integer is placed in the string with preceding blanks if necessary A sign is always placed in the string If the string can t contain the converted integer an error message is generated STRINGTOINTEGER converts a string to an integer Blanks in the string are ignored only a sign and digits are allowed For all other characters
3. description of the purpose of the various types variables procedures and functions can be found in appendix E Appendix B Pascal plus user manual PASCAL PLUS USER MANUAL Summary This manual describes the extensions and limitations of Pascal plus PAP compared with Pascal Contents Summary Contents Introduction Process Semaphores and regions Messages and buffers Error handling Auxiliary types routines and statements An implementation ODO MQ A Duw NN EP How to use Pascal plus Introduction Pascal plus PAP is a language based on Pascal described in 1 PAP is intended as a programming language for parallel processes For this purpose the language Pascal is extended with some communication and synchronisation primitives This manual describes the extensions of PAP as compared to Pascal Also some system dependent features are described These are all based on Ericsson Pascal 2 a dialect of Pascal 1 K Jensen N Wirth Pascal User Manual amp Report Springer Verlag 1975 2 S Torstendahl Pascal User Manual LM Ericsson l Process To admit parallel processes PAP is extended with the special symbol PROCESS Processes are treated the same way as procedures so can have parameter lists etc It is however not allowed to call processes A process must be started with a START statement This statement is of the form START QUEUE PRI HL SL PROCESS NAME process parameters where
4. INTEGER a hulptype ADDRESS WORD a hulptype QUEUE RECORD SLOT WORD GET PDPT END defines a queue in which a process can reside when sleeping or runnable The fields have the following meaning SLOT used for gaining access to the queue SLOT O means a process is operating on the queue SLOT 1 means no process is operating on the queue initial value SLOT 1 GET points to the first process descriptor in the queue SEMAF RECORD SLOT WORD CTR INTEGER GET PDPT END defines a semaphore The fields mean SLOT see under QUEUE CTR the semaphore counter initially 0 GET see under QUEUE REGION SEMAF defines a region The implementation is analogue to SEMAF the function is different REGION variables have initially CTR 1 MSGBUF RECORD EMPTY SEMAF FULL SEMAF s MUTEX SEMAF LENGTH INTEGER NBYT INTEGER GETPT INTEGER PUTPT INTEGER BUF ARRAY 0 1 oF array 0 1 or BYTE END defines RECEIVE EMPTY FULL 3 MUTEX LENGTH NBYT GETPT PUTPT BUF 3 ERRORBUF TYPE a buffer to be used in the declarations of SEND and The fields have the following meaning Semaphore whose counter gives the number of free places in the buffer Semaphore whose counter gives the number of full places in the buffer Semaphore used to create a mutual exclusion for the buffer access l holds the number of messages that fits in the buffer holds the width of a message for the bu
5. generate an error message with one extra parameter Parameter description NR the number of the error to be generated KIND defines the seriousness of the error 1 fatal 2 warning 4 message PARAM the parameter displayed in the error message e g offending value Called procedures and functions WRERROR Calling procedures and functions STRINGTOINTEGER Suggestions for extensions none Further remarks The procedure can be used in RSX programs too E 29 Description of the procedure PHOENIX Heading PROCEDURE PHOENIX VAR PROCAQ QUEUE VAR PROCBQ QUEUE VAR READYQ QUEUE Task of the procedure Placing the main program in the readyqueue The main program is supposed to do no 1 0 Filling a data area with its APR s registers 3 4 6 memory management register O and the processorqueues Creating the trap routines for TRAP TO O 4 10 14 20 24 250 Map the virtual addresses 0 17777B to the corresponding absolute addresses Copying the setup routine for the other processors to a part of the commen memory that is addressable with memory management diabled This routine initializes the APR s and registers of a processor and gives the processor its own processor queue address wakes the first process and initializes the trap interrupt vectors with the addresses of the interrupt routines Parameter description PROCAQ the processor bound queue for one processor PROCBQ the processor bound
6. none Calling procedures and functions SPSABW Suggestions for extensions none Further remarks none E 40 Description of the procedure SEND Heading PROCEDURE SEND VAR PDPOINTER PDPT VAR MSG UNIV ARRAY INTEGER OF BYTE VAR MBUF UNIV MESBUF Task of the procedure placing a message in a buffer Parameter description PDPOINTER pointer to the process descriptor of the calling process MSG the message to be transported MBUF the buffer where the message is send to Galled procedures and functions WAIT SIGNAL COPYTO Calling procedures and functions WRERROR Suggestions for extensions none Farther remarks The procedure uses the reserved word UNIV Therefore we are not bounded by the array lengths dectared in the heading Description of the procedure SIGNAL Heading PROCEDURE SIGNAL VAR SEM SEMAF Task of the procedure If there are processes sleeping in the semaphore queue one of them is awoken and placed in its processor queue Otherwise the semaphore counter is incremented Parameter description SEM the semaphore which must be signalled Called procedures and functions SPSABW BSARPS QOUT QENTER Calling procedures and functions SEND RECEIVE ATIMAC in the generated interrupt service routine Suggestions for extensions none Further remarks none E 42 Description of the procedure SIMPLEERROR Heading PROCEDURE SIMPLEERROR NR INTEGER KIND INTEGER Task of the pr
7. On the heap all dynamically with NEW created variables are placed The heap grows upward Global variables are always addressed via R3 local variables via R4 In all other cases there is a link via which one can go back in the access chain There is another chain which indicates the sequence in which procedures were called so that upon leaving a procedure all the stackspace used in that procedure e g from declared variables can be released In the software stack the compiler reserves space for all variables To this space 1000 words are added This extra space is used for the heap temporary results parameter copies at procedure calls both chains extra variables created by recursive procedure calls The software stack can be extended with an option of the RSX taskbuilder TKB ref 12 Besides a software stack there is also a hardware stack Here R6 points to top of stack The hardware stack is among others used to save return addresses when calling a subroutine The hardware stack can be extended 12 HIDDEN VARIABLES PROGRAM POR R3 PROCEDURE P PROCEDURE Q BEGIN END PROCEDURE R BEGIN Q END BEGIN R END BEGIN P END R4 R5 8 R3 Fig 2 Example of the stack structure Stack after the calling sequence PAR P R gt Q 13 with the TKB option STACK ref 12 Further details concerning the implementation of Pascal and the addressing mechanism can be foun
8. descriptor and new process stacks Saving the registers R4 R5 R6 the linenumber and the pdpointer on the software stack Changing R5 and R6 to the new created stacks Initializing the field NR of the new process descriptor Parameter QID description pointer to the processor queue of the process for which a _ process descriptor is made priority of that process size of the hardware stack to be created size of the software stack to be created Called procedures and functions CHREG NEWCHK Calling procedures and functions none Suggestions for extensions none Further remarks The user process START is replaced by NEWSTK and a call of the process to be started by PAP Description of the procedure OVFLCEK Heading PROCEDURE OVFLCHK Task of the procedure Testing if a process hardware or software stack overflow occurs Parameter description none Called procedures and functions WRERROR Calling procedures and functions INIT Suggestions for extensions none Further remarks If hardware stack overflow occurs an error 91 fatal is generated If software stack overflow occurs an error 92 fatal is generated The procedure uses the copy of the pdpointer in the local memory The call of OVFLCHK is inserted after each procedure or function dealaration E 28 Description of the procedure PARAMERROR Heading PROCEDURE PARAMERROR NR INTEGER KIND INTEGER PARAM INTEGER Task of the procedure
9. illegal character is found no figure sign or blank The ascii value of the character is given Error 95 Warning This error means that during the conversion of a string to an integer in STRINGTOINTEGER overflow occured This integer is set to MAXINT or MININT depends on the sign Error 96 Warning This error means that the string given as parameter to INTEGERTOSTRING cannot contain the converted integer sign The string is filled with blanks E 10 Description of the procedures and functions The next pages all give a description of a procedure or function The following data are given Heading Task of the procedure function Parameter description Called procedures and functions Calling procedures and functions Suggestions for extensions Further remarks Under Called procedures and functions no standard functions are mentioned E 11 Description of the procedure ATTACH Heading PROCEDURE ATTACH DEV ADDRESS VAR SEM SEMAF Task of the procedure attach a signal on a semaphore to an interrupt vector description address of the interrupt vector the semaphore that must be signalled by an interrupt Parameter DEV SEM Called procedures and functions ATIMAC Calling procedures and functions none Suggestions for extensions Limit the value of DEV to 777B max No higher interrupt vectors exist Further remarks The space for the interrupt service routine is created on the hea
10. procedures and functions QLEAVE SIGNAL Suggestions for extensions none Further remarks see under QLEAVE E 35 Description of the function READREG Heading FUNCTION READREG PART INTEGER REG ADDRESS WORD Task of the function reading a virtual memory address the contents of the address is the function result Parameter description PART tells in which part of 4k words we want to read PART 0 between O and 4k etc REG Gives an address inside these 4k words 13 bit READREG contents of the address represented as an integer Called procedures and functions none Calling procedures and functions none Suggestions for extensions a better way for parameter transport Further remarks If the function result is between O and 77 777B it is represented between O and 32767 Values between 100 OOOB and 177 777B are represented between 32768 and l resp For this reason the address is splitted in two parts Description of the procedure RECEIVE Heading PROCEDURE RECEIVE VAR PDPOINTER PDPT VAR MSG UNIV ARRAY inrecER OF CHAR VAR MBUF UNIV MESBUF Task of the procedure receiving a message from a buffer Parameter description PDPOINTER pointer to the process descriptor of the calling process MSG contains after procedure execution the received message MBUF _ the buffer where the message is received from Called procedures and functions WAIT SIGNAL COPYFROM Calling procedures and functio
11. queue for the other processor READYQ the queue which can be used by both processors Remark the procedure is written for two processors Called procedures and functions WAKEUP QENTER Calling procedures and functions none the procedure is called in the main program inserted by PAP E30 Suggestions for extensions none Further remarks The trap routines for traps to 0 4 10 14 20 24 250 place the address of the trap vector in RO and execute a HALT instruction in KERNEL mode If the routines are proceeded with the console ODT command P a RTI is executed Remember that RO is destroyed at that moment The start address of processor A is at the moment 20100 that of processor B 20200 E 31 Description of the procedure QENTER Heading PROCEDURE QENTER VAR Q QUEUE VAR PDPOINTER PDPT Task of the procedure Placing a process in a queue with slotword according to the priority of the process Parameter description Q queue in which the process is going to be placed PDPOINTER pointer to the process descriptor of the process that must be queued Called procedures and functions BSARPS SPSABW QIN Calling procedures and functions SIGNAL RETTOM PHOENIX Suggestions for extensions none Further remarks QIN places a process in a queve without paying attention to the slotword QENTER does pay attention to the slotword E 32 Description of the procedure QIN Heading PROCEDURE QIN VAR
12. with the language Pascal The formal deseription of this language can be found in the Pascal User Manual amp Report ref 1 Ref 2 is a good introduction to Pascal for those who are not familiar with programming in high level languages 1 Description of the existing hard and software Presently the hardware of the multiprocessor system consists of two LSI 11 23 processors described in ref 3 with 4k words of local memory each and with several CPU bound I 0 devices The CPU s have access to a common memory of 96k words This access is controlled by an arbiter who can grant the common memory to a CPU during one bus cycle fig 1 It is possible to expand the system with more processors and more common memory blocks each controlled by a separate arbiter A more comprehensive description of the hardware configuration can be found in ref 4 Ref 5 describes the arbiter in detail In the group Measurement and Control several Pascal compilers are available There is chosen to use the Ericsson compiler for a description of the deviations from Pascal see ref 6 because that is the one best known within the group the source is available and there exists already some software for the multiprocessor system written in that language e g ref 7 Furthermore there are no important reasons to switch to another compiler The compiler works under the operating system RSX ref 8 9 10 et al This is the reason that this operating s
13. 144 Department of Electrical Engineering Eindhoven University of Technology Eindhoven The Netherlands Group Measurement and Control PASCAL FOR PARALLEL PROCESSES AN IMPLEMENTATION ON A MULTIPROCESSORSYSTEM by F J H M Meulenbroeks Submitted in partial fulfillment of the requirements for the degree of ir M Sc The work was carried out under directorship of prof ir F J Kylstra Advisor ir C A M van den Brekel The Department of Electrical Engineering of the Eindhoven University of Technology does not accept responsibility for the content of this report Summary This report describes the design and implementation of a Pascal system as a programming language for parallel processes on a multiprocessor configuration This configuration consists of two LSI 11 23 processors which operate on a common memory The Pascal system developed is rather flexible modular and easy to maintain It is however rather dependent on the Pascal compiler used Restrictions and suggestions for extensions of the system are also mentioned Contents 5 Summary Contents Preface Introduction Description of the existing hard and software 1 1 Deseription of the hardware configuration 1 2 Description of the existing software Problem analysis and structure of the system 2 1 Design considerations 2 2 General description of the structure of the system 2 3 Alternatives to implement the pr
14. 75 J Welsh J Elder Introduction to Pascal Prentice Hall 1979 Microcomputer processor handbook Digital Equipment corp Maynard Mass 1980 M J Kanters Hardware for a Multiprocessor system with LSI 1l In Proceedings of the Digital Equipment Computer Users Society volume I Europe 1979 P J J M Mostert Het vervangen van de LSI 11 03 CPU door een LSI 11 23 CPU in het multiprocessorsysteem van de vakgroep ER stageverslag THE Eindhoven 1981 S Torstendahl Pascal User Manual LM Ericsson F J H M Meulenbroeks Sequential Pascal met synchronisatieprimitieven als real time taal voor parallelle processen stageverslag THE Eindhoven 1980 8 Introduction to RSX 11 M Digital Equipment corp Maynard Mass 10 il 12 13 14 15 16 17 RSX 11 M M plus MCR operations manual Digital Equipment Corp Maynard Mass 1979 RSX 11 Utilities Manual Digital Equipment corp Maynard Mass 1979 W P M den Dekker Ontwikkeling van een software pakket voor een multiprocessor systeem stageverslag THE Eindhoven 1979 RSX 11 M M plus Task builder manual Digital Equipment corp Maynard Mass 1979 W de Vries An implementation of the language Pascal for the PDP 11 series based on a portable Pascal compiler Verslag doctoraalopdracht THT 1975 U Ammann Die Entwicklung eines Pascal Compilers nach der Methode des Structurierten Programmieren Diss ETH 5456 Z rich 1976 U Ammann On co
15. E WAIT VAR SEM SEMAF delays the calling process if the semaphore counter is zero otherwise decrements this counter by one PROCEDURE SIGNAL VAR SEM SEMAF If no process is delayed in the semaphore queue the semaphore counter is incremented otherwise the process with highest priority is placed in its processor queue Processes with equal priority are awoken on a first come first served basis PROCEDURE ATTACH DEV ADDRESS VAR SEM SEMAF An interrupt service routine is generated which couples a signal on semaphore SEM to an interrupt vectored via address DEV ATTACH doesn t enable or disable interrupts Also the type REGION is implemented This type can be used to protect critical sections A critical section can be made with a REGENTER statement This statement is of the form REGENTER region variable statement statement REGEXIT region variable where region variable is a variable of the type REGION Only one process at a time can be in a REGENTER statement with a certain region name en Warning Nested REGENTER statements with the same region variable create a deadlock Messages and buffers For communication between processes PAP is extended with the types MESSAGE and MSGBUF Variables of the MESSAGE type must be declared as MESSAGE nrofelements OF elementtype l where elementtype may be INTEGER CHAR ASCII or BYTE and nrofelements represents the number of elements of the message Variables declared as MESSAGE can be treated as ARRA
16. GET PDPT VAR PDPOINTER PDPT Task of the procedure Placing a process in a queue according to the priority of the process Parameter description GET pointer to the first process descriptor in the queue PDPOINTER pointer to the process descriptor of the process that must be queued Called procedures and functions none Calling procedures and functions QENTER CHANGE Suggestions for extenstons none Further remarks none E 33 Description of the procedure QLEAVE Heading PROCEDURE QLEAVE VAR Q QUEUE VAR PDPOINTER PDPT Task of the procedure wake a process from a queue with slotword Parameter description Q queue from which a process is going to be awoken PDPOINTER pointer to the process descriptor which is removed from the queue Called procedures and functions SPSABW BSARPS QOUT Calling procedures and functions WAKEUP Suggestions for extensions none Further remarks QOUT wakes a process without paying attention to the slotword QLEAVE does pay attention to the slotword If after execution PDPOINTER nil the queue is empty E 34 Description of the procedure QOUT Heading PROCEDURE QOUT VAR GET PDPT VAR PDPOINTER PDPT Task of the procedure wake a process from a queue Parameter description GET pointer to the first process descriptor in the queue PDPOINTER pointer to the process descriptor which is removed from the queue Called procedures and functions none Calling
17. ININT 100000B Numbers between 32769 and 65535 and between 32769 and 65535 are not changed into MAXINT resp MININT but in the number read before Multiple attempts result in a system trap All these errors are caused by errors in the routine RDI which can be found in the file PIIRDI MAC in PACLIB PAC The routine RDI is changed and all errors mentioned above are corrected The compiler doesn t detect a missing semicolon between an assignment statement and an IF or WHILE statement other statements not investigated It is nearly impossible to read an array of characters from file TTY else than character for character Using 32768 in ones program gives the compiler error 203 integer constant exceeds range I l Appendix I Modifications made in the vracticumsysteem At the THE a course Procescomputersystemen is given ref 20 227 age Parallel to this course students can write software for a small process computer system usually called practicumsysteem as exercise During the last years this software was written in assembler for the multi processor system It is intended to use the Pascal system for that purpose A try out and demonstration version of the practicumsysteem is already written ref 7 This demonstration program is used as test program during the development of the Pascal system This led to the detection of some minor errors in the demonstration program Also some greater improvements were made The
18. NTEGERTOSTRING READREG WRITEREG NEWSTK OVFLCHK NEWCHK INITTOS TTIN TTUIT ERRORLOG replacing the word PROCESS with PROCEDURE inserting a call of INIT as first process statement checking the type compatibility of messages and buffers in SEND and RECEIVE calls inserting PDPOINTER as the first parameter of procedures declared as SYSTEM procedures or functions replacing of the word CYCLE with WHILE TRUE DO BEGIN replacing of the word REGENTER with BEGIN WAIT replacing of the word REGEXIT with SIGNAL END checking if regions are nested correct placing a region arourid each NEW statement if no CYCLE occurs addition of a call of BYE at the end of each process within each process inserting the declaration of a local variable PDPOINTER gt inserting a call of OVFLCHK as first statement of each procedure inserting a call of NEWCHK after each call of NEW replacing the user declaration MSGBUF n OF with the appropriate MSGBUF declaration and initializing this buffer replacing the user declaration MESSAGE n OF with ARRAY 0 n 1 OF A 2 inserting some statements to provide the main program with a process stack replacing the user call of START with a call of NEWSIK followed by a call of the process Around these calls a region is placed A more comprehensive description of the preprocessor is to be given in TH report of W J M Lemmens which is under preparation gt p
19. T 0 nrofelements 1 OF elementtype Variables of the MSGBUF type must be declared as MSGBUF nrofelements OF messagetype nrofelements is the number of messages that can be placed in the buffer of the MSGBUF type On messages and buffers two procedures operate PROCEDURE SEND MESSAGE BUFFER PROCEDURE RECEIVE MESSAGE BUFFER which place resp receive the message in resp from the buffer The types of the message and the buffer elements must match Error handling All runtime error messages are placed in the standard buffer ERRORBUF which is of the type ERRORBUFTYPE This is a buffer which can contain 10 messages of the type ERRORMES array fo 29 OF BYTE Errors can be printed by declaring a character buffer and starting the processes ERRORLOG and TTUIT with this buffer as mrameter Preferably these processes should be started first l Some new error messages are implemented namely 90 fatal stack overruns heap or vice versa Too many NEW statements or too much stackspace reserved in START statements 91 fatal local hardware stack overflow 10 words left 92 fatal local software stack overflow 40 words left 94 warning illegal character in string parameter of STRINGTOINTEGER zero taken as conversion result Error message displays the offending value 95 warning overflow in STRINGTOINTEGER MAXINT or MININT taken dependent on sign 96 warning string in INTEGERTOSTRING too small filled with blanks
20. by the taskbuilder resides on the own account or on LJ The letters RW denote that one wants to use the common for both read and write D 1 Appendix D Structure of the local memory The local memory can be divided into three parts addresses 0 777 These addresses are used for interrupt vectors Most of it however is not used All current devices have a vector address lt 377 addresses 772 1220 These addresses are used by the runtime system They can be subdivided as follows 5 772 774 776 1040 1000 1100 1040 1150 1100 1220 1150 contains the linenumber of the line in execution contains the address of the processorqueue of that processor contains the pdpointer of the process currently being executed Kernel hardware stack Used during interrupt service routines created with ATTACH and during traps caused by an error User hardware stack Used during idling when trying to get a process from a queue for execution software stack during idling software stack during interrupt service routines addresses 1220 17777 Free for user applications and future system extensions Appendix E Software description Introduction New types New variables New runtime errors Description of the procedures and functions Description of the standard processes E 2 E 3 E 7 E 9 E 10 E 49 E 2 Introduction This appendix gives the implementation details of the system All new t
21. cedures and functions none Calling procedures and functions BSARPS Suggestions for extensions _ none Further remarks none E 15 Description of the procedure BWAIT Heading PROCEDURE BWAIT VAR SLOT WORD Task of the procedure Making the processor priority 7 Waiting until there is a 1 in the slotword and make it zero in an indivisible action Parameter description SLOT variable which must be made zero _ Called procedures and functions none Calling procedures and functions SPSABW Suggestions for extensions none Further remarks none E 16 Description of the procedure BYE Heading PROECEDURE BYE VAR PDPOINTER PDPT Task of the procedure Stop the execution of the calling process Parameter description PDPOINTER Process descriptor of the calling process Called procedures and functions SPSABW CHANGE Calling procedures and functions WRERR OR Suggestions for extensions Create the possibility to restart a process that has executed a BYE Further remarks The procedure places the process in the BYEQUEUE from which processes never awake E 16A Description of the procedure CHANGE Heading PROCEDURE CHANGE VAR SLOT WORD VAR GET PDPT Task of the procedure Place the calling process in a queue release the queue and wake a new process Parameter description SLOT word which controls access to the queue in which the calling process must be placed GET
22. d in ref 13 whilst ref 14 15 16 and 17 describe the ETH compiler on which the Ericsson compiler is based 2 5 Choice of an alternative First lets compare the advantages and disadvantages of both alternatives to implement Pascal processes on a multiprocessor system l Processes are separate programs which communicate via external variables Problem is the creation of a common data area This can happen via a COMMON ref 12 Then the software stack must be split in a common and a private part This can only be done by changing the compiler In the common part of the stack the common variables and the heap are placed Also provisions have to be made to take care that all processes place a global variable with a certain name on the same address 2 There is one program in which the statement PROCESS is known This creates the possibility of two sub alternatives A There is a separate stack created in the main stack for each process This implies that we ourselves must take care for stack overflow B Every process gets an own stack This implies a modification of the compiler whereas NEW may also cause problems Alternative 2A has been chosen because no compiler modification is needed for this so no concession towards the design constraints has to be made Remark the reserved word PROCESS is interpreted by the preprocessor This alternative however has the restriction that NEW becomes a critical operation and therefore has to be pr
23. de generation in a Pascal compiler ETH Z rich 1976 U Ammann The Z rich Implementation In Pascal The language and its Implementation D W Barron editor J Wiley 1981 p 63 82 U Ammann Code generation for a Pascal Compiler In Pascal The Language and its Implementation D W Barron editor J Wiley 1981 p 83 124 22 18 R H Eckhouse L R Morris Minicomputer systems Prentice Hall 1979 19 H J M van Kruysdijk Een filesysteem voor een multiprocessor configuratie afstudeerverslag THE Eindhoven 1981 20 F J Kylstra Procescomputersystemen dictaat bij het college nr 5 335 0 THE Eindhoven 1979 A 1 Appendix A Description of the function of the preprocessor The preprocessor transforms a program source written in Pascal plus PAP User manual see appendix B into a file which can be compiled by the Ericsson Pascal compiler The operational characteristics of the preprocessor are addition of the declarations of the PAP standard and system types WORD ADDRESS PDPT QPOINTER PRODESC QUEUE SEMAF REGION MESBUF ERRORMES ERRORBUFTYPE addition of the declaration of the standard and system variables PDPOINTER R5 PROCAQ PROCBQ READYQ BYEQUEUE NUMBER TEMPQPNTR TOPOFSTACK NEWREG STARTREG ERRORBUF addition of the declaration of the standard and system procedures functions and processes INITIALIZE PHOENIX SIGNAL WAIT ATTACH INIT BYE SEND RECEIVE STRINGTOINTEGER I
24. e now created task can be executed Appendix C Generating a device common We want to create a device common with which we can address the whole I O page in a program This can be done as follows First create a data area of 4k words This can be realized with the following program IONEW MAC TITLE IONEW PSECT IONEW BLKW 4095 END This program is translated with the MACRO compiler MAC IONEW IONEW Taskbuilding of the common goes as follows TKB TKB gt IONEW HD PI IONEW IONEW IONEW IKB gt ENTER OPTIONS IKB gt STACK 0 TKB PAR IONEW 0 20000 IKB gt underlined parts are RSX responses PI means the common is position independent HD means give the task file no header STACK 0 means we don t want a stack and PAR IONEW 0 20000 means that the program must be loaded into partition IONEW starting at virtual address 0 and that the partition size is 20000 The common is now created If we want the common to be placed over the I O page we must create a partition IONEW over the I O page and fill this partition with our common Creating a partition can be done with the privileged MCR command ref 9 SET MAIN IONEW 7600 200 DEV The created partition can be initialized by running the task made by TKB IONEW TSK One can address the device common in a program if one gives the taskbuilder as option C 2 RESCOM IONEW RW or COMMON IONEW RW dependent on whether the file IONEW STB made
25. e routine WRERROR E 49 Description of the standard processes Some processes will nearly always be used To make the use of the system more convenient for a user a few of these processes are already implemented as standard processes All of them have reentrant code so they can be started multiple times On the following pages these processes are described in the same way the procedures and functions are described although somewhat more comprehensive Because processes can t have calling procedures and functions that section is omitted 5 50 Description of the standard process TIIN Heading PROCESS TTIN VAR CHARBUF UNIV CHBUFTYPE Task of the process The process reads characters from the console terminal address 177 562B The highest bit of each byte is ignored so all characters are of the type ASCII The characters read are placed in the buffer CHARBUF which is a process parameter Errors of the interface from which the characters are read are ignored Parameter description CHARBUF A buffer where all characters received from the interface are send to The buffer should have messages of one element of type ASCII or BYTE Called procedures and functions ATTACH l WRI TEREG WAIT SEND READREG Suggestions for extensions none Further remarks The process assumes that the interface from which the characters are received has its status register at address 177 560B and its data register at address 177 562B Also t
26. e should contain more line numbers which of course is impossible To avoid this a small compiler modification is made see appendix F so that linenumbers are saved in a location in the local memory instead of the hidden variable This hidden variable is now used to store the address of ERRORBUF 19 5 Limitation d_suggesti for tension e m The implemented system has some limitations in it The known ones will be described here shortly A possible solution is also given The total amount of memory which can be used by the system is limited to 24k words 4k local memory 4k I 0 page This is because at the moment there exists no possibility for overlaying Perhaps this can be realized with the already designed file system ref 19 It is impossible to delete processes completely and return the used memory to the system This could possibly be solved by a good overlaying mechanism as well It is impossible ta change the size of the process stacks dynamically Again overlaying could realize this feature Some more standard routines could be implemented e g read write date time l Programming could be simplified by implementing a multiprocessor version of the symbolic debugger A PAP compiler could speed up and simplify the compiling and task building Also the implementation of the standard types can be hidden for the user The system is slow compared to the system written in assembler This is ca
27. em during starting The priority of a process This must be supplied by the user during starting The magnitude of the priority has influence on the place in a queue where a process is placed see next paragraph A limit for the software stackpointer below which it may not grow because otherwise another stack may be overwritten A limit for the hardware stackpointer below which it may not grow because otherwise another stack may be overwritten A pointer to another process descriptor This pointer is used when the process is in a queue see next paragraph 15 If a process is sleeping or runnable its process descriptor resides in a queue Such a queue consists of a slotword with which the exclusive right of admission to the queue is realised and a pointer to a process descriptor Because each process descriptor contains a pointer to a process descriptor we can make queues as long as necessary If a process has to be queued its process descriptor will be placed in the queue in such a way that all succeding processes have a lower priority whilst all preceding processes have a higher or equal priority The pointer of the queue thus always points to the process descriptor with highest priority that is placed in the queue In cases that the highest priority is not uniquely defined the process descriptor of the process with highest priority which is longest resident in the queue is taken as first queue element If a proc
28. es The software is rather flexible with regard to hardware changes Some changes however need a small software modification These are for the most common cases mentioned below The hardware can be expanded with another processor The software system must then be extended with a processor queue for this new processor This queue must be declared in the texts inserted by the preprocessor and in the system software Also the procedure INITIALIZE must be extended to initialize this new queue Finally PHOENIX must be modified to give the new processor its own initialization routine This also implies that the constant NROFPROCESSORS must be updated and that the new queue must be a parameter of PHOENIX so that the declaration and call of PHOENIX inserted by the preprocessor must be changed too It is also possible to change the amount of local memory given to each processor In that case the constants BEGPAR and BEGADR from PHOENIX must be changed Also in PHOENIX the APRs via which the local memory is mapped must be initialized properly The TKB option STACK should be given the size of the local memory in words when taskbuilding a task for the multiprocessor system H 1 Appendix H Some remarks on Pascal During the development of the system some errors in the Ericsson Pascal compiler are detected These are reported here Some of these errors are already reported earlier ref 7 but will be included here too Because character a
29. ess is removed from a queue it is always the process standing in front of the queue As a programmer of the multiprocessor Pascal system one mostly wants to address the I O page The part of the memory with physical addresses 760000 777776 which contains the device registers Normally one cannot address the I O page in ones program A user of the multisystem however perhaps wants to do I O This is realized by placing a device common over the I O page see ref 12 and appendix C When building a task one can link this common into the task This makes the 1 0 page in assembler addressable through addresses 160000 177776 35 Addressing the local memory Because a program is loaded under RSX it can be placed anywhere in the memory due to the normally present memory management It is therefore not self evident that virtual address 0 corresponds with physical address QO In fact this will never happen because the lower part of the memory is used by the executive A multisystem programmer however wants to use the vector addresses and perhaps the local memory too Therefore we have 16 to interfere with the memory management The memory management is described in ref 18 p 86 88 and 255 259 and in ref 3 chapter 9 The operation of the memory management is supposed to be known for the rest of this paragraph We want virtual address 0 to correspond with absolute address 0 Therefore we have to change APR O Problem is that norma
30. ffer in bytes pointer to the first filled bufferplace pointer to the first free bufferplace the buffer itself The type is used in the declarations of SEND and RECEEVE with the reserved word UNIV which suppresses typechecking so the bounds of BUF have no meaning RECORD EMPTY SEMAF FULL SEMAF MUTEX SEMAF LENGTH INTEGER NBYT INTEGER GETPT INTEGER PUTPT INTEGER BUF ARRAY o 9 OF ERRORMES END E 6 defines the type of an errorbuffer All fields have the same meaning as in MESBUF except that BUF defines a buffer of 10 error messages type ERRORMES ERRORMES ARRAY 0 29 OF CHAR defines an error message These have the following format PAPRUN ERROR nn mmmmm vvvvv where nn error number mmmmm linenumber where the error occurred not correct if the error occurs in a part of the program where the runtime check option R is switched off offending value error 12 and 94 only E 7 New variables Some variables are needed for implementation purposes Here a description of these variables is given PDPOINTER PDPT This variable is added to each process and to the main program It is used as a pointer to the process descriptor of the process in which it is declared This gives a process the possibility to refer to its own process descriptor R5 INTEGER Used to store the value of register 5 temporary when another process is started PROCAQ PROCBQ READYQ BYEQUEUE QPOINTER Po
31. fset is added contains the first byte to copy TOT address where the first byte is copied to OFFSET hulp variable to create the address of the first byte to copy NROFBYTES contains how many bytes must be copied Called procedures and functions none Calling procedures and functions RECEIVE Suggestions for extensions none Further remarks none B 19 Description of the procedure COPYTO Heading PROCEDURE COPYTO VAR FROM CHAR VAR TOT CHAR OFFSET INTEGER NROFBY TES INTEGER Task of the procedure Copying nrofbytes bytes from address from to address tottoffset Parameter description FROM address of the first byte to copy TOT address where when offset is added the first byte is copied to OFFSET hulp variable to create the address where the first byte must be copied to NROFBYTES contains how many bytes must be copied Called procedures and functions none Calling procedures and functions SEND Suggestions for extensions none Further remarks none E 20 Description of the procedure IEBW Heading PROCEDURE IEBW VAR ERRORBUF ERRORBUFTYPE Task of the procedure Initializing 2 R3 with the address of ERRORBUF Parameter description ERRORBUF buffer where all errormessages are send to Called procedures and functions none Calling procedures and functions INITIALIZE Suggestions for extensions none Further remarks In Ericsson Pascal the hidden variable 2 R3 is used for sto
32. he interface must be vectored via address 60B Estimated hardware stacksize required is 15 words Estimated software stacksize required is 70 words The process is CPU bound E 51 Description of the standard process TTUIT Heading PROCESS TTUIT VAR CHARBUF UNIV CHBUFTYPE Task of the process The process writes characters to the console terminal address 177 566B All bits are transmitted The characters which are written are received from the buffer CHARBUF which is a process parameter If a carriage return is received from the buffer a linefeed is automatically added Parameter deseription CHARBUF A buffer where all characters which are written are received from The buffer should have messages of one element of type ASCII CHAR or BYTE Called procedures and functions ATTACH WRITEREG RECEIVE WAIT Suggestions for extensions none Further remarks The process assumes that the interface to which the characters are written has its status register at address 177 564B and its data register at address 177 566B Also the interface must be vectored via address 64B Estimated hardware stacksize is 15 words Estimated software stacksize is 70 words The process is CPU bound E 52 Description of the standard process ERRORLOG Heading PROCESS ERRORLOG VAR BUF UNIV CHBUFTYPE Task of the process The process receives error messages from the buffer ERRORBUF These messages are split into characters which are send t
33. he process is in execution on one of the processors running The process waits for execution on one of the processors runnable The process isn t ready for execution because it is waiting for data a signal of a semaphore access of a region or because it is completely inactive sleeping A process which is runnable waits for execution in a queue A processor which is released because the process it was executing has become sleeping should continue the first process in the queue Processes that are sleeping because they are waiting for a semaphore a region or data from a buffer stay in a queue the so called semaphore queue present with any semaphore region and buffer Because I O devices are CPU bound we must distinguish between processes which do and those which don t use an I O device The latter can be executed on any processor in the system whilst the former are CPU bound Due to this difference there are several queues in which runnable processes must wait for execution If a process is CPU bound it will wait in the queue of the processor it is bound to the processorqueue Otherwise it will wait in the readyqueue A processor which is released gives priority to the processes waiting in its processorqueue If such a process is absent a process waiting in the readyqueue will be continued To implement simultaneously running processes written in Pascal these fundamentally different possibilities e
34. he variable TOPOFSTACK E 24 Description of the procedure INTEGERTOSTRING Heading PROCEDURE INTEGERTOSTRING I INTEGER STRING S Task of the procedure Converting an integer to a string array of CHAR or part of it Parameter description I integer to be converted S conversion result Called procedures and funcions SIMPLEERROR Calling procedures and functions none Suggestions for extensions none Further remarks The conversion result is always preceded by a sign If there is more space in the string than needed the conversion result is filled with preceding blanks If the string cannot contain the converted integer sign an error message 96 is generated The string is filled with blanks E 25 Description of the procedure NEWCHK Heading PROCEDURE NEWCHK TOPOFSTACK INTEGER Task of the procedure Testing if the software stack and the heap overrun eachother Parameter deseription TOPOFSTACK contains the address which represents the top of the software stack Called procedures and functions WRERROR Calling procedures and functions NEWSTK Suggestions for extensions none Further remarks If an error occurs an error message 90 fatal is generated The procedure is called after every NEW inserted by PAP E 26 Description of the procedure NEWSTK Heading PROCEDURE NEWSTK QID QPOINTER PRI INTEGER HL INTEGER SL INTEGER Task of the procedure Generating a new process
35. in the string an error message is generated In case of overflow an error message is generated too Both procedures use the string parameter implementation of Ericsson Pascal PAP is extended with the CYCLE statement to allow processes to repeat themselves infinitely The statement is of the form CYCLE statement statement END The statements in the CYCLE statement are repeated infinitely The CYCLE statement if used must be the last statement of a process declaration Also the CYCLE statement may not occur in other statements e g IF statements This is done because integers 15 bit sign bit can t be interpreted as addresses 16 bit easily An implementation PAP is implemented on a multiprocessor system with two LSI 11 23 s with shared memory The implementation is based on the Ericsson Pascal compiler All previously described procedures are made for this configuration The implementation is however not conform the previous descriptions The following modifications are made Structured types can t have messages buffers or semaphores as elements Arrays with these elements can be declared with the type VECTOR which is of the form VECTOR 1b hb OF elementtype where elementtype can be semaphore message or buffer A vector can be treated as an array with lower bound lb and upper bound ub Type checking for procedures functions and processes is suppressed when the type of a procedure function or process parameter is p
36. inters to the queue of processor A processor B the readyqueue which contains the processes that can be executed by any processor and the byequeue where all processes are placed that have executed a BYE NUMBER INTEGER Contains the number of processes started Used to initialize the process descriptor field NR TEMPPDPT PDPT Temporary pdpointer used when creating a new process descriptor TOPOFSTACK INTEGER Points to the top of the space claimed on the software stack Used when generating new stacks and during error checking NEWREG REGION Region to protect the hidden variable 8 R3 which points to the top of the heap E 8 STARTREG REGION Region to protect the variables R5 and TEMPPDPT when starting a process ERRORBUF ERRORBUF TYPE The standard buffer in which all error messages are placed New runtime errors A few new runtime errors are implemented Their meaning is explained below Error 90 Fatal This error means that the heap and the software stack overrun each other Too many variables are created with NEW or too much stack space is claimed for process stacks Error 91 Fatal This error means that a hardware stack overflow can occur Usually caused by too many recursive procedure calls Error 92 Fatal This error means that a local software stack overflow can occur Error 94 Warning This error means that during the conversion of a string to an integer in STRINGTOINTEGER an
37. lly part of the task is mapped via this APR Normally the first part of the task is a task header about 274B words in size Next in virtual memory comes the hardware stack accessed via R6 SP Usually the size of this stack is lk words The size can be extended with the TKB option STACK The header is not necessary when we have left RSX so it may be overwritten If we now enlarge the stack with say 4k words so part of the stack is mapped via APR 1 we can change APR O so that it points to the lowest 4k words PAR O 0 PDR O 77406B This makes the lowest 4k words addressable via addresses 0 177777 The structure of the local memory can be found in appendix D 17 4 Error handling 4 1 Detecting an error Most of the errors which can occur are detected by the Pascal runtime system The implemented extensions involve some new error causes process hardware stack overflow process software stack overflow heap overruns process stack or new started process overlaps heap in STRINGTOINTEGER one tries to convert a string containing illegal characters the string to be converted in STRINGTOINTEGER doesn t fit in the integer overflow the integer to be converted in INTEGERTOSTRING doesn t fit in the string too small The third error can only appear after a call of NEW or after the creation of new process stacks Every time this error can arise the error conditions are checked and if necessary an er
38. m to be developed must at least be capable to carry out all tasks which are performed by the already existing system written in assembler for a description see ref 11 All software will as far as possible be written in Pascal This will cause the system to be slower and use more memory However it will be easier to write debug and document the software Later on it is always possible to write the software or part of it in assembler if this is desired Procedures should preferably perform only one task The system to be developed doesn t have to support the Pascal standard system routines which refer to RSX routines e g read write get put etc eta de AE SCE CK cure othe sys tene Software for the multiprocessor system can relatively easily be written in the form of a number of independent co operating possibly cyclic processes These processes can be executed simultaneously Communication and synchronisation between processes can be achieved in different ways namely by using semaphores with operations WAIT and SIGNAL by using buffers with operations SEND and RECEIVE by using global variables The number of processes present in the system shouldn t be limited to the number of available processors This implies that it must be possible for a processor to serve more processes processor sharing 10 We can distinguish three states in which a process can be in relation to the processors T
39. mitations of the system are mentioned and suggestions for extensions are made Some communication and synchronisation routines are added to Pascal The so created language is called Pascal plus PAP and is described in appendix B Appendix A gives a description of the funetion of the preprocessor which transforms a program written in Pascal plus into Pascal Appendices C and F give implementation details of some parts of the system whilst appendix E gives a description of the software Appendix D describes the structure of the local memory Some software modifications needed in case of hardware changes are described in appendix G During the development of the system some bugs in the Pascal compiler were detected These are reported in appendix H A program already written earlier was used as test and demonstration program Some modifications were made in this program These are described in appendix I Introduction Within the research project ER 17 a multiprocessor system has been realized which consists of two LSI 11 23 processors which operate on a common memory Objective of the thesis project is to realize the possibility to execute simultaneous processes written in Pascal on this hardware configuration For the interaction between these processes one wants to have communication and synchronisation primitives at one s disposal Starting the processes must also be implemented It is assumed that the reader is familiar
40. ns none Suggestions for extensions none Further ermarks see under SEND E 37 Description of the procedure RESPS Heading PROCEDURE RESPS PS INTEGER Task of the procedure restoring the processor status with the contents of variable PS Parameter description PS contains the processor status the calling process should get Called procedures and functions none Calling procedures and functions BSARPS Suggestions for extensions Perhaps the variable PS should be cleared after restoring the processor status Further remarks none E38 Description of the procedure RETTOM Heading PROCEDURE RETTOM VAR INQUEUE QUEUE VAR R5 INTEGER Task of the procedure place the calling process in INQUEUE return to the program part that the calling process started This happens with help of the contents of R5 Parameter description INQUEUE the queue in which the calling process is placed R5 contents of register 5 of the program part that started the calling process Called procedures and functions QENTER Calling procedures and functions INIT Suggestions for extensions none Further remarks none E 39 Description of the procedure SAVPS Heading PROCEDURE SAVPS VAR PS INTEGER Task of the procedure saving the processor status in variable PS Parameter description PS contains after procedure execution the processor status of the calling process Called procedures and functions
41. o the buffer BUF which is a process parameter The messages are preceded and followed by a carriage return Parameter description BUF A buffer where all characters are send to The buffer should have messages of one element of type ASCII or BYTE Called procedures and functions RECEIVE SEND Suggestions for extensions none Further remarks It is recommanded to start the process with a high priority Also the buffer which is given as parameter can be coupled to a TTUIT process directly Estimated hardware stacksize required is 15 words Estimated software stacksize required is 70 words The process is not CPU bound Appendix F Description of the compiler modification In contrary with the design considerations mentioned in chapter 2 1 one compiler modification was made This was necessary because otherwise it was impossible to report the linenumber where an error occured see chapter 4 2 The modification made stores the linenumber at an address in local memory now 772B instead of 2 R3 The modification only concerns the compiler procedure LINENODEF In this procedure the lines GEN2 MOV AUTINC PC INDEX GP GENCONST LINENO GENCONST LINEADDR l which generate the instruction MOV lineno 2 R3 are changed to GEN2 MOV AUTINC PC AUTINCDEF PC GENC ONST LINENO GENCONST 772B which generates the instruction MOV lineno 772 G l Appendix G Software changes needed for hardware chang
42. ocedure Generate an error message Parameter description NR the number of the error to be generated KIND defines the seriousness of the error 1 fatak 2 warning 4 message Called procedures and functions WRERROR Calling procedures and functions STRINGTOINTEGER INTEGERTOSTRING Suggestions for extensions none Further remarks The procedure can be used in RSX programs too E 43 Description of the procedure SPSABW Heading PROCEDURE SPSABW VAR SLOT WORD VAR PS INTEGER Task of the procedure saving the processor status in variable PS and executing a busy wait on the variable slot Parameter description SLOT word which controls access to a queue PS contains the processor status of the calling process after execution of the procedure Called procedures and functions SAVPS BWAIT Calling procedures and functions SIGNAL QLEAVE BYE WAIT QENTER Suggestions for extensions none Further remarks The processor status is on absolute address 777 776B which corresponds with virtual address 177 776B SPSABW means Save Processor Status And Busy Wait Description of the procedure STRINGTOINTEGER Heading PROCEDURE STRINGTOINTEGER STRING S VAR I INTEGER Task of the procedure Converting an array of CHAR or part of it to an integer Parameter description S array or array part to be converted I conversion result Called procedures and functions PARAMERROR SIMPLEERROR Calling
43. ocesses 2 4 Addressing in Pascal 2 5 Choice of an alternative Implementation 3 1 Implementation of the local stacks 3 2 Implementation of the process descriptor 3 3 Implementation of the queues 3 4 Addressing the I O page 3 5 Addressing the loeal memory Error handling 4 1 Detecting an error 4 2 Generating an error message Limitations Conclusions References Appendix A Appendix B Appendix G Appendix D Appendix E Appendix F Appendix G Appendix H Appendix I and suggestions for extensions of the system Description of the function of the preprocessor Pascal plus user manual Generating a device common Structure of the local memory Software description Description of the compiler modification Software changes needed for hardware changes Some remarks on Pascal Modifications made in the practicumsys teem Oo o ODD On amp F W ND PRP PPP RPP ee PP IYI WAHANUHR RR WE O RBS Preface This report describes a system which can execute parallel processes written in Pascal on a multiprocessor system First chapter 1 a description of the existing hard and software is given In the second chapter the general structure of the system is described Chapter 3 deals with the implementation of the system Emphasis is laid on the special problems caused by the hardware configuration used Chapter 4 explains the error handling of the system whilst in chapter 5 the li
44. otected Also the operations MARK and RELEASE must be forbidden because all processes have a common heap All the other alternatives offer no good solution for this problem either 14 3 Implementation All process stacks are created in the software staek This happens by claiming an amount of space from top of stack downward The main program shall do this first and so create a main program stack Processes reserve their stack space when they are started The user must indicate how much space must be reserved For the main program this is a fixed amount because the main program is not started by a user unlike processes A process which is started shall first adjust its hardware and software stackpointer R6 resp R5 so that they point to the claimed space on the software stack The distribution of this space between hardware and software stack must be indicated by the user when starting dnek Imp ementa tion or the process descr t Pion Every process has a process descriptor which contains several essential data of the process namely The software stackpointer R5 if a process is not running when a process becomes running all registers are restored via this stackpointer A pointer to the processor queue which contains the process when it is runnable The processor status if a process is or may become not running A sequence number that identifies the process These succesive numbers are assigned by the syst
45. p by NEW E 12 Description of the procedure ATTMAC Heading PROCEDURE ATTIMAC DEV ADDRESS VAR SEM SEMAF BLOK ATTBLK Task of the procedure Generating an interrupt service routine Parameter description DEV address of the interrupt vector SEM the semaphore to be attached to an interrupt BLOK beginaddress of the interruptroutine Called procedures an functions SIGNAL in the interrupt service routine Calling procedures and functions ATTACH Suggestions for extensions none Further remarks The interrupt service routine signals the given semaphore Interrupt service routines run on processor priority 7 E 33 Description of the procedure BSARPS Heading PROCEDURE BSARPS VAR SLOT WORD PS INTEGER Task of the procedure executing a busy signal on the variable slot and restoring the processor status Prameter description SEOT word which controls access to a queue PS contains the processor status the calling process should get Called procedures and functions BSIGNL RESPS Calling procedures and functions SIGNAL QLEAVE CHANGE WAIT QENTER Suggestions for extensions none Further remarks BSARPS means Busy Signal And Restore Processor Status E 14 Description of the procedure BSIGNL Heading PROCEDURE BSIGNL VAR SLOT WORD Task of the procedure Move a 1 to SLOT in an indivisible operation Parameter description SLOT the variable to be filled with al Called pro
46. pointer to the first process descriptor of the queue in which the calling process must be placed Called procedures and functions QIN BSARPS WAKEUP Calling procedures and functions WAIT BYE Suggestions for extensions none Further remarks none E 17 Description of the procedure CHREG Heading PROCEDURE CHREG TEMPPDPT PDPT HSBEG INTEGER SSBEG INTEGER VAR R5 INTEGER Task of the procedure saving of R4 R5 R6 the processor status the pdpointer and the linenumber on the software stack saving register 5 in variable R5 initializing of R5 and R R5 SSBEG R6 HSBEG initializing the just created new stack 7 words on the software stack 2 words on the hardware stack Parameter description TEMPPDPT address of the process descriptor of the process to be started HSBEG initial value of the hardware stackpointer SSBEG initial value of the software stackpointer R5 variable for saving R5 of the caller Called procedures and functions none Calling procedures and functions NEWSTK Suggestions for extensions check if stacks aren t made too small if a minimal size is required Further remarks none E 18 Description of the procedure COPYFROM Heading PROCEDURE COPYFROM VAR FROM CHAR VAR TOT CHAR OFFSET INTEGER NROFBY TES INTEGER Task of the procedure Copying nrofbytes bytes from address from offset to the address tot Parameter description FROM address that when of
47. procedures and functions none Suggestions for extensions none Furhter remarks ae Blanks in the string are ignored If an illegal character is detected no blank sign or digit an error message 94 is generated The ascii value of the character is given in this message As conversion result a zero is given If overflow is detected MAXINT or MININT depends on the sign already detected is given as conversion result and an error message 95 is generated E 45 Description of the procedure WAIT Heading PROCEDURE WAIT VAR PDPOINTER PDPT VAR SEM SEMAF Task of the procedure placing the calling process in a queue if the semaphore counter is zero otherwise decrement the semaphore counter and continue Parameter description PDPOINTER pointer to the proeess descriptor of the calling process SEM the semaphore on which must be waited Called procedures and functions SPSABW l BSARPS CHANGE Calling procedures and functions SEND RECEIVE Suggestions for extensions none Further remarks none E 46 Description of the procedure WAKEUP Heading PROCEDURE WAKEUP VAR Q QUEUE VAR PDPOINTER PDPT Task of the procedure wake a process If possible a process from Q is awoken otherwise a process from the READYQ This is tried until a process is awake Parameter description Q queue from which a process is going to be awoken if not empty PDPOINTER pointer to the process descriptor of the process which i
48. receded by the special symbol UNIV Use of this feature is not recommanded for normal use Procedure and function declarations can be preceded by the special symbol SYSTEM This provides a possibility to identify the calling process Its implementation and consequences are not discussed here How to use Pascal plus A file written in Pascal plus can be transformed into a taskfile in the following way First transform the program source to a Pascal source This can be done by the preprocessor which can be activated with PAP lt passource gt lt list gt lt papsource gt If no file designators are given the preprocessor will prompt with PAP gt and then the user can give the file specifications Default extensions are PAS LST and PAP respectively Default device is SY and default uic is the uic under which PAP is run The passource and listfiles may be omitted If no error occurs the passource file can be compiled with the Ericsson Pascal compiler See for a detailed description of it the User Manual Taskbuilding the file is also conform the description in the Ericsson Pascal User Manual A user must however enter the options STACK 4000 7 and COMMON IONEW RW Furthermore the option EXTTSK must be given a value greater than the total stackspace used by all processes the main program takes 330 words stackspace plus all global declared variables plus all variables created with NEW during program execution Th
49. ring the linenumber This is now stored in the local memory IEBW means Initialize ErrorBuffer Word Description of the procedure INIT Heading PROCEDURE INIT VAR PDPOINTER PDP Task of the procedure Placing the calling process in its processor queue Returning to the program part that started the calling process Parameter description PDPOINTER pointer to the process descriptor of the calling process Called procedures and functions RETTOM OVFLCHK Calling procedures and functions a just started process Suggestions for extensions none Further remarks none Description of the procedure INITIALIZE Heading PROCEDURE INITIALIZE Task of the procedure Initialization of the processor queue s byequeue readyqueue number startreg newreg and errorbuf Placing the address of errorbuf on 2 R3 Parameter description none Called procedures and functions IEBW Galling procedures and functions main program when started Suggestions for extensions none Further remarks en none E 23 Description of the function INITTOS Heading FUNCTION INITTOS INTEGER Task of the function Displaying the value of R5 in the function result Parameter description INITTOS contains after execution the value of R5 Called procedures and functions none Calling procedures and functions none Suggestions for extensions none Further remarks Punction call is added by PAP to initialize t
50. ror message is generated Overflow of the hardware or software stack can occur at any moment Beeause testing on overflow after each statement execution gives a lot of overhead it is implemented as follows analogous to Ericsson Pascal At procedure entry is tested if a ceftain amount of space is available on both stacks and if not an error message is generated The minimal required stack space is 40 words on the software stack and 10 words on the hardware stack This is completely conform Ericsson Pascal The last three errors can only occur in the procedures mentioned and are detected there 4 2 Generating an error message Normally the error messages generated by Pascal are handed over to RSX which prints them This is impossible in our system because we don t have RSX at our disposal Therefore all error messages are send to the standard buffer ERRORBUF There is also a standard process ERRORLOG available which converts messages from ERRORBUF to characters which 18 thereafter can be printed by the standard process TTUIT see for a descrip tion of the standard processes appendix E A problem that arises when generating error messages concerns the line numbers In the error message the number of the line in which the error occurs is given This linenumber is stored in one of the hidden variables see paragraph 2 4 If on our multiprocessor system more processes are executed simultaneously this hidden variabl
51. rrays are always packed so contain 2 characters per word one should be careful when comparing arrays of odd length Comparison of the elements is done on word basis so comparing identical arrays of odd length can yield the value FALSE because the last unseen byte of both arrays differs It is impossible to get a listfile when switches are placed after the object file If a variable is declared in the procedure heading as S ARRAY INTEGER OF CHAR one cannot use the statement WRITE TTY S in that procedure One cannot use the file TTY in separate compiled procedures unless it is included in the procedure heading and therefore must be included at every procedure call It was impossible to create a working memory resident overlaid compiler All the compilers that were build memory resident trapped when used The H switch doesn t operate as was expected Occurences of the H switch after the first BEGIN of the main program have no influence at all When starting a program the dynamic option switch word hidden variable 4 R3 is initialized according to the last occurrence of the H switch before the first BEGIN of the main program even if this last occurrence was in a procedure declaration During program execution the dynamic option switch word is never changed Message 41 and the corresponding IORESULT are not generated if number 32768 is entered Entering too negative numbers results in reading number 77777B instead of M
52. s awoken Called procedures and functiens QLEAVE Calling procedures and functions PHOENIX CHANGE Suggestions for extensions none Further remarks none E 47 Description of the procedure WRITEREG Heading PROCEDURE WRITEREG PART INTEGER REG ADDRESS CONT WORD Task of the procedure writing on a virtual memory address Parameter description PART tells in which part of 4k words we want to write PART 0 between O and 4k ete REG gives an address inside these 4k words 13 bit CONT the word which must be written to the address Called procedures and functions none Calling procedures and functions none Suggestions for extensions A better way to transport the address Further remarks see under READREG B 48 Description of the routine WRERROR Heading none Task of the routine sending an error message to ERRORBUF if needed determined by the dynamic option switch word 4 R3 If a fatal error occurs and a user doesn t want to continue after a fatal error a BYE is executed Parameter description see listing Called procedures and functions SEND BYE Calling procedures and functions NEWCHK OVFLCHK PARAMERROR SIMPLEERROR all Pascal runtime routines that generate error messages Suggestions for extensions none Furhter remarks Errorbuf address is in 2 R3 The format of an error message can be found under the type descriptions The routine is based on the pascal runtim
53. se are described below All assembler procedures are replaced by calls of READREG or WRITEREG Starting the processes is implemented The types MESSAGE and MSGBUF are used Some calls of SEND and RECEIVE are changed to transmit integers instead of character arrays The process REKENPROCES is rewritten This is done because the ADC gives 12 bit samples instead of 8 bit ones The processes TEXTITOCHAR and TEXT2TOCHAR TTYLTOCHAR and TTY2TOCHAR TTYLFROMCHAR and TTY2FROMCHAR are replaced by processes TEXTTOCHAR TTYTOCHAR and TTYFROMCHAR These processes are started twice with shared code The standard procedures STRINGTOINTEGER and INTEGERTOSTRING are used
54. used by the overhead and inefficiency of Pascal Speed can be increased by writing the system procedures in assembler or microcode instead of Pascal Processes which have executed a BYE see appendix E can never be restarted This can easily be changed but then it is necessary that processes can be identified by their names for instance this name can be placed in the process descriptor Also a new procedure has to be created to allow processes to leave the system without restart possibility This can be used to exit from noneyelie processes The execution speed of user processes can be enlarged by adding more arbiters and processors A description of the system changes caused by hardware changes is given in appendix G Conclusions The system developed is in quite good agreement with the design considerations mentioned in paragraph 2 1 On some points however some tedious limitations exist These limit the usability of the system The system is rather flexible modular and easy to maintain A disadvantage is its dependence on Ericsson Pascal especially on the stack structure the addressing mechanism and the property of the compiler not to save the registers upon external procedure entry Also when wanting to use another compiler the source must be available in order that the compiler modification can be made References l 2 3e Le K Jensen N Wirth Pascal User Manual amp Report Springer Verlag 19
55. xist Processes are separate programs which communicate through a kind of external variables There is only one program in which all processes are known as procedure or through a newly introduced PROCESS statement For a good consideration of the benefits and disadvantages of a choice between these alternatives it is necessary to know how the addressing and allocation of variables in Pascal is arranged ll Pads Addressing in Pesce In Pascal it is only possible to introduce new variables at the beginning of the description of the main program or a procedure This in contrast with for instance ALGOL where this is possible at every block entry In Ericsson Pascal all variables are placed on a stack This stack is also used to store temporary results The structure of the stack can be seen in fig 2 R3 points to the begin of the software stack this stack grows downward R4 points to the place where the data of the last entered procedure begin and R5 points to the top of the software stack Ericsson Pascal has also some so called hidden variables These are placed just above the software stack and are used by the runtime system for administration Only a few of these hidden variables are interesting for us namely 2 R3 which contains the linenumber of the line being executed 4 R3 which contains the dynamic option switch word that controls the error handling 8 R3 which points to the top of the heap
56. ypes and variables are described Also a description of the procedures functions and system processes is given These are however not described at statement level Readers interested in all fine implementation details are referred to the listings and the comments inserted there E 3 New types The following types are added to Pascal to create PAP or as hulptypes for the implementation of the system PDPT PRODESC defines a pointer to the type PRODESC QPOINTER QUEUE defines a pointer to the type QUEUE PRODESC RECORD SP WORD PROCXQ QPOINTER PS INTEGER NR INTEGER PRI INTEGER HST INTEGER SST INTEGER NEXT PDPT END defines a process descriptor A process descriptor contains some vital information of a process The fields have the following meaning SP contains the software stackpointer R5 of a sleeping process PROCXQ pointer to the queue in which a process resides when it is runnable PS contains the processor status of a sleeping process NR contains a sequence number assigned when a process is started The first started process has NR 0 HST contains the limit which may not be exceeded by the hardware stackpointer R6 when a procedure is entered SST contains the limit which may not be exceeded by the software stackpointer R5 when a procedure is entered NEXT pointer to another process descriptor This field is among others used to implement queues E 4 WORD
57. ystem is chosen as development system During execution of programs on the multiprocessor system we can t use RSX executives like QIO because RSX like all standard PDP 11 operating systems gives no multiprocessor support Therefore all Pascal system routines that make requests to RSX must be prohibited or modified This applies especially to runtime error messages because they perform I O autonomously i e without a standard procedure being called in the user program There is a preprocessor available written by W J M Lemmens described in a THE report to be published This preprocessor should be used before the Pascal compilation Its task is among others the addition of the declarations of the communication and synchronisation routines and Mem bus LSI bus control li ontro ines COMM COMM Fig 1 Multiprocessor system some new standard types e g semaphore A more comprehensive deseription of the function of the preprocessor can be found in appendix A 2 Problem analysis and structure of the system 2 l Design considerations The following considerations served as starting points during the develop ment of the software As much as possible the Pascal compiler is left unaffected because changing the compiler is a rather complicated task This also avoids the arising of two incompatible compilers and all problems involved with it duplicate libraries and so on The Pascal syste
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