AVR-GCC - Pumpkin, Inc.
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1. P REALTIME SOFTWARE REAL TIME SOFTWARE Refe rence Manual 750 Naples Street San Francisco CA 94112 415 584 6360 htto www pumpkininc com Salvo Compiler Reference Manual AVR GCC J Salvo The RTOS that runs in tiny places Copyright 2003 Pumpkin Inc last updated on Jun 5 2008 All trademarks mentioned herein are properties of their respective companies The RTOS that runs in tiny places Introduction Reference Manual This manual is intended for Salvo users who are targeting Atmel http www atmel com AVR and MegaAVR microcontrollers with GNU s AVR GCC C C compiler for AVR Note It is assumed that the IDE used is Atmel s AVR Studio commonly installed as part of the WinAVR tool suite Related Documents Example Projects Features The following Salvo documents should be used in conjunction with this manual when building Salvo applications with the AVR GCC C C compiler e Salvo User Manual Example Salvo projects for use with the AVR GCC C C compiler can be found in the Pumpkin Salvo Example AVR directories of every Salvo for Atmel AVR and MegaAVR distribution Tip These example projects can be easily modified for any AVR or MegaAVR device Table 1 illustrates important features of Salvo s port to the AVR GCC C C compiler Available directly from Atmel s website http www atmel com 2 Windows for AVR available at http wi2. Reference Manual Type Target Option eae a a Salvo aay configuration type multitasking with delays and events f freeware multitasking with delays l standard multitasking with events multitasking only Bee lige multitasking with delays and events P tasks can wait with timeo target option avr AVR and MegaAVR no option goan 128KB and smaller i library includes debugging information program memory atm256 MegaAVR with 256KB and larger program memory Figure 1 Salvo library nomenclature GNU s AVR GCC C C C compiler Salvo Lite distributions contain freeware libraries All other Salvo distributions contain standard libraries See the Libraries chapter of the Salvo User Manual for more information on library types Each library is intended for one or more specific processors with internal SRAM Table 1 lists the correct library for each AVR and MegaAVR processor Target Code Processor s AVR and megaAVR devices with up to 128KB of program memory avr e g AT90S8515 ATmega16 ATmegai28 These libraries all use the basic AVR instruction set megaAVR devices with 256KB or more of program memory atm256 e g ATmega2561 These libraries use the extended AVR instruction set Table 1 Processors for Salvo libraries GNU s AVR GCC C C compiler Salvo Pro users can select between two sets of libraries standard libraries and standard libraries incorporating source level debugg
3. CC C C compiler Note Salvo Lite libraries have precompiled limits for the number of supported tasks events etc Salvo LE and Pro libraries have no such limits See the Libraries chapter of the Salvo User Manual for more information There are a total of 22 Salvo libraries for the AVR GCC C C compiler Each Salvo for Atmel AVR and MegaAVR distribution contains the Salvo libraries of the lesser distributions beneath it B salvo Reference Manual Target Specific Salvo Source Files The source file salvoportgccavr s is needed for Salvo Pro source code builds for targets with up to 128KB program memory space The source file salvoportgcecavr256 S is needed for Salvo Pro source code builds for targets with 256KB and greater program memory space Note Never re name portgccavrXxx S tO portgccavrXXxX s as the makefile treats these as two different files The s file is a user ASM code whereas the s file is an intermediate file generated by AVR GCC that can be deleted salvocfg h Examples Below are examples of salvocfg h project configuration files for different Salvo for Atmel AVR and MegaAVR distributions Salvo Lite Library Build include lt avr io h gt define OSUSE LIBRARY TRUE define OSLIBRARY_TYPE OSF define OSLIBRARY CONFIG OST define OSTASKS 2 define OSEVENTS 4 define OSEVENT_FLAGS 0 define OSMESSAGE QUEUES 1 Listing 1 Example salvocf
4. VR community and is the author of various AVR centric material to be found at the popular AVR Freaks http www avrfreaks net website tinyAVR devices are not supported because of their lack of RAM This is done automatically through the __GNUC__ and __AVR symbols defined by the compiler The Salvo libraries provided with Salvo Lite and LE do not contain AVR GCC debugger compatible debugging information because this requires the inclusion of source file listings K Salvo 4 1 2 with WinAVR release 20071221rc1 text data bootloader sections in bytes with optimization setting of 00 data bss noinit sections in bytes with optimization setting of O0 7 This hook is valid for all AVR and MegaAVR targets because the register and GIE bit locations are the same for all targets This hook is valid for all AVR and MegaAVR targets because the watchdog control register is the same for all targets Salvo Pro application can reduce this by 2 bytes one return address by inlining OSSched E g task control blocks queue pointers counters etc N RM GCCAVR Salvo Compiler Reference Manual AVR GCC 11
5. akefile with the rest of the linker flags normally called LFLAGS and in fact your makefile may already be set up for working with external SRAM If you do this you also have to make sure the processor hardware is set up to use external RAM It is best to do this as early as possible in fact the absolute best way is to make a file called xram S and fill it with something like this begin xram S include lt avr io h gt section initl ax progbits ldi r16 1 lt lt SRE 1 lt lt SRW out _SFR_IO_ADDR MCUCR r16 7 end xram s This would work for the AT90S8515 enabling the external XRAM with one wait state The file should be added to your project Note RM GCCAVR Salvo Compiler Reference Manual AVR GCC The RTOS that runs in tiny places Reference Manual Data Segments that the code executed in that file takes place very early on before anything like the stack has been set up The RAMPD register is normally used to access the entire data space on processors with more than 64K bytes data space There are no provisions for accessing Salvo s global objects outside of the current data segment of 64K bytes Credits amp Acknowledgements Colin O Flynn originally wrote the Salvo context switcher in salvoportgccavr sS created the Salvo project makefile system for the Salvo v3 port to AVR GCC and wrote much of the documentation surrounding the Salvo v3 port to GNU s AVR GCC compiler Colin is active in the A
6. g h for library build using libsalvofgccavr t a Salvo LE amp Pro Library Build include lt avr io h gt define OSUSE_ LIBRARY TRUE define OSLIBRARY_TYPE OSL define OSLIBRARY_ CONFIG OST define OSTASKS 7 define OSEVENTS 13 define OSEVENT_FLAGS 3 define OSMESSAGE QUEUES 2 Listing 2 Example salvocfg h for library build using libsalvolgccavr t a 6 RM GCCAVR Salvo Compiler Reference Manual AVR GCC Salvo Pro Source Code Build include lt avr io h gt define OSENABLE IDLING _HOOK RUE define OSENABLE SEMAPHORES TRUE define OSTASKS 9 define OSEVENTS 17 define OSEVENT_FLAGS 2 define OSMESSAGE QUEUES 4 Listing 3 Example salvocfg h for source code build Performance Memory Usage tutorial memory usage total ROM total RAM AVR AT90S8515 tut5lite 2472 58 AVR AT90S8515 tut5le 2448 58 AVR AT90S8515 tut5pro 3610 57 Table 3 ROM and RAM requirements for Salvo applications built with GNU s AVR GCC C C compiler User Hooks Overriding Default Hooks In library builds users can define new hook functions in their projects and the linker will choose the user function s over the default function s contained in the Salvo library In source code builds users can remove the default hook file s from the project and substitute their own
7. he 256KB or greater program memory space Salvo supports these parts by considering only the low order 16 bits of each task function pointer tFP Therefore Salvo tasks can only be located in the lower 128KB of program memory space When building a Salvo application for 256KB or greater program memory space from Salvo libraries or Salvo source code be sure The RTOS that runs in tiny places Stack Issues External SRAM 10 Reference Manual to use the library or source code modules appropriate for the larger program memory model The AVR GCC compiler uses the same stack for return addresses and for local storage The y pointer R29 R28 is used as a frame pointer Compared to a non Salvo non multitasking application with similar call trees the corresponding Salvo application will require an additional 4 bytes i e one return addresses in the hardware stack Salvo s global objects can be placed in internal or external RAM The placement of data objects is controlled by linker options and takes the format w1 Tdata 0x800000 start for relocationg the program data section ie variable storage where the 0x800000 start means hex address with an 0x800000 offset There is no end location it is your responsibility as a programmer to not use more RAM than you have For example AVR GCC W1 Tdata 0x800260 specifies that the data program area start at 0x260 the end of internal SRAM This could be added to your m
8. hook functions Idling The default idling hook in salvohook_idle c is a dummy function as shown below void OSIdlingHook void Listing 4 Default Salvo idling hook for GNU s AVR GCC C C compiler RM GCCAVR Salvo Compiler Reference Manual AVR GCC 7 The RTOS that runs in tiny places Interrupt Watchdog Reference Manual Users can replace it e g with a directive to put the AVR to sleep by building their own version with their application The default interrupt hooks in salvohook_interrupt c are 7 shown below static uint8_t sreg void OSDisableHook void uint8_t sreg_local sreg_local SREG cli sreg sreg_local void OSEnableHook void SREG sreg Listing 5 Default Salvo interrupt hooks GNU s AVR GCC C C compiler These functions clear the GIE bit i e disable global interrupts across Salvo s critical section and restore the bit to its previous value thereafter These hooks are suitable for all applications These hooks work very well within Salvo services called from interrupts as the GIE bit is automatically cleared upon entry to an interrupt Therefore interrupts are not re enabled at the end of a Salvo service that is called in an ISR This avoids unnecessary interrupt nesting The use of the auto variable sreg_local avoids issues that would affect the shared global sreg when a Salvo service is called from within an ISR Note Not disabling all s
9. ing information The latter have been built with the AVR GCC C C compiler s g command line option This adds source level debugging information to the libraries making them RM GCCAVR Salvo Compiler Reference Manual AVR GCC The RTOS that runs in tiny places Configuration Build Settings Available Libraries RM GCCAVR Salvo Compiler Reference Manual AVR GCC Reference Manual ideal for source level debugging and stepping in the AVRStudio IDE To use these libraries simply select one that includes the debugging information e g libsalvolgcecavrit a instead of one without e g Libsalvolgccavr t a in your project Different library configurations are provided for different Salvo distributions and to enable the user to minimize the Salvo kernel s footprint See the Libraries chapter of the Sa vo User Manual for more information on library configurations Salvo s libraries for the AVR GCC C C compiler are built using the default settings outlined in the Libraries chapter of the Salvo User Manual Target specific settings and overrides are listed in Table 2 Target specific Settings Delay sizes 8 bits dummy can be overridden disables then restores GIE bit can be overridden Watchdog hook clears WDT without other changes can be overridden System tick counter available 32 bits Task priorities enabled Idling hook Interrupt hook Table 2 Build settings and overrides for Salvo libraries for GNU s AVR G
10. navr sourceforge net RM GCCAVR Salvo Compiler Reference Manual AVR GCC Reig that runs in tiny places Refe re nce Ma n u al General Abbreviated as GCCAVR Salvo Lite LE amp Pro for Atmel AVR and MegaAVR Supported targets entire AVR and MegaAVR family Header file s salvoportgccavr h Available distributions salvoportgccavr s salvoportgccavr256 S salvocfg h Compiler auto detected yes Include target specific header file in salvocfg h Other target specific file s 2 yes Libraries Located in Lib GCCAVR Context Switching function based via Method OSDispatch amp OSCtxSw Labels required no Size of auto variables and function total size must not exceed 254 8 bit parameters in tasks bytes Memory amp Registers Internal and external RAM yes yes see section on external supported memory Interrupts Interrupt latency in context switcher eee Interrupts in critical sections wa ae controlled via Default behavior in critical sections see example user hooks Debugging Source level debugging with Pro library builds yas Compiler Bitfield packing support no printf p support yes yes va_arg support yes Table 1 Features of Salvo port to GNU s AVR GCC C C compiler Libraries Nomenclature The Salvo libraries for the AVR GCC C C compiler follow the naming convention shown in Figure 1 RM GCCAVR Salvo Compiler Reference Manual AVR GCC 3 The RTOS that runs in tiny places
11. ource of interrupts that call Salvo services during critical sections will cause the Salvo application to fail The default watchdog hook in salvohook_wdt c is shown below void OSClrWDTHook void RM GCCAVR Salvo Compiler Reference Manual AVR GCC The RTOS that runs in tiny places Compiler Issues Reference Manual wdt_reset Listing 6 Default Salvo watchdog hook for GNU s AVR GCC C C compiler Users can replace it e g with a dummy function this would stop Salvo from clearing the watchdog timer and allow the user to clear it elsewhere by building their own version with their application Incompatible Optimizations Register R1 All compiler optimizations 01 02 amp 03 are currently incompatible with Salvo code and Salvo tasks Users should build their projects with optimizations off 00 Other code e g user functions non Salvo libraries etc can be used with compiler optimizations without issues A solution to allow compiler optimizations to be used with Salvo code and Salvo tasks is currently under development The avr libc library which is an integral part of AVR GCC assumes register R1 will always have a 0 value and Salvo does not modify this register Special Considerations ATmega2560 2561 256KB and greater program memory RM GCCAVR Salvo Compiler Reference Manual AVR GCC GNU s AVR GCC C C compiler does not yet fully support function pointers that span t
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