Error in thumb_crt0.s ?

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Juraj Vanco

• August 30, 2009 07:39

Hello,

I experienced problem with stack variables, that were overlaying with bss segment: anyway, in Symbol Browser, everything was ok (segments were not overlayed). So I was debugging from startup and found this:

_start:

#ifdef __RAM_BUILD

  ldr r0, =__stack_end__

  mov sp, r0

#endif

So the SP register was set only in RAM build. When I uncomented it, everything was ok (variables in stack were allocated really to the stack segment). Is that an error?

CrossStudio for ARM 1.7, build 22.

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  Jon Elliott

  • August 31, 2009 16:45

  This isn't an error, in the FLASH build the stack is set up when the processor resets by loading the contents at address 0 into the SP.

  Where you may have a problem is if you've re-located the start of FLASH away from address 0 in which case the stack won't be set up.

  Having said that, I believe the latest version of thumb_crt0.s always sets up SP to avoid users falling over this very problem.

  Regards,

  Jon Elliott

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  Juraj Vanco

  • August 31, 2009 17:53

  Thanks for reply.

  I use Rowley's STMicroelectronics STM32F10x CPU Support Package v1.11. Linker places .text section at 0x08000000, so it is not 0x00000000 and that's probably why SP register is not correctly loaded. How to force the linker to place code at address 0x00000000?

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  Jon Elliott

  • August 31, 2009 18:51

  Looking at the release notes, the thumb_crt0.s file was modified to allow SP to be setup correctly when a FLASH application is located away from 0x00000000 at version 2.0.2 of CrossWorks so make sure you're using this version or later.

  The memory map and section placement files are used to place sections in memory, however using the latest version of thumb_crt0.s is the correct fix for this problem, not moving sections around in memory.

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  Juraj Vanco

  • August 31, 2009 19:30

  Thanks a lot, solved now. I am using commercial CW 1.7.22.

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