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Cortex M3 - how the startup works

Sebastian Gaertner
Note: This was originally posted on 15th May 2009 at http://forums.arm.com

Hi all,

I have some problems understanding the startup procedure of the ARM, here Cortex M3.
Address 0x0000.0000 holds the MSP (main Stack Pointer) and it is the 1st register the Cortex will read after a reset/start.

Address 0x0000.0004 holds the Reset Vector and it will be read after reading the MSP before. Then it jumps to the address that is placed in this register. The rest of the program is then called.

Now the question is: when do I write the values to the both registers at address 0x0 and 0x4?

E.g. if I have my bootcode at address at flash address 0x100 I need to write the value into the register 0x4. But when I power on the device it just will read from 0x4 before I can write to there.
Parents
  • Note: This was originally posted on 1st June 2009 at http://forums.arm.com

    with this I get the following error after linking the files:
    Error: L6967E: Entry point (0x00000000) points to a THUMB instruction but is not a valid THUMB code pointer.
    I googled for this problem but could not get a answer that fits.
    Does anybody have an idea why the 0x0 is not a THUMB pointer?


    A pointer to a thumb routine should have bit0 set. However, main (or any other function for that matter) will always be placed at a location which is a multiple of four. So the proper pointer to a thumb main would be (main + 1).
Reply
  • Note: This was originally posted on 1st June 2009 at http://forums.arm.com

    with this I get the following error after linking the files:
    Error: L6967E: Entry point (0x00000000) points to a THUMB instruction but is not a valid THUMB code pointer.
    I googled for this problem but could not get a answer that fits.
    Does anybody have an idea why the 0x0 is not a THUMB pointer?


    A pointer to a thumb routine should have bit0 set. However, main (or any other function for that matter) will always be placed at a location which is a multiple of four. So the proper pointer to a thumb main would be (main + 1).
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