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How to store the current program counter in a C variable

Al2966
Intellectual 355 points

Hi

I need to store the current program counter in a C variable.

 

Any code examples?

Thanks,

  • 0
    TI__Mastermind 24460 points

    I don't think we have any codes that do this specifically, but you could trigger an incidental interrupt, then when in the ISR store the PC (the contents of which have been pushed on the stack) in a variable, then return. See figure 2-7 of the 1xx User's Guide

  • 0 in reply to Brandon08
    Intellectual 355 points

    Yes this is what I would like to do.

    I would like to be able to get the SP value into a C variable and then I would manage to recover the PC using pointers. I am just not familiar with assembly,

     

    int StackPointerVar;

    StackPointerVar = ???

     

    Any suggestions?

    Thanks,

  • 0 in reply to Al2966
    Prodigy 140 points

     

    Before serving an ISR, the PC + SR are automatically pushed on the stack. If you use a compiler like IAR, it also automatically pushes R4 to R11.

    The way the PC is saved on the stack depends wether the MSP430 has 16 or 20 bits register:

    •  In the case of 16 bits PC,  you can get the value of it by using:

     unsigned short savedPC = (unsigned short *) (__get_SP_register() + 9);  //Stack grows towards lower addresses...

    • In the case of 20 bits PC (MSP430X has memory addressable above 64K):

     unsigned long savedPC = (unsigned short *) (__get_SP_register() + 9)  + ((((unsigned short *) (__get_SP_register() + 8)) & 0xF000) << 4);

     

    This is not tested so there may be conceptual or code errors:)

  • 0 in reply to cyberstorm
    Intellectual 355 points

    Thanks Cyberstorm,

    That exactly what I was looking for. ;)

    I dont really get the + 9 and + 8 though.

    Since just got into interrupt I expect the

    (SP) to be pointing to Previous SR

    (SP + 2) to be pointing to the previous PC

    Am I missing something?

  • 0 in reply to Al2966
    Prodigy 140 points

    Hi Al,

    I added the +8 because the compiler also stores 8 registers(R4 to R11) on the stack, but you may check if this applies also for your compiler.

    Program Counter in case of MSP430X is splitted on two registers, hence the +8 and +9.

     

  • 0 in reply to cyberstorm
    Intellectual 355 points

    OK,

    I got it working with the following code in CCE with f5438 with +24 and +26 offsets.

     

    Thanks again

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