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TMS320F28335: How to include function pointer at a specified flash location

Christopher Mounce
Prodigy 160 points
Part Number: TMS320F28335


I'm trying to add a function pointer at a specified location in flash. I've tried the following code, but I'm getting nothing written to the specified location in flash; it's just empty (all Fs). I've tried the CODE_SECTION option, but that just places the entire function in that memory space, I just need the pointer there.

In main.c:

#pragma DATA_SECTION(normalOperation, "NORMALOP")

void
normalOperation ( void ){
code here
}

In the linker:

MEMORY
{
PAGE 0:
JUMPTBL    : origin = 0x338000, length = 0x000064
}

SECTIONS
{
NORMALOP        : > JUMPTBL    PAGE = 0
}

When I run this, I get the warning of "#824-D pragma DATA_SECTION can only be applied to a file level symbol definition, not "normalOperation" (declared at line 402) main.c" and no pointer in the specified memory section.

What is the correct way to place a function pointer in flash memory?

  • 0
    Expert 1806 points

    What about

    #pragma DATA_SECTION(ptr_to_normalOperation, "NORMALOP")

    void (*ptr_to_normalOperation)(void) = normalOperation;

    Best regards

    Johannes

  • 0 in reply to Johannes von Löwis
    Prodigy 160 points

    When I enter that instead, the code will compile and run, but no pointer gets written to flash.

  • 0 in reply to Christopher Mounce
    Expert 1806 points

    Maybe

    void (* const ptr_to_normalOperation)(void) = normalOperation;

    does the trick.

    Regards

    Johannes

  • 0 in reply to Johannes von Löwis
    Prodigy 160 points

    This stores the address of where normalOperation starts, and it stores it at the correct location, but does not handle the actual jump, so I can't use it as a jump table to jump to various functions. I feel like we're really close.

  • 0 in reply to Christopher Mounce
    Expert 1806 points

    Hi Christopher,

    I'm afraid I don't know what exactly you want to do.

    If you want to have a table of function pointers it would look like this:

    void (* const function_table[4])(void) = {
      normalOperation,
      foo,
      bar,
      NULL
    };

    In order to call the i-th function from the table you would write

    function_table[i]();

    In order to call normalOperation, you would write

    function_table[0]();

    You will need to write code that decides which of the functions of the table have to be called and actually does the call(s).

    Best regards

    Johannes

  • 0 in reply to Johannes von Löwis
    Prodigy 160 points

    After some more trial and error, I found the following code worked out for me for jumping directly to specific functions:

    #pragma CODE_SECTION(jumpTable, "JUMPTABLE")
    void jumpTable(void){
    normalOperation();
    anyOtherfunctions();
    ...etc
    }
    or alternatively 
    asm(" LB 0xHEXADDRESS"); if you're trying to branch to a specific address instead of a function
    In the linker file:
    Under Memory:
     JUMPTBL    : origin = 0x338000, length = 0x000064 
    Under sections:
    JUMPTABLE : > JUMPTBL    PAGE = 0
    Since I knew the base address, and each jump was 2 lines of assembly, I could put a bunch of function calls back to back that I could call from anywhere. Not just function pointers, but actual jumps to the function or address desired. Hope this helps someone else!