Simple blinky program and linker pruning

DavidZemon

Simple blinky program:

int main () {
    const int led = 0x10000;


    DIRA |= led;


    while (1) {
        OUTA ^= led;
        waitcnt(CLKFREQ / 4 + CNT);
    }
}

Hangs if I compile with `-ffunction-sections -fdata-sections` and link with `-Wl,--gc-sections` with cog memory model. Any idea why?

DavidZemon

For reference, here's the assembly output (with linker pruning off)

.text
    .balign    4
    .global    _main
_main
    mov    r7, DIRA
    mov    r6, .LC0
    or    r7, r6
    mov    DIRA, r7
.L2
    xor    OUTA,r6
    mov    r5, CNT
    rdlong    r7, .LC1
    shr    r7, #2
    add    r7, r5
    waitcnt    r7,#0
    jmp    #.L2
    .balign    4
.LC0
    long    65536
    .balign    4
.LC1
    long    __clkfreq

ersmith

If you do a "propeller-elf-objdump -d" on the generated elf files you'll see that everything is stripped out when "-mcog -gc-sections" is used. This is probably a bug in the way the -mcog linker script and startup files are set up. You can work around it by adding ''-Wl,-e -Wl,_main'' to the link command line -- this will stop the main() function from being stripped.

DavidZemon

Well, I doubt there are many folks using cog memory model anyway, so not the end of the world. but too bad for sure. Your post is a good work around for anyone that needs to actually use cog model for a project. For PropWare, I'm just going to have to do a check and, if the memory model is cog, disable linker pruning.