Re: [avr-gcc-list] End of program symbol

[Adam Dunkels]

Pink Boy wrote:
> Adam sez,
>
> > How about using a ROM/PROGMEM array in which dynamic code is loaded
> > instead of putting it after _etext? This is what we are doing in
> > the Contiki OS. One nice thing with this is that you can decide
> > beforehand how much space you'd like to reserve for the dynamic
> > code (and you'll be notified by the linker if there isn't enough
> > space in ROM).
>  
> How do you align the array with the 64/128 byte flash sector 
> boundries?

I simply over-allocate the array and make sure that pointers to 
allocations are properly aligned. I.e., for a 512 byte alignment, I add 
512 bytes to the size of the array and round the pointer to the 
allocated memory upwards to the next 512 byte boundary. Something along 
the lines of this:

static const PROGMEM unsigned char textmemory[SIZE + 0x200];

static PROGMEM char *allocate_memory() {
  return (char *)
    ((unsigned long)&textmemory[0] & 0xfffffe00) +
    (((unsigned long)&textmemory[0] & 0x1ff) == 0? 0: 0x200);
}

I lose 512 bytes of ROM, but I don't need to fiddle with linker scripts, 
sections, or #defines.

/adam
--
Adam Dunkels, Swedish Institute of Computer Science
http://www.sics.se/~adam/