First of all, I'm working on porting the A530.
muttley, your XREF hint on the wiki page was very helpful. ^_^ I think I have boot.c right now, though I was unsure about the boot() function, so I followed your example. So hopefully you were right.

void boot()
{
long *canon_data_src = (void*)0xFFEDE3C0;
long *canon_data_dst = (void*)0x1900;
long canon_data_len = 0xB8D0;
long *canon_bss_start = (void*)0xD1D0;
long canon_bss_len = 0x91C70 - 0xD1D0;
[...]
The line for canon_data_src looked like this, so I'm not sure.

:
ROM:FFC0017C off_FFC0017C DCD unk_FFEDE3C0 ; DATA XREF: ROM:FFC0010
Other than that, I'm now in the same boat. I don't know where to start with lib.c, and I haven't found anything with IDA so far. the lib.c from the A540 source code has some helpful-looking comments, but I still can't figure out how to find the right values. (Some of them were commented out for some reason.

)
[commented out]
char *hook_raw_image_addr()
{
return (char*)0x105B8AC0; // OK (find on ".crw")
}
long hook_raw_size()
{
return 0x75A8F0; // OK (find on ".crw")
}
[commented out]
void *vid_get_bitmap_fb()
{
return (void*)0x103C79A0; // OK (find in _CreatePhysicalVram)
}
void *vid_get_viewport_fb()
{
return (void*)0x105F17A0; // OK (find on "VRAM Address : %p")
}
void *vid_get_viewport_fb_d()
{
return (void*)(*(int*)0x60BA0); // OK (find on "WBTblAdj.c")
}
[...]
Here is my stubs_entry_2.S, I guess I was lucky. (It does look very much like stubs_entry_2.S from the A540 source.) But I can't find free. I know there is information about it in signatures.h and IDA looks for it.
#include "stubs_asm.h"
NHSTUB(VbattGet, 0xFFC1C000) //found w/ IDA
NHSTUB(free, 0xFFC0A748) //not found yet (used FreeMemory)
//null stub (S2/S3 only apparently)
NHSTUB(SetZoomActuatorSpeedPercent, 0xFFC017E8) //used nullsub_1
I've modified things similarly to how muttley has (
A550 wiki page has more detail), and the rest is A560 code. When I compile it and try to load it the LCD turns off, the power led blinks off briefly, the green viewfinder led blinks on briefly, then the LCD comes on again with the regular firmware.
Could someone perhaps give us some hints on how to find these things for lib.c and stubs_entry_2.S?

And muttley, if you've made any further progress or have any further insight I'd love to hear it. I have a friend who is also interested in your A550 port for his camera.