3D Digital Stereo Ixus 55 (Part 4: The Software)

As already mentioned in the introduction, I wanted to use CHDK or SDM on this camera but without having to use an external switch connected via USB. To achieve this I studied the source code of SDM carefully (Thanks David for making it public!) and rewrote the internal synch routine as follows and added it to the standard Allbest CHDK branch:

void wait_until_remote_button_is_released(void)
{
asm volatile ("STMFD SP!, {R0-R11,LR}\n"); // store R0-R11 and LR in stack

#define DELAY_TIMEOUT 10000
#define KBD_MASK 0x4
int tick;
long z, *x;

debug_led(1);
_kbd_pwr_on();
tick=get_tick_count();

do {
z = physw_status[2] & KBD_MASK;
x = (void*)0xc0220208;
_kbd_read_keys_r2(physw_status);

}
while( (!z) && ((int)get_tick_count()-tick < DELAY_TIMEOUT));

_kbd_pwr_off();

debug_led(0);
if (fd>=0) close (fd);

asm volatile ("LDMFD SP!, {R0-R11,LR}\n");
}


This way, the cameras do not wait for the external USB switch to be released but the shutter fires after the nomal shutter switch has been released. The shoot sequence therefore is pretty straightforward:
1. Half press the shutter to focus
2. Full press the shutter until both blue LEDs light up
3. Release the shutter and a highly synchronized pair of pictures is taken.

I havent measured the synch systematically yet because I don't have a CRT monitor anymore to be able to use the Camera Synch Tester.