TinyTesla USB interruptor firmware: On-Time extension

[KrisPringle]

Hi all,

I'm using profdc9's interrupter from his PCB pack, and it uses the firmware from the tiny Tesla USB interrupter. However, I'd like to use this to drive an SSTC and not a DRSSTC so the default on times and duty cycle not very optimal, they're only at about 30 uS. I'd like to significantly extend the on-time. Is anyone familiar enough with the firmware to help me? The newer SD card interrupter has an easy way to modify the on-time but it doesn't seem as straightforward here.

The on time seems to be determined here (?) in "util.c".

Code: [Select]

void noteOn1() {
TCNT1 = 0;
unsigned int freq = midiFreq(cNote1);
if (freq == 0) return;
unsigned long period_us = 1000000UL / freq;
unsigned long on_time = period_us / 32;
on_time = on_time * cVel1 / 127;
if (on_time > 100) on_time = 100;
ot_cycles1 = 4 * on_time + on_time / 8;
period_us -= on_time;

unsigned long p_cycles = 16 * period_us + (period_us / 2);

if (p_cycles / 32 < 0x100) {
TCCR1 = _BV(CS11) | _BV(CS12); // 1:32
p_cycles /= 32;
} else if (p_cycles / 64 < 0x100) {
TCCR1 = _BV(CS10) | _BV(CS11) | _BV(CS12); // 1:64
p_cycles /= 64;
} else if (p_cycles / 256 < 0x100) {
TCCR1 = _BV(CS10) | _BV(CS13); // 1:256
p_cycles /= 256;
} else if (p_cycles / 1024 < 0x100) {
TCCR1 = _BV(CS10) | _BV(CS11) | _BV(CS13); // 1:1024
p_cycles /= 1024;
} else {
return;
}

OCR1A = p_cycles;
TIMSK |= _BV(OCIE1A);
}
I tried just arbitrarily setting on_time to 500 but it didn't appear to make a difference which makes me think I must be missing something.

The firmware is available here https://onetesla.com/media/SDinterrupter.zip, I appreciate any help!