bsnes/gba/apu/square1.cpp

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void APU::Square1::runsweep(bool update) {
if(sweep.enable == false) return;
sweep.negate = sweep.direction;
unsigned delta = shadowfrequency >> sweep.shift;
signed updatefrequency = shadowfrequency + (sweep.negate ? -delta : delta);
if(updatefrequency > 2047) {
enable = false;
} else if(sweep.shift && update) {
shadowfrequency = updatefrequency;
frequency = updatefrequency;
period = 2 * (2048 - frequency);
}
}
void APU::Square1::clocksweep() {
if(enable && sweep.frequency && --sweep.period == 0) {
sweep.period = sweep.frequency;
runsweep(1);
runsweep(0);
}
}
uint8 APU::Square1::read(unsigned addr) const {
switch(addr) {
case 0: return (sweep.shift << 0) | (sweep.direction << 3) | (sweep.frequency << 4);
case 1: return (duty << 6);
case 2: return (envelope.frequency << 0) | (envelope.direction << 3) | (envelope.volume << 4);
case 3: return 0;
case 4: return (counter << 6);
}
}
void APU::Square1::write(unsigned addr, uint8 byte) {
switch(addr) {
case 0: //NR10
if(sweep.negate && sweep.direction && !(byte & 0x08)) enable = false;
sweep.shift = byte >> 0;
sweep.direction = byte >> 3;
sweep.frequency = byte >> 4;
break;
case 1: //NR11
length = byte >> 0;
duty = byte >> 6;
break;
case 2: //NR12
envelope.frequency = byte >> 0;
envelope.direction = byte >> 3;
envelope.volume = byte >> 4;
if(envelope.dacenable() == false) enable = false;
break;
case 3: //NR13
frequency = (frequency & 0xff00) | (byte << 0);
break;
case 4: //NR14
frequency = (frequency & 0x00ff) | (byte << 8);
counter = byte >> 6;
initialize = byte >> 7;
if(initialize) {
enable = envelope.dacenable();
period = 2 * (2048 - frequency);
envelope.period = envelope.frequency;
volume = envelope.volume;
shadowfrequency = frequency;
sweep.period = sweep.frequency;
sweep.enable = sweep.period || sweep.shift;
sweep.negate = false;
if(sweep.shift) runsweep(0);
}
break;
}
}
void APU::Square1::power() {
envelope.frequency = 0;
envelope.direction = 0;
envelope.direction = 0;
envelope.period = 0;
sweep.shift = 0;
sweep.direction = 0;
sweep.frequency = 0;
sweep.enable = 0;
sweep.negate = 0;
sweep.period = 0;
enable = 0;
length = 0;
duty = 0;
frequency = 0;
counter = 0;
initialize = 0;
shadowfrequency = 0;
signal = 0;
output = 0;
period = 0;
phase = 0;
volume = 0;
}