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