bsnes/higan/fc/apu/dmc.cpp

auto APU::DMC::start() -> void {
  if(lengthCounter == 0) {
    readAddr = 0x4000 + (addrLatch << 6);
    lengthCounter = (lengthLatch << 4) + 1;
  }
}

auto APU::DMC::stop() -> void {
  lengthCounter = 0;
  dmaDelayCounter = 0;
  cpu.rdyLine(1);
  cpu.rdyAddr(false);
}

auto APU::DMC::clock() -> uint8 {
  uint8 result = dacLatch;

  if(dmaDelayCounter > 0) {
    dmaDelayCounter--;

    if(dmaDelayCounter == 1) {
      cpu.rdyAddr(true, 0x8000 | readAddr);
    } else if(dmaDelayCounter == 0) {
      cpu.rdyLine(1);
      cpu.rdyAddr(false);

      dmaBuffer = cpu.mdr();
      dmaBufferValid = true;
      lengthCounter--;
      readAddr++;

      if(lengthCounter == 0) {
        if(loopMode) {
          start();
        } else if(irqEnable) {
          irqPending = true;
          apu.setIRQ();
        }
      }
    }
  }

  if(--periodCounter == 0) {
    if(sampleValid) {
      int delta = (((sample >> bitCounter) & 1) << 2) - 2;
      uint data = dacLatch + delta;
      if((data & 0x80) == 0) dacLatch = data;
    }

    if(++bitCounter == 0) {
      if(dmaBufferValid) {
        sampleValid = true;
        sample = dmaBuffer;
        dmaBufferValid = false;
      } else {
        sampleValid = false;
      }
    }

    periodCounter = dmcPeriodTableNTSC[period];
  }

  if(lengthCounter > 0 && !dmaBufferValid && dmaDelayCounter == 0) {
    cpu.rdyLine(0);
    dmaDelayCounter = 4;
  }

  return result;
}

auto APU::DMC::power() -> void {
}

auto APU::DMC::reset() -> void {
  lengthCounter = 0;
  irqPending = 0;

  period = 0;
  periodCounter = dmcPeriodTableNTSC[0];
  irqEnable = 0;
  loopMode = 0;
  dacLatch = 0;
  addrLatch = 0;
  lengthLatch = 0;
  readAddr = 0;
  dmaDelayCounter = 0;
  bitCounter = 0;
  dmaBufferValid = 0;
  dmaBuffer = 0;
  sampleValid = 0;
  sample = 0;
}