feat(audio): add square wave channel with sweep and envelope
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dualfroz committed
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5342fc360f
commit
96d25c7c39
1 file changed
+233
@@ -0,0 +1,233 @@
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using System.IO;
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namespace GameBoy.Audio
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{
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internal sealed class SquareChannel
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{
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private static readonly byte[][] DutyTable =
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{
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new byte[] { 0, 0, 0, 0, 0, 0, 0, 1 },
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new byte[] { 1, 0, 0, 0, 0, 0, 0, 1 },
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new byte[] { 1, 0, 0, 0, 0, 1, 1, 1 },
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new byte[] { 0, 1, 1, 1, 1, 1, 1, 0 }
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};
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private readonly bool hasSweep;
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private byte nrx0, nrx1, nrx2, nrx3, nrx4;
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private int frequencyTimer;
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private int dutyStep;
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private int duty;
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private bool enabled;
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private bool dacEnabled;
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private int lengthCounter;
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private bool lengthEnabled;
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private int volume;
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private int envelopePeriod;
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private bool envelopeAdd;
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private int envelopeTimer;
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private int sweepShadow;
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private int sweepTimer;
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private bool sweepEnabled;
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private int sweepPeriod;
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private bool sweepNegate;
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private int sweepShift;
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public SquareChannel(bool hasSweep)
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{
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this.hasSweep = hasSweep;
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}
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public bool Enabled => enabled;
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public bool DacEnabled => dacEnabled;
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private int Frequency => ((nrx4 & 0x07) << 8) | nrx3;
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public int Output() => enabled ? DutyTable[duty][dutyStep] * volume : 0;
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public float Analog() => dacEnabled ? (Output() / 15f * 2f - 1f) : 0f;
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public byte Read(int reg)
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{
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return reg switch
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{
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0 => nrx0,
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1 => nrx1,
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2 => nrx2,
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3 => nrx3,
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4 => nrx4,
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_ => 0xFF
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};
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}
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public void Write(int reg, byte value)
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{
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switch (reg)
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{
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case 0:
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nrx0 = value;
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break;
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case 1:
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nrx1 = value;
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duty = value >> 6;
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lengthCounter = 64 - (value & 0x3F);
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break;
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case 2:
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nrx2 = value;
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dacEnabled = (value & 0xF8) != 0;
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if (!dacEnabled)
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enabled = false;
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envelopePeriod = value & 0x07;
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envelopeAdd = (value & 0x08) != 0;
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break;
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case 3:
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nrx3 = value;
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break;
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case 4:
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nrx4 = value;
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lengthEnabled = (value & 0x40) != 0;
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if ((value & 0x80) != 0)
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Trigger();
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break;
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}
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}
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public void Step(int cycles)
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{
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frequencyTimer -= cycles;
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while (frequencyTimer <= 0)
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{
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frequencyTimer += (2048 - Frequency) * 4;
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dutyStep = (dutyStep + 1) & 7;
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}
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}
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public void ClockLength()
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{
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if (lengthEnabled && lengthCounter > 0)
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{
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lengthCounter--;
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if (lengthCounter == 0)
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enabled = false;
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}
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}
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public void ClockEnvelope()
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{
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if (envelopePeriod == 0)
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return;
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if (envelopeTimer > 0)
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envelopeTimer--;
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if (envelopeTimer == 0)
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{
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envelopeTimer = envelopePeriod;
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int next = volume + (envelopeAdd ? 1 : -1);
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if (next >= 0 && next <= 15)
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volume = next;
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}
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}
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public void ClockSweep()
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{
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if (!hasSweep)
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return;
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if (sweepTimer > 0)
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sweepTimer--;
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if (sweepTimer != 0)
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return;
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sweepTimer = sweepPeriod > 0 ? sweepPeriod : 8;
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if (!sweepEnabled || sweepPeriod == 0)
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return;
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int candidate = NextSweepFrequency();
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if (candidate <= 2047 && sweepShift > 0)
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{
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sweepShadow = candidate;
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nrx3 = (byte)(candidate & 0xFF);
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nrx4 = (byte)((nrx4 & 0xF8) | ((candidate >> 8) & 0x07));
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NextSweepFrequency();
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}
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}
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private int NextSweepFrequency()
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{
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int delta = sweepShadow >> sweepShift;
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int candidate = sweepNegate ? sweepShadow - delta : sweepShadow + delta;
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if (candidate > 2047)
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enabled = false;
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return candidate;
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}
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private void Trigger()
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{
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enabled = dacEnabled;
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if (lengthCounter == 0)
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lengthCounter = 64;
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frequencyTimer = (2048 - Frequency) * 4;
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envelopeTimer = envelopePeriod;
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volume = nrx2 >> 4;
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if (hasSweep)
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{
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sweepShadow = Frequency;
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sweepPeriod = (nrx0 >> 4) & 0x07;
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sweepNegate = (nrx0 & 0x08) != 0;
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sweepShift = nrx0 & 0x07;
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sweepTimer = sweepPeriod > 0 ? sweepPeriod : 8;
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sweepEnabled = sweepPeriod > 0 || sweepShift > 0;
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if (sweepShift > 0)
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NextSweepFrequency();
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}
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}
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public void PowerOff()
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{
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nrx0 = nrx1 = nrx2 = nrx3 = nrx4 = 0;
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frequencyTimer = 0;
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dutyStep = 0;
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duty = 0;
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enabled = false;
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dacEnabled = false;
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lengthCounter = 0;
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lengthEnabled = false;
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volume = 0;
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envelopePeriod = 0;
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envelopeAdd = false;
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envelopeTimer = 0;
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sweepShadow = 0;
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sweepTimer = 0;
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sweepEnabled = false;
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sweepPeriod = 0;
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sweepNegate = false;
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sweepShift = 0;
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}
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public void SaveState(BinaryWriter w)
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{
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w.Write(nrx0); w.Write(nrx1); w.Write(nrx2); w.Write(nrx3); w.Write(nrx4);
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w.Write(frequencyTimer); w.Write(dutyStep); w.Write(duty);
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w.Write(enabled); w.Write(dacEnabled);
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w.Write(lengthCounter); w.Write(lengthEnabled);
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w.Write(volume); w.Write(envelopePeriod); w.Write(envelopeAdd); w.Write(envelopeTimer);
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w.Write(sweepShadow); w.Write(sweepTimer); w.Write(sweepEnabled);
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w.Write(sweepPeriod); w.Write(sweepNegate); w.Write(sweepShift);
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}
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public void LoadState(BinaryReader r)
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{
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nrx0 = r.ReadByte(); nrx1 = r.ReadByte(); nrx2 = r.ReadByte(); nrx3 = r.ReadByte(); nrx4 = r.ReadByte();
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frequencyTimer = r.ReadInt32(); dutyStep = r.ReadInt32(); duty = r.ReadInt32();
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enabled = r.ReadBoolean(); dacEnabled = r.ReadBoolean();
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lengthCounter = r.ReadInt32(); lengthEnabled = r.ReadBoolean();
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volume = r.ReadInt32(); envelopePeriod = r.ReadInt32(); envelopeAdd = r.ReadBoolean(); envelopeTimer = r.ReadInt32();
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sweepShadow = r.ReadInt32(); sweepTimer = r.ReadInt32(); sweepEnabled = r.ReadBoolean();
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sweepPeriod = r.ReadInt32(); sweepNegate = r.ReadBoolean(); sweepShift = r.ReadInt32();
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}
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}
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}
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