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Added the APU Class and wired it all up ready for the maths

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Marc Parsons
2026-05-14 21:27:05 +01:00
parent 708c1ba458
commit cafcf625ad
6 changed files with 549 additions and 20 deletions
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224
Core/Audio/SmsApu.cs Normal file
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@@ -0,0 +1,224 @@
using Core.Interfaces;
namespace Core.Audio
{
public class SmsApu
{
// Your existing variables
public ushort[] Registers { get; private set; } = new ushort[8];
private int _latchedRegister = 0;
// THE NEW CONNECTION: Where we send the audio!
public IAudioDevice AudioDevice { get; set; }
// --- TIMING VARIABLES ---
private const double ClockRate = 3579545.0; // NTSC Master System speed
private const int SampleRate = 44100; // CD-Quality Audio
private double _cyclesPerSample = ClockRate / SampleRate;
private double _sampleCycleTracker = 0;
private int _psgCycleTracker = 0;
// --- SYNTHESIZER STATE ---
private int[] _counters = new int[4];
private int[] _polarities = new int[4] { 1, 1, 1, 1 }; // 1 = High, -1 = Low
private ushort _lfsr = 0x8000; // Linear Feedback Shift Register (For Noise)
// The SN76489 Volume Table reduces amplitude by exactly 2 decibels per step.
private static readonly float[] VolumeTable = {
1.0f, 0.7943f, 0.6309f, 0.5011f, 0.3981f, 0.3162f, 0.2511f, 0.1995f,
0.1584f, 0.1258f, 0.1000f, 0.0794f, 0.0630f, 0.0501f, 0.0398f, 0.0f
};
public SmsApu()
{
Registers[1] = 0x0F;
Registers[3] = 0x0F;
Registers[5] = 0x0F;
Registers[7] = 0x0F;
}
// [KEEP YOUR EXISTING WritePort7F METHOD HERE]
public void Update(int tStates)
{
for (int i = 0; i < tStates; i++)
{
// 1. The hardware chip only updates its wave counters every 16 CPU cycles
_psgCycleTracker++;
if (_psgCycleTracker >= 16)
{
_psgCycleTracker = 0;
TickChannels();
}
// 2. We only want to generate 44,100 samples per second, not 3.58 million!
_sampleCycleTracker++;
if (_sampleCycleTracker >= _cyclesPerSample)
{
_sampleCycleTracker -= _cyclesPerSample;
MixAndOutputSample();
}
}
}
private void TickChannels()
{
// --- TONE CHANNELS (0, 1, and 2) ---
for (int i = 0; i < 3; i++)
{
_counters[i]--;
if (_counters[i] <= 0)
{
// Reload the counter from the Tone Register.
// HARDWARE QUIRK: A tone register of 0 acts as 1024!
int tone = Registers[i * 2];
_counters[i] = (tone == 0) ? 1024 : tone;
// Flip the wave polarity! (This creates the vibration of the sound)
_polarities[i] *= -1;
}
}
// --- NOISE CHANNEL (3) ---
_counters[3]--;
if (_counters[3] <= 0)
{
// Noise rate depends on Bits 0-1 of Register 6
int shiftRate = Registers[6] & 0x03;
if (shiftRate == 0) _counters[3] = 0x10; // Fast
else if (shiftRate == 1) _counters[3] = 0x20; // Medium
else if (shiftRate == 2) _counters[3] = 0x40; // Slow
else _counters[3] = (Registers[4] == 0) ? 1024 : Registers[4]; // Linked to Tone 2!
// Shift the Noise LFSR
int tappedBit = _lfsr & 1;
_lfsr >>= 1;
if (tappedBit == 1)
{
bool isWhiteNoise = (Registers[6] & 0x04) != 0;
// The Sega Master System physically tapped bits 0 and 3 for its white noise
if (isWhiteNoise) _lfsr ^= 0x0009;
_lfsr |= 0x8000; // Inject the high bit
}
_polarities[3] = (tappedBit == 1) ? 1 : -1;
}
}
private void MixAndOutputSample()
{
// If the UI hasn't hooked up the speakers yet, just throw the audio away!
if (AudioDevice == null) return;
float sample = 0f;
// Mix Tone Channels 0, 1, 2
for (int i = 0; i < 3; i++)
{
// HARDWARE QUIRK: If the tone frequency is 1 or 0, the channel outputs a
// constant DC voltage instead of vibrating, meaning it is effectively silent.
if (Registers[i * 2] > 1)
{
sample += _polarities[i] * VolumeTable[Registers[(i * 2) + 1]];
}
}
// Mix Noise Channel 3
sample += _polarities[3] * VolumeTable[Registers[7]];
// Divide by 4 so all 4 channels together never exceed 1.0f (which would cause horrible distortion!)
sample /= 4.0f;
AudioDevice.AddSample(sample);
}
public void WritePort7F(byte value)
{
if ((value & 0x80) != 0)
{
// --- LATCH BYTE --- (Bit 7 is 1)
// Bits 4-6 contain the Register Index (0 to 7)
_latchedRegister = (value >> 4) & 0x07;
// Bits 0-3 contain the lower 4 bits of data
int data = value & 0x0F;
if (_latchedRegister % 2 != 0 || _latchedRegister == 6)
{
// Volume registers (1, 3, 5, 7) and Noise Control (6) only hold 4 bits total.
// We completely overwrite them.
Registers[_latchedRegister] = (ushort)data;
}
else
{
// Tone registers (0, 2, 4) hold 10 bits.
// A Latch byte ONLY overwrites the bottom 4 bits and leaves the top 6 alone!
Registers[_latchedRegister] = (ushort)((Registers[_latchedRegister] & 0x03F0) | data);
}
}
else
{
// --- DATA BYTE --- (Bit 7 is 0)
// Bits 0-5 contain the upper 6 bits of data for the currently latched Tone register
int data = value & 0x3F;
if (_latchedRegister % 2 == 0 && _latchedRegister != 6)
{
// Update the top 6 bits of the 10-bit Tone register
Registers[_latchedRegister] = (ushort)((Registers[_latchedRegister] & 0x000F) | (data << 4));
}
else
{
// If a Data Byte is sent to a Volume or Noise register, it just overwrites the lower 4 bits again
Registers[_latchedRegister] = (ushort)(data & 0x0F);
}
}
}
}
}
//using System;
//namespace Core.Audio
//{
// public class SmsApu
// {
// // The 8 internal registers of the PSG
// // 0: Tone 0 Frequency (10 bits)
// // 1: Tone 0 Volume (4 bits)
// // 2: Tone 1 Frequency (10 bits)
// // 3: Tone 1 Volume (4 bits)
// // 4: Tone 2 Frequency (10 bits)
// // 5: Tone 2 Volume (4 bits)
// // 6: Noise Control (3 bits)
// // 7: Noise Volume (4 bits)
// public ushort[] Registers { get; private set; } = new ushort[8];
// // Remembers which register the CPU is currently talking to
// private int _latchedRegister = 0;
// public SmsApu()
// {
// // Volumes default to 0x0F (Silence! 0 = max volume, 15 = off)
// Registers[1] = 0x0F;
// Registers[3] = 0x0F;
// Registers[5] = 0x0F;
// Registers[7] = 0x0F;
// }
// }
//}

6
Core/Core.csproj
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@@ -6,12 +6,6 @@
<Nullable>enable</Nullable>
</PropertyGroup>
<ItemGroup>
<Compile Remove="Audio\**" />
<EmbeddedResource Remove="Audio\**" />
<None Remove="Audio\**" />
</ItemGroup>
<ItemGroup>
<Folder Include="Cpu\" />
</ItemGroup>

4
Core/Interfaces/IAudioDevice.cs
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@@ -2,7 +2,7 @@
{
public interface IAudioDevice
{
// Now accepts the Beeper state + 3 AY frequencies + 3 AY volumes
void AddSample(bool isHigh, float freqA, float volA, float freqB, float volB, float freqC, float volC);
// Accepts a single, fully-mixed audio sample (usually between -1.0f and 1.0f)
void AddSample(float sample);
}
}

21
Core/Io/SmsIoBus.cs
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@@ -1,4 +1,5 @@
using Core.Interfaces;
using Core.Audio;
using Core.Interfaces;
using Core.Video;
namespace Core.Io
@@ -6,7 +7,7 @@ namespace Core.Io
public class SmsIoBus : IIoBus
{
public SmsVdp VideoProcessor { get; set; }
// public Psg AudioProcessor { get; set; }
public SmsApu AudioProcessor { get; set; }
// Joypad State (0xFF means no buttons pressed - the SMS uses Active-Low logic!)
public byte Joypad1Keyboard = 0xFF;
@@ -42,15 +43,19 @@ namespace Core.Io
{
byte lowerPort = (byte)(port & 0xFF);
if (lowerPort >= 0x40 && lowerPort <= 0x7F)
// Audio Ports
if (lowerPort == 0x7E || lowerPort == 0x7F)
{
// PSG Audio Write (Usually written exactly to 0x7F)
// AudioProcessor.WriteData(value);
AudioProcessor.WritePort7F(value);
}
else if (lowerPort >= 0x80 && lowerPort <= 0xBF)
// Video Ports
else if (lowerPort == 0xBE)
{
if ((lowerPort & 0x01) == 0) VideoProcessor.WriteDataPort(value);
else VideoProcessor.WriteControlPort(value);
VideoProcessor.WriteDataPort(value);
}
else if (lowerPort == 0xBF)
{
VideoProcessor.WriteControlPort(value);
}
else if (lowerPort <= 0x3F)
{

14
Core/SmsMachine.cs
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@@ -1,6 +1,8 @@
using Core.Cpu;
using Core.Io;
using Core.Memory;
using Core.Video;
using Core.Audio;
using System;
using System.IO;
using System.Collections.Generic;
@@ -12,7 +14,8 @@ namespace Core
public Z80 Cpu { get; private set; }
public SmsMemoryBus MemoryBus { get; private set; }
public SmsIoBus IoBus { get; private set; }
public Core.Video.SmsVdp VideoProcessor { get; private set; }
public SmsVdp VideoProcessor { get; private set; }
public SmsApu AudioProcessor { get; private set; }
public ushort? Breakpoint { get; set; } = null;
// NTSC SMS T-States per frame
@@ -21,8 +24,9 @@ namespace Core
public SmsMachine()
{
MemoryBus = new SmsMemoryBus();
VideoProcessor = new Core.Video.SmsVdp();
IoBus = new SmsIoBus { VideoProcessor = this.VideoProcessor };
VideoProcessor = new SmsVdp();
AudioProcessor = new SmsApu();
IoBus = new SmsIoBus { VideoProcessor = this.VideoProcessor, AudioProcessor = this.AudioProcessor };
Cpu = new Z80(MemoryBus, IoBus);
}
@@ -50,13 +54,15 @@ namespace Core
// 2. Tell the VDP to catch up
VideoProcessor.Update(cycles);
AudioProcessor.Update(cycles);
// 3. Check if the VDP is begging for attention!
if (VideoProcessor.InterruptPending && Cpu.IFF1)
{
int intCycles = Cpu.RequestInterrupt();
tStatesThisFrame += intCycles;
VideoProcessor.Update(intCycles); // Keep VDP perfectly in sync
VideoProcessor.Update(intCycles);
AudioProcessor.Update(intCycles);
}
// 4. THE RESTORED BREAKPOINT TRAP