69 lines
2.4 KiB
C#
69 lines
2.4 KiB
C#
using System;
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namespace Core.Audio
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{
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public class Ay38912
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{
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private readonly byte[] _registers = new byte[16];
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private byte _selectedRegister = 0;
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// The AY-3-8912 uses logarithmic volume, not linear!
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// This table converts the 0-15 register value into a precise float multiplier.
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private readonly float[] _volumeTable = {
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0.0000f, 0.0137f, 0.0205f, 0.0291f, 0.0423f, 0.0618f, 0.0847f, 0.1369f,
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0.1691f, 0.2647f, 0.3527f, 0.4499f, 0.5704f, 0.6873f, 0.8482f, 1.0000f
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};
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// --- Hardware Port Intercepts ---
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public void SelectRegister(byte register)
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{
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_selectedRegister = (byte)(register & 0x0F); // Only 16 registers exist
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}
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public void WriteRegister(byte value)
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{
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_registers[_selectedRegister] = value;
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}
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public byte ReadRegister()
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{
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return _registers[_selectedRegister];
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}
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// --- Audio Math Generators ---
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// The AY clock on a Spectrum 128 is 1.7734 MHz.
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// The chip divides this by 16 internally, giving a base clock of ~110,837 Hz.
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private float GetFrequency(int registerLow, int registerHigh)
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{
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int period = _registers[registerLow] | ((_registers[registerHigh] & 0x0F) << 8);
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if (period == 0) return 0f; // Prevent divide-by-zero
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return 110837.5f / period;
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}
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private float GetVolume(int volumeRegister)
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{
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byte vol = _registers[volumeRegister];
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// Bit 4 indicates if the channel is using the hardware Envelope generator.
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// For Version 1 of our chip, if the envelope is active, we will just
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// output half volume so the game doesn't go silent!
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if ((vol & 0x10) != 0)
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{
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return 0.5f;
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}
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return _volumeTable[vol & 0x0F];
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}
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// --- Public Data for your Audio Engine ---
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public float FreqA => GetFrequency(0, 1);
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public float FreqB => GetFrequency(2, 3);
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public float FreqC => GetFrequency(4, 5);
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// Register 7 is the Mixer. Bit 0, 1, and 2 turn the tone channels OFF when set to 1.
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public float VolA => (_registers[7] & 0x01) == 0 ? GetVolume(8) : 0f;
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public float VolB => (_registers[7] & 0x02) == 0 ? GetVolume(9) : 0f;
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public float VolC => (_registers[7] & 0x04) == 0 ? GetVolume(10) : 0f;
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}
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} |