BizHawk/BizHawk.Emulation.Cores/Consoles/Coleco/SN76489col.cs

using System;

using BizHawk.Common;
using BizHawk.Common.NumberExtensions;

namespace BizHawk.Emulation.Cores.ColecoVision
{
	public sealed class SN76489col
	{
		private short current_sample;

		public SN76489col()
		{
			Reset();
		}

		public byte[] Chan_vol = new byte[4];
		public ushort[] Chan_tone = new ushort[4];

		public int chan_sel;
		public bool vol_tone;
		public bool noise_type;
		public int noise_rate;
		public bool noise_bit;

		private int psg_clock;

		private int clock_A, clock_B, clock_C;

		private bool A_up, B_up, C_up;

		private int noise_clock;
		private int noise;

		private static readonly byte[] LogScale = { 255, 203, 161, 128, 102, 86, 64, 51, 40, 32, 26, 20, 16, 13, 10, 0 };

		public void Reset()
		{
			clock_A = clock_B = clock_C = 0x1000;
			noise_clock = 0x10;
			chan_sel = 0;

			// reset the shift register
			noise = 0x40000;
		}

		public int Sample()
		{
			return current_sample;
		}

		public void SyncState(Serializer ser)
		{
			ser.BeginSection("SN76489");

			ser.Sync(nameof(Chan_vol), ref Chan_vol, false);
			ser.Sync(nameof(Chan_tone), ref Chan_tone, false);

			ser.Sync("Chan_sel", ref chan_sel);
			ser.Sync(nameof(vol_tone), ref vol_tone);
			ser.Sync(nameof(noise_type), ref noise_type);
			ser.Sync(nameof(noise_rate), ref noise_rate);

			ser.Sync("Clock_A", ref clock_A);
			ser.Sync("Clock_B", ref clock_B);
			ser.Sync("Clock_C", ref clock_C);
			ser.Sync(nameof(noise_clock), ref noise_clock);
			ser.Sync(nameof(noise_bit), ref noise_bit);

			ser.Sync(nameof(psg_clock), ref psg_clock);

			ser.Sync(nameof(A_up), ref A_up);
			ser.Sync(nameof(B_up), ref B_up);
			ser.Sync(nameof(C_up), ref C_up);
			ser.Sync(nameof(noise), ref noise);

			ser.Sync(nameof(current_sample), ref current_sample);

			ser.EndSection();
		}

		public byte ReadReg()
		{
			// not used, reading not allowed, just return 0xFF
			return 0xFF;
		}

		public void WriteReg(byte value)
		{
			// if bit 7 is set, change the latch, otherwise modify the currently latched register
			if (value.Bit(7))
			{
				chan_sel = (value >> 5) & 3;
				vol_tone = value.Bit(4);

				if (vol_tone)
				{
					Chan_vol[chan_sel] = (byte)(value & 0xF);
				}
				else
				{
					if (chan_sel < 3)
					{
						Chan_tone[chan_sel] &= 0x3F0;
						Chan_tone[chan_sel] |= (ushort)(value & 0xF);
					}
					else
					{
						noise_type = value.Bit(2);
						noise_rate = value & 3;

						// reset the shift register
						noise = 0x40000;
					}
				}
			}
			else
			{
				if (vol_tone)
				{
					Chan_vol[chan_sel] = (byte)(value & 0xF);
				}
				else
				{
					if (chan_sel < 3)
					{
						Chan_tone[chan_sel] &= 0xF;
						Chan_tone[chan_sel] |= (ushort)((value & 0x3F) << 4);
					}
					else
					{
						noise_type = value.Bit(2);
						noise_rate = value & 3;

						// reset the shift register
						noise = 0x40000;
					}
				}
			}
		}

		public void generate_sound(int cycles_to_do)
		{
			// there are 16 cpu cycles for every psg cycle
			for (int i = 0; i < cycles_to_do; i++)
			{
				psg_clock++;

				if (psg_clock == 16)
				{
					psg_clock = 0;

					clock_A--;
					clock_B--;
					clock_C--;
					noise_clock--;

					// clock noise
					if (noise_clock == 0)
					{
						noise_bit = noise.Bit(0);
						if (noise_type)
						{
							int bit = (noise & 1) ^ ((noise >> 1) & 1);
							noise = noise >> 1;
							noise |= bit << 14;
							
						}
						else
						{
							int bit = noise & 1;
							noise = noise >> 1;
							noise |= bit << 14;
						}

						if (noise_rate == 0)
						{
							noise_clock = 0x10;
						}
						else if (noise_rate == 1)
						{
							noise_clock = 0x20;
						}
						else if (noise_rate == 2)
						{
							noise_clock = 0x40;
						}
						else
						{
							noise_clock = Chan_tone[2] + 1;
						}

						noise_clock *= 2;					
					}
					
					if (clock_A == 0)
					{
						A_up = !A_up;
						clock_A = Chan_tone[0] + 1;
					}

					if (clock_B == 0)
					{
						B_up = !B_up;
						clock_B = Chan_tone[1] + 1;
					}

					if (clock_C == 0)
					{
						C_up = !C_up;
						clock_C = Chan_tone[2] + 1;
					}

					// now calculate the volume of each channel and add them together
					// the magic number 42 is to make the volume comparable to the MSG volume
					int v;
	
					v = (short)(A_up ? LogScale[Chan_vol[0]] * 42 : 0);
					 
					v += (short)(B_up ? LogScale[Chan_vol[1]] * 42 : 0);

					v += (short)(C_up ? LogScale[Chan_vol[2]] * 42 : 0);

					v += (short)(noise_bit ? LogScale[Chan_vol[3]] * 42 : 0);

					current_sample = (short)v;
				}
			}
		}
	}
}