BizHawk/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/NES-EVENT.cs

using System.Collections.Generic;
using BizHawk.Common;
using BizHawk.Common.NumberExtensions;

// https://wiki.nesdev.com/w/index.php/INES_Mapper_105
namespace BizHawk.Emulation.Cores.Nintendo.NES
{
	//AKA mapper 105
	internal sealed class NES_EVENT : NesBoardBase
	{
		//configuration
		int prg_bank_mask_16k;

		//regenerable state
		int[] prg_banks_16k = new int[2];

		//state
		MMC1.MMC1_SerialController scnt;
		bool c000_swappable, prg_32k_mode;
		bool irq_enable;
		int prg_a, prg_b;
		int init_sequence;
		bool chip_select;
		bool wram_disable;

		int irq_count;
		int irq_destination;
		bool irq_pending;

		[MapperProp]
		public bool Dipswitch1 = false;

		[MapperProp]
		public bool Dipswitch2 = true;

		[MapperProp]
		public bool Dipswitch3 = false;

		[MapperProp]
		public bool Dipswitch4 = false;

		private List<bool> Switches =>
			new List<bool>
			{
				{ Dipswitch1 },
				{ Dipswitch2 },
				{ Dipswitch3 },
				{ Dipswitch4 }
			};

		public int IrqDestination
		{
			get
			{
				SyncIRQDestination();
				return irq_destination;
			}
		}

		private void SyncIRQDestination()
		{
			//0b001D_CBAx_xxxx_xxxx_xxxx_xxxx_xxxx_xxxx

			int val = 0;
			for (int i = 0; i < Switches.Count; i++)
			{
				val <<= 1;
				if (Switches[i])
				{
					val |= 1;
				}
			}

			irq_destination = 0x20000000 | (val << 25);
		}

		public override void SyncState(Serializer ser)
		{
			base.SyncState(ser);

			scnt.SyncState(ser);
			ser.Sync(nameof(c000_swappable), ref c000_swappable);
			ser.Sync("prg_16k_mode", ref prg_32k_mode);
			ser.Sync(nameof(irq_enable), ref irq_enable);
			ser.Sync(nameof(irq_pending), ref irq_pending);
			ser.Sync(nameof(irq_count), ref irq_count);
			ser.Sync(nameof(prg_a), ref prg_a);
			ser.Sync(nameof(prg_b), ref prg_b);
			ser.Sync(nameof(init_sequence), ref init_sequence);
			ser.Sync(nameof(chip_select), ref chip_select);
			ser.Sync(nameof(wram_disable), ref wram_disable);
			ser.Sync(nameof(prg_banks_16k), ref prg_banks_16k, false);
			if (ser.IsReader) Sync();
		}

		public override bool Configure(EDetectionOrigin origin)
		{
			switch (Cart.BoardType)
			{
				case "MAPPER105":
					break;
				case "NES-EVENT":
					AssertPrg(256); AssertChr(0); AssertVram(8); AssertWram(8);
					break;
				default:
					return false;
			}

			prg_bank_mask_16k = Cart.PrgSize / 16 - 1;
			init_sequence = 0;

			SetMirrorType(EMirrorType.Vertical);

			scnt = new MMC1.MMC1_SerialController
			{
				WriteRegister = SerialWriteRegister,
				Reset = SerialReset
			};

			InitValues();

			return true;
		}

		void SerialReset()
		{
			prg_32k_mode = true;
			c000_swappable = true;
		}

		void Sync()
		{
			SyncIRQDestination();
			SyncIRQ();

			if (init_sequence != 2)
			{
				// prg banks locked to first 32k of first 128k chip
				prg_banks_16k[0] = 0;
				prg_banks_16k[1] = 1;
			}
			else
			{
				if (!chip_select)
				{
					//use prg banks in first 128k as indicated by prg_a reg
					prg_banks_16k[0] = prg_a * 2;
					prg_banks_16k[1] = prg_a * 2 + 1;
				}
				else
				{
					if (!prg_32k_mode)
					{
						//use prg banks in second 128k (add 8*16k as offset) in 32k mode, as determined by prg_b reg
						prg_banks_16k[0] = ((prg_b & ~1) & 7) + 8;
						prg_banks_16k[1] = ((prg_b & ~1) & 7) + 9;
					}
					else
					{
					//((these arent tested, i think...))
						//"use second 128k"
						if (!c000_swappable)
						{
							prg_banks_16k[0] = 8;
							prg_banks_16k[1] = prg_b + 8;
						}
						else
						{
							prg_banks_16k[0] = prg_b + 8;
							prg_banks_16k[1] = 15; //last bank of second 128k
						}
					}
				}
			}

			prg_banks_16k[0] &= prg_bank_mask_16k;
			prg_banks_16k[1] &= prg_bank_mask_16k;
		}

		void SerialWriteRegister(int addr, int value)
		{
			switch (addr)
			{
				case 0: //8000-9FFF
					switch (value & 3)
					{
						case 0: SetMirrorType(EMirrorType.OneScreenA); break;
						case 1: SetMirrorType(EMirrorType.OneScreenB); break;
						case 2: SetMirrorType(EMirrorType.Vertical); break;
						case 3: SetMirrorType(EMirrorType.Horizontal); break;
					}
					c000_swappable = value.Bit(2);
					prg_32k_mode = value.Bit(3);
					Sync();
					break;
				case 1: //A000-BFFF
					{
						irq_enable = !value.Bit(4);

						//Acknowledge IRQ
						if (!irq_enable)
						{
							irq_count = 0;
							irq_pending = false;
						}

						if (init_sequence == 0 && irq_enable)
						{
							init_sequence = 1;
						}
						else if  (init_sequence == 1 && !irq_enable)
						{
							init_sequence = 2;
						}

						chip_select = value.Bit(3);
						prg_a = (value >> 1) & 3;
						Sync();
						break;
					}
				case 2: //C000-DFFF
					//unused
					break;
				case 3: //E000-FFFF
					prg_b = value & 0xF;
					wram_disable = value.Bit(4);
					Sync();
					break;
			}
			//board.NES.LogLine("mapping.. chr_mode={0}, chr={1},{2}", chr_mode, chr_0, chr_1);
			//board.NES.LogLine("mapping.. prg_mode={0}, prg_slot{1}, prg={2}", prg_mode, prg_slot, prg);
		}

		public override void WriteWram(int addr, byte value)
		{
			if (!wram_disable)
			{
				base.WriteWram(addr, value);
			}
		}

		public override byte ReadWram(int addr)
		{
			return wram_disable ? NES.DB : base.ReadWram(addr);
		}

		public override void NesSoftReset()
		{
			InitValues();
			base.NesSoftReset();
		}

		private void InitValues()
		{
			AutoMapperProps.Apply(this);

			irq_enable = false;
			init_sequence = 0;
			irq_count = 0;

			Sync();
		}

		public override void WritePrg(int addr, byte value)
		{
			scnt.Write(addr, value);
		}


		public override byte ReadPrg(int addr)
		{
			int bank_16k = addr >> 14;
			int ofs = addr & ((1 << 14) - 1);
			bank_16k = prg_banks_16k[bank_16k];
			addr = (bank_16k << 14) | ofs;
			return Rom[addr];
		}

		public override void ClockCpu()
		{
			if (irq_enable)
			{
				ClockIRQ();
			}
		}

		private void ClockIRQ()
		{
			irq_count++;
			if (irq_count >= irq_destination)
			{
				irq_enable = false;
				irq_pending = true;
			}

			SyncIRQ();
		}

		private void SyncIRQ()
		{
			SyncIRQ(irq_pending);
		}
	}
}