nes mapper 168: racermate. not playable until special controller is emulated

BizHawk.Emulation/BizHawk.Emulation.csproj

@@ -167,6 +167,7 @@
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper132.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper156.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper164.cs" />
+    <Compile Include="Consoles\Nintendo\NES\Boards\Mapper168.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper176.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper178.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper180.cs" />

BizHawk.Emulation/Consoles/Nintendo/NES/Boards/Mapper168.cs

@@ -0,0 +1,111 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace BizHawk.Emulation.Consoles.Nintendo
+{
+	// RacerMate II
+	// 64KB PRGROM, 64KB CHRRAM(!), CHRRAM is battry backed (!!)
+	// the "ram protect" function is not emulated.  the notes i found said that it
+	// defaults to off, the control regs are write only, and cannot be reenabled.  so...
+
+	// todo: special controller, and IRQ is possibly wrong
+	public class Mapper168 : NES.NESBoardBase
+	{
+		int prg = 0;
+		int chr = 0;
+		int irqclock = 2048 * 3;
+
+		public override bool Configure(NES.EDetectionOrigin origin)
+		{
+			switch (Cart.board_type)
+			{
+				case "MAPPER168":
+				case "UNL-RACERMATE":
+					break;
+				default:
+					return false;
+			}
+			AssertPrg(64);
+			Cart.chr_size = 0; //AssertChr(0); //shitty dumps
+			Cart.vram_size = 64; //AssertVram(64); //shitty dumps
+			AssertWram(0);
+			//AssertBattery(true); // battery is handled directly
+			SetMirrorType(Cart.pad_h, Cart.pad_v);
+			return true;
+		}
+
+		public override byte ReadPRG(int addr)
+		{
+			if (addr >= 0x4000)
+				return ROM[addr + 0x8000];
+			else
+				return ROM[addr + (prg << 14)];
+		}
+
+		// the chr reg on hardware is supposedly bitscrambled and then inverted from
+		// what would be expected.  since it doesn't make a difference and i don't know
+		// of any clear source on what it's actually supposed to be, ignore.
+		int Scramble(int chr)
+		{
+			return chr;
+		}
+
+		public override void WritePRG(int addr, byte value)
+		{
+			if (addr < 0x4000)
+			{
+				chr = value & 15;
+				prg = value >> 6 & 3;
+			}
+			else if (addr == 0x7080) // ack
+				IRQSignal = false;
+			else if (addr == 0x7000) // start count
+				irqclock = 0;
+		}
+
+		public override byte ReadPPU(int addr)
+		{
+			if (addr < 0x1000)
+				return VRAM[addr | Scramble(0) << 12];
+			else if (addr < 0x2000)
+				return VRAM[(addr & 0xfff) | Scramble(chr) << 12];
+			else
+				return base.ReadPPU(addr);
+		}
+
+		public override void WritePPU(int addr, byte value)
+		{
+			if (addr < 0x1000)
+				VRAM[addr | Scramble(0) << 12] = value;
+			else if (addr < 0x2000)
+				VRAM[(addr & 0xfff) | Scramble(chr) << 12] = value;
+			else
+				base.WritePPU(addr, value);
+		}
+
+		public override byte[] SaveRam { get { return VRAM; } }
+
+		public override void SyncState(Serializer ser)
+		{
+			base.SyncState(ser);
+			ser.Sync("prg", ref prg);
+			ser.Sync("chr", ref chr);
+			ser.Sync("irqclock", ref irqclock);
+		}
+
+		public override void ClockPPU()
+		{
+			if (irqclock == 2048 * 3 - 1)
+			{
+				irqclock++;
+				IRQSignal = true;
+			}
+			else if (irqclock < 2048 * 3 - 1)
+			{
+				irqclock++;
+			}
+		}
+	}
+}