NES - start mapper 50, but it doesn't work

BizHawk.Emulation/BizHawk.Emulation.csproj

@@ -177,6 +177,7 @@
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper046.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper243.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper246.cs" />
+    <Compile Include="Consoles\Nintendo\NES\Boards\Mapper50.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper60.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper61.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper62.cs" />

BizHawk.Emulation/Consoles/Nintendo/NES/Boards/Mapper50.cs

@@ -0,0 +1,80 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace BizHawk.Emulation.Consoles.Nintendo
+{
+	class Mapper50 : NES.NESBoardBase
+	{
+		//http://wiki.nesdev.com/w/index.php/INES_Mapper_050
+
+		byte prg_bank;
+		int prg_bank_mask_8k;
+
+		public override bool Configure(NES.EDetectionOrigin origin)
+		{
+			//analyze board type
+			switch (Cart.board_type)
+			{
+				case "MAPPER050":
+					break;
+				default:
+					return false;
+			}
+			prg_bank = 0;
+			prg_bank_mask_8k = Cart.prg_size / 8 - 1;
+
+			return true;
+		}
+
+		public override void SyncState(Serializer ser)
+		{
+			ser.Sync("prg_bank", ref prg_bank);
+			base.SyncState(ser);
+		}
+
+		public override void WriteEXP(int addr, byte value)
+		{
+			addr &= 0x0120;
+			if (addr == 0x0020)
+			{
+				//byte low = (byte)((value >> 1) & 0x03);
+				//byte middle = (byte)(value & 0x01);
+				//byte high = (byte)((value >> 3) & 0x01);
+				//prg_bank = (byte)(low | (middle << 2) | (high << 3));
+
+				prg_bank = (byte)(((value & 1) << 2) | ((value & 2) >> 1) | ((value & 4) >> 1) | (value & 8));
+				
+				Console.WriteLine(prg_bank);
+			}
+			base.WriteEXP(addr, value);
+		}
+
+		public override byte ReadPRG(int addr)
+		{
+			if (addr < 0x2000)
+			{
+				return ROM[(0x08 * 0x2000) + (addr & 0x1FFF)];
+			}
+			else if (addr < 0x4000)
+			{
+				return ROM[(0x09 * 0x2000) + (addr & 0x1FFF)];
+			}
+			else if (addr < 0x6000)
+			{
+				int bank = (prg_bank & prg_bank_mask_8k);
+				return ROM[(bank * 0x2000) + (addr & 0x1FFF)];
+			}
+			else
+			{
+				return ROM[(0x0B * 0x2000) + (addr & 0x1FFF)];
+			}
+		}
+
+		public override byte ReadPPU(int addr)
+		{
+			return ROM[(0x0F * 0x2000) + (addr & 0x1FFF)];
+		}
+	}
+}