NES - add mapper 203, doesn't play the 35-1 properly, but it doesn't run in fceux as well, documentation may be off, or the ROM i used is bad (not a lot of info on good dumps for these types!)

BizHawk.Emulation/BizHawk.Emulation.csproj

@@ -157,6 +157,7 @@
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper180.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper193.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper200.cs" />
+    <Compile Include="Consoles\Nintendo\NES\Boards\Mapper203.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper207.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper226.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Mapper227.cs" />

BizHawk.Emulation/Consoles/Nintendo/NES/Boards/Mapper203.cs

@@ -0,0 +1,95 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace BizHawk.Emulation.Consoles.Nintendo
+{
+	class Mapper203 : NES.NESBoardBase
+	{
+		/*
+		Here are Disch's original notes:  
+		 ========================
+		 =  Mapper 203          =
+		 ========================
+ 
+		 Example Games:
+		 --------------------------
+		 35-in-1
+ 
+ 
+		 Registers:
+		 ---------------------------
+ 
+ 
+		   $8000-FFFF:  [PPPP PPCC]
+			 P = PRG Reg
+			 C = CHR Reg
+ 
+ 
+		 CHR Setup:
+		 ---------------------------
+ 
+			   $0000   $0400   $0800   $0C00   $1000   $1400   $1800   $1C00 
+			 +---------------------------------------------------------------+
+			 |                             $8000                             |
+			 +---------------------------------------------------------------+
+ 
+ 
+		 PRG Setup:
+		 ---------------------------
+ 
+			  $8000   $A000   $C000   $E000  
+			 +---------------+---------------+
+			 |     $8000     |     $8000     |
+			 +---------------+---------------+
+		*/
+
+		int prg_reg_16k, chr_reg_8k;
+		int prg_bank_mask_16k;
+		int chr_bank_mask_8k;
+
+		public override bool Configure(NES.EDetectionOrigin origin)
+		{
+			switch (Cart.board_type)
+			{
+				case "MAPPER203":
+					break;
+				default:
+					return false;
+			}
+
+			prg_bank_mask_16k = Cart.prg_size / 16 - 1;
+			chr_bank_mask_8k = Cart.chr_size / 8 - 1;
+
+			return true;
+		}
+
+		public override void SyncState(Serializer ser)
+		{
+			ser.Sync("prg_reg_16k", ref prg_reg_16k);
+			ser.Sync("chr_reg_8k", ref chr_reg_8k);
+			base.SyncState(ser);
+		}
+
+		public override void WritePRG(int addr, byte value)
+		{
+			prg_reg_16k = (value >> 2) & prg_bank_mask_16k;
+			chr_reg_8k = (value & 0x03) & chr_bank_mask_8k;
+		}
+
+		public override byte ReadPRG(int addr)
+		{
+			return ROM[(prg_reg_16k * 0x4000) + (addr & 0x3FFF)];
+		}
+
+		public override byte ReadPPU(int addr)
+		{
+			if (addr < 0x2000)
+			{
+				return VROM[(chr_reg_8k * 0x2000) + addr];
+			}
+			return base.ReadPPU(addr);
+		}
+	}
+}

BizHawk.MultiClient/output/gamedb.txt

@@ -126,6 +126,9 @@ sha1:977286FDC76C34A618E2A2D0270641BC36CFE89C		Nintendo World Championships 1990
 sha1:EC652EE1660E527098102E26A36A8B9B7BB3943F		Castlevania (Konami Collection 2002)	NES		board=NES-UNROM;PRG=128;WRAM=0;VRAM=8;PAD_H=1
 sha1:B5C4E5E858113F5AA5E063BC79A12D7F6B856E6C		Contra (Konami Collection 2002)	NES		board=NES-UNROM;PRG=128;WRAM=0;VRAM=8;PAD_H=1
 
+;multi-cart crap
+sha1:B6D1C372A38D196112AA98905C709AD844BD6627		Super 35-in-1 (6-in-1 VT5201)	NES		board=MAPPER203;PRG=128;CHR=64
+
 ;chinese shit
 sha1:BFA31777E077E64AF0E274B5A22B57C6765D36E1		Fan Kong Jing Ying (Unl) (Ch)	NES		board=MAPPER241;MIR=H
 ;;;;;;;;;;;;;;;;;;;-----------------------------------------------------------------------