NES: pedantic more correct emulation of Fantasy Zone (J). of no interest to anyone.

BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj

@@ -367,6 +367,7 @@
     <Compile Include="Consoles\Nintendo\NES\Boards\SachenSimple.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\SEEPROM.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Sunsoft1.cs" />
+    <Compile Include="Consoles\Nintendo\NES\Boards\Sunsoft1_Alt.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Sunsoft2_m89.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Sunsoft2_m93.cs" />
     <Compile Include="Consoles\Nintendo\NES\Boards\Sunsoft3.cs" />

BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/Sunsoft1_Alt.cs

@@ -0,0 +1,53 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace BizHawk.Emulation.Cores.Nintendo.NES
+{
+	/*
+	 * Fantasy Zone (J, NOT TENGEN)
+	 * It uses its own one-off PCB that rewires the SUNSOFT-1 chip to provide
+	 * PRG control instead of CHR control.  To confuse matters, the game makes
+	 * a second set of compatibility writes to a different set of registers to
+	 * make it run on "Mapper 93" (they were perhaps anticipating putting the
+	 * mask roms on a different board??
+	 * 
+	 * In any event, here is how it's actually emulated.
+	 */
+
+	public sealed class Sunsoft1_Alt : NES.NESBoardBase
+	{
+		int prg;
+
+		public override bool Configure(NES.EDetectionOrigin origin)
+		{
+			if (Cart.board_type != "SUNSOFT-1" || Cart.pcb != "SUNSOFT-4")
+				return false;
+
+			AssertChr(0); AssertVram(8); AssertWram(0); AssertPrg(128);
+			SetMirrorType(Cart.pad_h, Cart.pad_v);
+			return true;
+		}
+
+		public override void WriteWRAM(int addr, byte value)
+		{
+			prg = value & 7;
+		}
+
+		public override byte ReadPRG(int addr)
+		{
+			if (addr >= 0x4000)
+				return ROM[addr & 0x3fff | 7 << 14];
+			else
+				return ROM[addr & 0x3fff | prg << 14];
+		}
+
+		public override void SyncState(BizHawk.Common.Serializer ser)
+		{
+			base.SyncState(ser);
+			ser.Sync("prg", ref prg);
+		}
+
+	}
+}

BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/Sunsoft2_m93.cs

@@ -4,7 +4,6 @@ using BizHawk.Common;
 namespace BizHawk.Emulation.Cores.Nintendo.NES
 {
 	//game=shanghai ; chip=sunsoft-2 ; pcb=SUNSOFT-3R
-	//game=fantasy zone ; chip=sunsoft-1 ; pcb = SUNSOFT-4
 	//this is confusing. see docs/sunsoft.txt
 	public sealed class Sunsoft2_Mapper93 : NES.NESBoardBase
 	{
@@ -23,7 +22,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 					break;
 				case "SUNSOFT-1":
 					if (Cart.pcb != "SUNSOFT-4") return false;
-					break;
+					return false; // this has been moved to Sunsoft1_Alt
 				default:
 					return false;
 			}