From defdfa6e2ed41e34a04cc94e6005a421badfe019 Mon Sep 17 00:00:00 2001
From: adelikat <adelikat@tasvideos.org>
Date: Tue, 25 Aug 2015 20:11:32 -0400
Subject: [PATCH] NESHawk - fix mapper 164

---
 .../Consoles/Nintendo/NES/Boards/Mapper164.cs | 38 +++++++++++--------
 1 file changed, 22 insertions(+), 16 deletions(-)

diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/Mapper164.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/Mapper164.cs
index 5d0dbc9647..ed6f380762 100644
--- a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/Mapper164.cs
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/Mapper164.cs
@@ -6,8 +6,10 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 	{
 		// http://wiki.nesdev.com/w/index.php/INES_Mapper_164
 
-		int prg_bank;
-		int prg_bank_mask_32k;
+		private int _prgHigh;
+		private int _prgLow;
+
+		private int prg_bank_mask_32k;
 
 		public override bool Configure(NES.EDetectionOrigin origin)
 		{
@@ -18,7 +20,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 				default:
 					return false;
 			}
-			prg_bank = 0xFF;
+
+			_prgLow = 0xFF;
 			prg_bank_mask_32k = Cart.prg_size / 32 - 1;
 			SetMirrorType(Cart.pad_h, Cart.pad_v);
 			return true;
@@ -26,32 +29,35 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 
 		public override void WriteEXP(int addr, byte value)
 		{
-			addr = (addr + 0x4000) & 0xF300;
-			if (addr == 0x5000 || addr == 0xD000)
-				prg_bank = value;
-		}
-
-		public override void WritePRG(int addr, byte value)
-		{
-			addr = (addr + 0x8000) & 0xF300;
-			if (addr == 0x5000 || addr == 0xD000)
-				prg_bank = value;
+			addr = (addr + 0x4000) & 0x7300;
+			switch (addr)
+			{
+				case 0x5000:
+					_prgLow = value;
+					break;
+				case 0x5100:
+					_prgHigh = value;
+					break;
+			}
 		}
 
 		public override byte ReadPRG(int addr)
 		{
-			return ROM[addr + ((prg_bank & prg_bank_mask_32k) * 0x8000)];
+			int bank = (_prgHigh << 4) | (_prgLow & 0xF);
+			bank &= prg_bank_mask_32k;
+			return ROM[(bank * 0x8000) + (addr & 0x7FFF)];
 		}
 
 		public override void SyncState(Serializer ser)
 		{
 			base.SyncState(ser);
-			ser.Sync("prg", ref prg_bank);
+			ser.Sync("prgHigh", ref _prgHigh);
+			ser.Sync("prgLow", ref _prgLow);
 		}
 
 		public override void NESSoftReset()
 		{
-			prg_bank = 0xFF;
+			_prgHigh = 0xFF;
 			base.NESSoftReset();
 		}
 	}