diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/MMC3_family/Mapper215.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/MMC3_family/Mapper215.cs
index 29b7c88258..83bdafa7fd 100644
--- a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/MMC3_family/Mapper215.cs
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/MMC3_family/Mapper215.cs
@@ -78,14 +78,14 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 		{
 			base.SyncState(ser);
 			ser.Sync("exRegs", ref exRegs);
-			ser.Sync("cmd", ref is_mk3);
+			ser.Sync("is_mk3", ref is_mk3);
+			ser.Sync("ptg_regs_8k", ref prg_regs_8k);
 			ser.Sync("prg_mask", ref prg_mask_8k);
 			ser.Sync("chr_mask", ref chr_mask_1k);
 		}
 
 		public void sync_prg(int i)
 		{
-
 			if ((exRegs[0] & 0x80) == 0)
 			{
 				int temp = 0;
@@ -101,8 +101,6 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 					prg_regs_8k[i] = (byte)(temp & prg_mask_8k);
 				//}
 			}
-
-
 		}
 
 		public void sync_prg_2()
@@ -117,7 +115,6 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 				prg_regs_8k[1] = (byte)(bank+1);
 				prg_regs_8k[2] = (byte)bank;
 				prg_regs_8k[3] = (byte)(bank+1);
-
 			}
 			else
 			{
@@ -126,7 +123,6 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 				sync_prg(2);
 				sync_prg(3);
 			}
-
 		}
 
 		public override void WriteEXP(int addr, byte value)
diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/MMC3_family/Mapper217.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/MMC3_family/Mapper217.cs
index 9839ddddea..e142867282 100644
--- a/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/MMC3_family/Mapper217.cs
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/NES/Boards/MMC3_family/Mapper217.cs
@@ -3,11 +3,15 @@ using BizHawk.Common.NumberExtensions;
 
 namespace BizHawk.Emulation.Cores.Nintendo.NES
 {
-	// TODO
 	public sealed class Mapper217 : MMC3Board_Base
 	{
 		private ByteBuffer exRegs = new ByteBuffer(4);
 
+		public ByteBuffer prg_regs_8k = new ByteBuffer(4);
+		private int prg_mask_8k, chr_mask_1k;
+		private byte[] regs_sec = { 0, 6, 3, 7, 5, 2, 4, 1 };
+
+
 		public override bool Configure(NES.EDetectionOrigin origin)
 		{
 			switch (Cart.board_type)
@@ -25,6 +29,14 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 			exRegs[2] = 0x03;
 			exRegs[3] = 0x00;
 
+			prg_mask_8k = Cart.prg_size / 8 - 1;
+			chr_mask_1k = Cart.chr_size - 1;
+
+			prg_regs_8k[0] = 0;
+			prg_regs_8k[1] = 1;
+			prg_regs_8k[2] = (byte)(0xFE & prg_mask_8k);
+			prg_regs_8k[3] = (byte)(0xFF & prg_mask_8k);
+
 			return true;
 		}
 
@@ -32,6 +44,26 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 		{
 			base.SyncState(ser);
 			ser.Sync("exRegs", ref exRegs);
+			ser.Sync("ptg_regs_8k", ref prg_regs_8k);
+			ser.Sync("prg_mask", ref prg_mask_8k);
+			ser.Sync("chr_mask", ref chr_mask_1k);
+		}
+
+		public void sync_prg()
+		{
+			int temp = 0;
+			for (int i=0;i<4;i++)
+			{
+			temp = mmc3.prg_regs_8k[i];
+
+			if ((exRegs[1] & 0x8) > 0)
+				temp = temp & 0x1F;
+			else
+				temp = ((temp & 0x0F) | (exRegs[1] & 0x10));
+
+				temp |= (exRegs[1] << 5 & 0x60);
+			prg_regs_8k[i] = (byte)(temp & prg_mask_8k);
+			}
 		}
 
 		public override void WriteEXP(int addr, byte value)
@@ -39,12 +71,28 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 			if (addr == 0x1000)
 			{
 				exRegs[0] = value;
-				// TODO: if value & 0x80, prg 16k mode
+				if ((value & 0x80)>0)
+				{
+					int bank = (byte)((value & 0x0F) | (exRegs[1] << 4 & 0x30));
+
+					bank *= 2;
+					bank &= prg_mask_8k;
+
+					prg_regs_8k[0] = (byte)bank;
+					prg_regs_8k[1] = (byte)(bank + 1);
+					prg_regs_8k[2] = (byte)bank;
+					prg_regs_8k[3] = (byte)(bank + 1);
+				}
+				else
+				{
+					sync_prg();
+				}
 			}
 
 			else if (addr == 0x1001)
 			{
 				exRegs[1] = value;
+				sync_prg();
 			}
 
 			else if (addr == 0x1007)
@@ -55,16 +103,103 @@ namespace BizHawk.Emulation.Cores.Nintendo.NES
 			base.WriteEXP(addr, value);
 		}
 
-		protected override int Get_PRGBank_8K(int addr)
-		{
-			if (exRegs[1].Bit(3))
-			{
-				return base.Get_PRGBank_8K(addr) & 0x1F;
-			}
-			else
-			{
-				return base.Get_PRGBank_8K(addr) & 0x1F | (exRegs[1] & 0x10);
-			}
+		public override void WritePRG(int addr, byte value)
+		{
+			switch ((addr + 0x8000) & 0xE001)
+			{
+				case 0x8000:
+					if (exRegs[2] > 0)
+					{
+						base.WritePRG(0x4000, value);
+					}
+					else
+					{
+						base.WritePRG(0x0000, value);
+						sync_prg();
+					}
+					break;
+				case 0x8001:
+					if (exRegs[2] > 0)
+					{
+						value = (byte)((value & 0xC0) | regs_sec[value & 0x07]);
+						exRegs[3] = 1;
+
+						base.WritePRG(0x0000, value);
+						sync_prg();
+					}
+					else
+					{
+						base.WritePRG(0x0001, value);
+						sync_prg();
+					}
+					break;
+				case 0xA000:
+					if (exRegs[2] > 0)
+					{
+						if ((exRegs[3] > 0) && ((exRegs[0] & 0x80) == 0 || (mmc3.reg_addr & 0x7) < 6))
+						{
+							exRegs[3] = 0;
+							base.WritePRG(0x0001, value);
+							sync_prg();
+						}
+					}
+					else
+					{
+						if (value == 0)
+						{
+							SetMirrorType(EMirrorType.Vertical);
+						}
+						else
+						{
+							SetMirrorType(EMirrorType.Horizontal);
+						}
+					}
+					break;
+				case 0xA001:
+					if (exRegs[2] > 0)
+					{
+						if (value == 0)
+						{
+							SetMirrorType(EMirrorType.Vertical);
+						}
+						else
+						{
+							SetMirrorType(EMirrorType.Horizontal);
+						}
+					} else
+					{
+						base.WritePRG(0x2001, value);
+					}
+					break;
+			}
+
+			if (addr>=0x4000) 
+				base.WritePRG(addr, value);
+		}
+
+		public override byte ReadPPU(int addr)
+		{
+			if (addr < 0x2000)
+			{
+				int bank_1k = base.Get_CHRBank_1K(addr);
+
+				if ((exRegs[1] & 0x8) == 0)
+					bank_1k = (bank_1k & 0x7F) | (exRegs[1] << 3 & 0x80);
+
+				bank_1k |= (exRegs[1] << 8 & 0x300);
+				bank_1k &= chr_mask_1k;
+				addr = (bank_1k << 10) | (addr & 0x3FF);
+				return VROM[addr];
+			}
+			else return base.ReadPPU(addr);
+		}
+
+
+		public override byte ReadPRG(int addr)
+		{
+			int bank = addr >> 13;
+			bank = prg_regs_8k[bank];
+			return ROM[(bank << 13) + (addr & 0x1FFF)];
 		}
 	}
 }