GBHAwk: Linked play initial capability

BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawk/SerialPort.cs

@@ -16,6 +16,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 		public int serial_bits;
 		public bool clk_internal;
 		public int clk_rate;
+		public byte going_out;
+		public byte coming_in;
 
 		public byte ReadReg(int addr)
 		{
@@ -84,16 +86,16 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 			if (serial_start)
 			{
 				if (serial_clock > 0) { serial_clock--; }
+
 				if (serial_clock == 0)
 				{
 					if (serial_bits > 0)
 					{
-						send_external_bit((byte)(serial_data & 0x80));
-
 						byte temp = get_external_bit();
 						serial_data = (byte)((serial_data << 1) | temp);
 
 						serial_bits--;
+
 						if (serial_bits == 0)
 						{
 							serial_control &= 0x7F;
@@ -122,12 +124,13 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 		// no device connected returns 0xFF
 		public byte get_external_bit()
 		{
-			return 1;
+			return coming_in;
 		}
 
+		// calling this function buts an external bit on the cable line
 		public void send_external_bit(byte bit_send)
 		{
-
+			going_out = (byte)(bit_send >> 7);
 		}
 
 		public void Reset()
@@ -135,6 +138,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 			serial_control = 0x7E;
 			serial_start = false;
 			serial_data = 0x00;
+			going_out = 0;
+			coming_in = 1;
 		}
 
 		public void SyncState(Serializer ser)
@@ -146,6 +151,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 			ser.Sync("serial_bits", ref serial_bits);
 			ser.Sync("clk_internal", ref clk_internal);
 			ser.Sync("clk_rate", ref clk_rate);
+			ser.Sync("going_out", ref going_out);
+			ser.Sync("coming_in", ref coming_in);
 		}
 	}
 }

BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawkLink/GBHawkLink.IEmulator.cs

@@ -104,6 +104,40 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawkLink
 				L.do_single_step();
 				R.do_single_step();
 
+				// the signal to shift out a bit is when serial_clock = 1
+				if (L.serialport.serial_clock == 1)
+				{
+					if (LinkConnected)
+					{
+						L.serialport.send_external_bit((byte)(L.serialport.serial_data & 0x80));
+
+						if ((R.serialport.clk_rate == -1) && R.serialport.serial_start)
+						{
+							R.serialport.serial_clock = 1;
+							R.serialport.send_external_bit((byte)(R.serialport.serial_data & 0x80));
+							R.serialport.coming_in = L.serialport.going_out;
+						}
+
+						L.serialport.coming_in = R.serialport.going_out;
+					}
+				}
+				else if (R.serialport.serial_clock == 1)
+				{
+					if (LinkConnected)
+					{
+						R.serialport.send_external_bit((byte)(R.serialport.serial_data & 0x80));
+
+						if ((L.serialport.clk_rate == -1) && L.serialport.serial_start)
+						{
+							L.serialport.serial_clock = 1;
+							L.serialport.send_external_bit((byte)(L.serialport.serial_data & 0x80));
+							L.serialport.coming_in = R.serialport.going_out;
+						}
+
+						R.serialport.coming_in = L.serialport.going_out;
+					}
+				}
+
 				// if we hit a frame boundary, update video
 				if (L.vblank_rise)
 				{

BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawkLink/GBHawkLink.IStatable.cs

@@ -57,6 +57,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawkLink
 			ser.Sync("Lag", ref _lagcount);
 			ser.Sync("Frame", ref _frame);
 			ser.Sync("IsLag", ref _islag);
+			ser.Sync("_cableconnected", ref _cableconnected);
+			ser.Sync("_cablediscosignal", ref _cablediscosignal);
 			_controllerDeck.SyncState(ser);
 		}
 	}

BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawkLink/GBHawkLink.cs

@@ -72,6 +72,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawkLink
 			SetupMemoryDomains();
 
 			HardReset();
+
+			LinkConnected = _cableconnected;
 		}
 
 		public void HardReset()