GBHawk: Speed switch timing fix.

src/BizHawk.Emulation.Cores/CPUs/LR35902/Execute.cs

@@ -576,7 +576,7 @@ namespace BizHawk.Emulation.Cores.Components.LR35902
 			// exit halt / stop loop
 			instr_table[256 * 60 * 2 + 60] = IDLE;
 			instr_table[256 * 60 * 2 + 60 + 1] = IDLE;
-			instr_table[256 * 60 * 2 + 60 + 2] = IDLE;
+			instr_table[256 * 60 * 2 + 60 + 2] = HALT_CHK;
 			instr_table[256 * 60 * 2 + 60 + 3] = OP;
 
 			// skipped loop

src/BizHawk.Emulation.Cores/CPUs/LR35902/LR35902.cs

@@ -425,7 +425,7 @@ namespace BizHawk.Emulation.Cores.Components.LR35902
 					if (!stop_check)
 					{
 						// Z contains the second stop byte, not sure if it's useful at all
-						stop_time = SpeedFunc(Regs[Z]);
+						stop_time = SpeedFunc(0);
 						stop_check = true;
 					}
 
@@ -433,6 +433,11 @@ namespace BizHawk.Emulation.Cores.Components.LR35902
 					
 					if (stop_time > 0)
 					{
+						if (stop_time == (32768 - 43))
+						{
+							SpeedFunc(1);							
+						}
+
 						stop_time--;
 
 						if (stop_time == 0)

src/BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawk/GBHawk.IEmulator.cs

@@ -101,10 +101,6 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 				{
 					// These things all tick twice as fast in GBC double speed mode
 					// Note that DMA is halted when the CPU is halted
-					if (ppu.DMA_start && !cpu.halted && !cpu.stopped) { ppu.DMA_tick(); }
-					serialport.serial_transfer_tick();
-					cpu.ExecuteOne();
-					timer.tick();
 
 					if (double_speed)
 					{
@@ -113,17 +109,22 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 						cpu.ExecuteOne();
 						timer.tick();
 					}
+				
+					if (ppu.DMA_start && !cpu.halted && !cpu.stopped) { ppu.DMA_tick(); }
+					serialport.serial_transfer_tick();
+					cpu.ExecuteOne();
+					timer.tick();					
 				}
 				else
 				{
-					cpu.TotalExecutedCycles++;
-					timer.tick();
-
 					if (double_speed)
 					{
 						cpu.TotalExecutedCycles++;
 						timer.tick();
 					}
+
+					cpu.TotalExecutedCycles++;
+					timer.tick();
 				}
 
 				if (in_vblank && !in_vblank_old)
@@ -253,6 +254,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 
 		// Switch Speed (GBC only)
 		public int SpeedFunc(int temp)
+		{
+			if (temp == 0)
 			{
 				if (is_GBC)
 				{
@@ -260,8 +263,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					{
 						speed_switch = false;
 						Console.WriteLine("Speed Switch: " + cpu.TotalExecutedCycles);
-					int ret = double_speed ? (32768 - 20) : (32768 - 20); // actual time needs checking
+						int ret = double_speed ? 32768 - 20 : 32768 - 20; // actual time needs checking
-					double_speed = !double_speed;
 						return ret;
 					}
 
@@ -272,6 +274,12 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 				// if we are in GB mode, return 0, cannot switch speed
 				return 0;
 			}
+			else
+			{
+				double_speed = !double_speed;
+				return 0;
+			}
+		}
 
 		public void GetControllerState(IController controller)
 		{

src/BizHawk.Emulation.Cores/Consoles/Nintendo/GBHawk/HW_Registers.cs

@@ -101,7 +101,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 				case 0xFF4D:
 					if (GBC_compat)
 					{
-						ret = (byte)(((double_speed ? 1 : 0) << 7) + ((speed_switch ? 1 : 0)));
+						ret = (byte)(((double_speed ? 1 : 0) << 7) | (speed_switch ? 1 : 0) | 0x7E);
 					}
 					else
 					{