GBHawk: controller IRQs enabled by write delayed 4 cycles

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

@@ -14,15 +14,13 @@ namespace BizHawk.Emulation.Cores.Components.LR35902
 						OP };
 		}
 
-		private void INC_16(ushort srcL, ushort srcH)
+		private void INC_16(ushort src_l, ushort src_h)
 		{
 			cur_instr = new[]
 						{IDLE,
 						IDLE,
 						IDLE,
-						INC16,
+						INC16, src_l, src_h,
-						srcL,
-						srcH,
 						IDLE,
 						IDLE,
 						HALT_CHK,
@@ -35,9 +33,7 @@ namespace BizHawk.Emulation.Cores.Components.LR35902
 						{IDLE,
 						IDLE,
 						IDLE,
-						DEC16,
+						DEC16, src_l, src_h,
-						src_l,
-						src_h,
 						IDLE,
 						IDLE,
 						HALT_CHK,

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

@@ -18,6 +18,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 		public bool in_vblank;
 		public bool vblank_rise;
 		public bool controller_was_checked;
+		public bool delays_to_process;
+		public int controller_delay_cd;
 
 		public bool FrameAdvance(IController controller, bool render, bool rendersound)
 		{
@@ -108,12 +110,14 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 						serialport.serial_transfer_tick();
 						cpu.ExecuteOne();
 						timer.tick();
+						if (delays_to_process) { process_delays(); }
 					}
 				
 					if (ppu.DMA_start && !cpu.halted && !cpu.stopped) { ppu.DMA_tick(); }
 					serialport.serial_transfer_tick();
 					cpu.ExecuteOne();
-					timer.tick();					
+					timer.tick();
+					if (delays_to_process) { process_delays(); }
 				}
 				else
 				{
@@ -121,10 +125,12 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					{
 						cpu.TotalExecutedCycles++;
 						timer.tick();
+						if (delays_to_process) { process_delays(); }
 					}
 
 					cpu.TotalExecutedCycles++;
 					timer.tick();
+					if (delays_to_process) { process_delays(); }
 				}
 
 				if (in_vblank && !in_vblank_old)
@@ -186,6 +192,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 				serialport.serial_transfer_tick();
 				cpu.ExecuteOne();
 				timer.tick();
+				if (delays_to_process) { process_delays(); }
 
 				if (double_speed)
 				{
@@ -193,17 +200,20 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					serialport.serial_transfer_tick();
 					cpu.ExecuteOne();
 					timer.tick();
+					if (delays_to_process) { process_delays(); }
 				}
 			}
 			else
 			{
 				cpu.TotalExecutedCycles++;
 				timer.tick();
-				
+				if (delays_to_process) { process_delays(); }
+
 				if (double_speed)
 				{
 					cpu.TotalExecutedCycles++;
-					timer.tick();				
+					timer.tick();
+					if (delays_to_process) { process_delays(); }
 				}
 			}
 
@@ -251,6 +261,18 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 				REG_FF0F |= 0x10;
 			}
 		}
+		
+		public void process_delays()
+		{
+			// triggering an interrupt with a write to the control register takes 4 cycles to trigger interrupt
+			controller_delay_cd--;
+			if (controller_delay_cd == 0)
+			{
+				if (REG_FFFF.Bit(4)) { cpu.FlagI = true; }
+				REG_FF0F |= 0x10;
+				delays_to_process = false;
+			}
+		}
 
 		// Switch Speed (GBC only)
 		public int SpeedFunc(int temp)

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

@@ -38,6 +38,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 			ser.Sync(nameof(controller_was_checked), ref controller_was_checked);
 			ser.Sync(nameof(GB_bios_register), ref GB_bios_register);
 			ser.Sync(nameof(input_register), ref input_register);
+			ser.Sync(nameof(delays_to_process), ref delays_to_process);
+			ser.Sync(nameof(controller_delay_cd), ref controller_delay_cd);
 
 			ser.Sync(nameof(REG_FFFF), ref REG_FFFF);
 			ser.Sync(nameof(REG_FF0F), ref REG_FF0F);

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

@@ -267,13 +267,13 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					}
 					
 					// check for interrupts
+					// if an interrupt is triggered, it is delayed by 4 cycles
 					if (((contr_prev & 8) > 0) && ((input_register & 8) == 0) ||
 						((contr_prev & 4) > 0) && ((input_register & 4) == 0) ||
 						((contr_prev & 2) > 0) && ((input_register & 2) == 0) ||
 						((contr_prev & 1) > 0) && ((input_register & 1) == 0))
 					{
-						if (REG_FFFF.Bit(4)) { cpu.FlagI = true; }
+						controller_delay_cd = 4; delays_to_process = true;
-						REG_FF0F |= 0x10;
 					}
 					
 					break;