GBHawk: make timer <> cpu loop interaction consistent

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

@@ -462,7 +462,7 @@ namespace BizHawk.Emulation.Cores.Components.LR35902
 							break;
 						}
 
-						if (stop_time == (32768 - 2))
+						if (stop_time == (32769))
 						{
 							SpeedFunc(1);
 						}

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

@@ -896,6 +896,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					}
 				}
 			}
+
 			timer_bit_old = Core.double_speed ? Core.timer.divider_reg.Bit(13) : Core.timer.divider_reg.Bit(12);
 
 			if (sequencer_reset_cd > 0)
@@ -904,17 +905,20 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 							
 				if (sequencer_reset_cd == 0)
 				{
+					// seems to be off by one issues here, hard to tell since the write takes place in the cpu loop
+					// but the effect takes place in the sound loop 
 					if (Core.double_speed)
 					{
-						sequencer_len = Core.timer.divider_reg.Bit(13) ? 0 : 1;
+						
-						sequencer_vol = Core.timer.divider_reg.Bit(13) ? 0 : 1;
+						sequencer_len = (Core.timer.divider_reg - 1).Bit(13) ? 0 : 1;
-						sequencer_swp = Core.timer.divider_reg.Bit(13) ? 0 : 1;
+						sequencer_vol = (Core.timer.divider_reg - 1).Bit(13) ? 0 : 1;
+						sequencer_swp = (Core.timer.divider_reg - 1).Bit(13) ? 0 : 1;
 					}
 					else
 					{
-						sequencer_len = Core.timer.divider_reg.Bit(12) ? 0 : 1;
+						sequencer_len = (Core.timer.divider_reg + 1).Bit(12) ? 0 : 1;
-						sequencer_vol = Core.timer.divider_reg.Bit(12) ? 0 : 1;
+						sequencer_vol = (Core.timer.divider_reg + 1).Bit(12) ? 0 : 1;
-						sequencer_swp = Core.timer.divider_reg.Bit(12) ? 0 : 1;
+						sequencer_swp = (Core.timer.divider_reg + 1).Bit(12) ? 0 : 1;
 					}				
 				}
 			}

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

@@ -108,28 +108,34 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					{
 						if (ppu.DMA_start && !cpu.halted && !cpu.stopped) { ppu.DMA_tick(); }
 						serialport.serial_transfer_tick();
-						cpu.ExecuteOne();
 						timer.tick();
+						cpu.ExecuteOne();
+						timer.divider_reg++;
 						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();
+					cpu.ExecuteOne();
+					timer.divider_reg++;
+
 					if (delays_to_process) { process_delays(); }
 				}
 				else
 				{
 					if (double_speed)
 					{
-						cpu.TotalExecutedCycles++;
 						timer.tick();
+						cpu.TotalExecutedCycles++;
+						timer.divider_reg++;
 						if (delays_to_process) { process_delays(); }
 					}
 
-					cpu.TotalExecutedCycles++;
 					timer.tick();
+					cpu.TotalExecutedCycles++;
+					timer.divider_reg++;
+
 					if (delays_to_process) { process_delays(); }
 				}
 
@@ -190,29 +196,37 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 				// These things all tick twice as fast in GBC double speed mode
 				if (ppu.DMA_start && !cpu.halted && !cpu.stopped) { ppu.DMA_tick(); }
 				serialport.serial_transfer_tick();
-				cpu.ExecuteOne();
 				timer.tick();
+				cpu.ExecuteOne();
+				timer.divider_reg++;
+
 				if (delays_to_process) { process_delays(); }
 
 				if (double_speed)
 				{
 					if (ppu.DMA_start && !cpu.halted && !cpu.stopped) { ppu.DMA_tick(); }
 					serialport.serial_transfer_tick();
-					cpu.ExecuteOne();
 					timer.tick();
+					cpu.ExecuteOne();
+					timer.divider_reg++;
+
 					if (delays_to_process) { process_delays(); }
 				}
 			}
 			else
 			{
-				cpu.TotalExecutedCycles++;
 				timer.tick();
+				cpu.TotalExecutedCycles++;
+				timer.divider_reg++;
+
 				if (delays_to_process) { process_delays(); }
 
 				if (double_speed)
 				{
-					cpu.TotalExecutedCycles++;
 					timer.tick();
+					cpu.TotalExecutedCycles++;
+					timer.divider_reg++;
+
 					if (delays_to_process) { process_delays(); }
 				}
 			}
@@ -286,9 +300,6 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 						speed_switch = false;
 						Console.WriteLine("Speed Switch: " + cpu.TotalExecutedCycles);
 
-						// reset the divider (only way for speed_change_timing_fine.gbc and speed_change_cancel.gbc to both work)
-						timer.divider_reg = 0;
-
 						int ret = double_speed ? 32769 : 32769; // actual time needs checking
 						return ret;
 					}
@@ -302,6 +313,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 			}
 			else
 			{
+				// reset the divider (only way for speed_change_timing_fine.gbc and speed_change_cancel.gbc to both work)
+				timer.divider_reg = 1;
 				double_speed = !double_speed;
 				return 0;
 			}
@@ -330,7 +343,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 
 		public void SetIntRegs(byte r)
 		{
-			if (((REG_FF0F & 4) == 4) && ((r & 4) == 0) && is_GBC) { timer.IRQ_block = true; }
+			if (((REG_FF0F & 4) == 4) && ((r & 4) == 0) && timer.IRQ_block && !is_GBC) { r |= 4; }
 			REG_FF0F = r;
 		}
 

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

@@ -56,6 +56,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 			{
 				// DIV register
 				case 0xFF04:
+					// NOTE: even though there is an automatic increment directly after the CPU loop, 
+					// it is still expected that 0 is written here
 					divider_reg = 0;
 					break;
 
@@ -143,7 +145,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 
 		public void tick()
 		{
-			divider_reg++;
+			IRQ_block = false;
 			
 			// pick a bit to test based on the current value of timer control
 			switch (timer_control & 3)
@@ -201,20 +203,16 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					next_free_cycle = 4 + Core.cpu.TotalExecutedCycles;
 
 					// set interrupts
-					if (!IRQ_block)
-					{
 					if (Core.REG_FFFF.Bit(2)) { Core.cpu.FlagI = true; }
 					Core.REG_FF0F |= 0x04;
+					IRQ_block = true;
 				}
 			}
 		}
 
-			IRQ_block = false;
-		}
-
 		public void Reset()
 		{
-			divider_reg = (ushort)(Core.is_GBC ? 0xFFFF : 0x1);
+			divider_reg = (ushort)(Core.is_GBC ?  0xFFFE : 0xFFFE);
 			timer_reload = 0;
 			timer = 0;
 			timer_old = 0;