GBHawk: Speed change and window fixes

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

@@ -603,7 +603,7 @@ namespace BizHawk.Emulation.Cores.Components.LR35902
 			// Stop loop
 			instr_table[256 * 60 * 2 + 60 * 5] = IDLE;
 			instr_table[256 * 60 * 2 + 60 * 5 + 1] = IDLE;
-			instr_table[256 * 60 * 2 + 60 * 5 + 2] = IDLE;
+			instr_table[256 * 60 * 2 + 60 * 5 + 2] = HALT_CHK;
 			instr_table[256 * 60 * 2 + 60 * 5 + 3] = STOP;
 
 			// interrupt vectors

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

@@ -430,12 +430,41 @@ namespace BizHawk.Emulation.Cores.Components.LR35902
 					}
 
 					interrupt_src_reg = GetIntRegs(0);
-					
+
 					if (stop_time > 0)
 					{
-						if (stop_time == (32768 - 43))
+						// Timer interrupts can prematurely terminate a speedchange, nt sure about other sources
+						// NOTE: some testing around the edge case of where the speed actually changes is needed						
+						if (I_use && interrupts_enabled)
 						{
-							SpeedFunc(1);							
+							interrupts_enabled = false;
+							I_use = false;
+
+							TraceCallback?.Invoke(new TraceInfo
+							{
+								Disassembly = "====un-stop====",
+								RegisterInfo = ""
+							});
+
+							stopped = false;
+							stop_check = false;
+							stop_time = 0;
+
+							TraceCallback?.Invoke(new TraceInfo
+							{
+								Disassembly = "====IRQ====",
+								RegisterInfo = ""
+							});
+
+							// call interrupt processor 
+							// lowest bit set is highest priority
+							instr_pntr = 256 * 60 * 2 + 60 * 6; // point to Interrupt
+							break;
+						}
+
+						if (stop_time == (32768 - 2))
+						{
+							SpeedFunc(1);
 						}
 
 						stop_time--;
@@ -454,16 +483,22 @@ namespace BizHawk.Emulation.Cores.Components.LR35902
 							instr_pntr = 256 * 60 * 2 + 60;
 
 							stop_check = false;
+
+							break;
 						}
-						else
+
+						// If a button is pressed during speed change, the processor will jam
+						if (interrupt_src_reg.Bit(4))
 						{
-							instr_pntr = 256 * 60 * 2 + 60 * 5; // point to stop loop
+							stop_time++;
+							break;
 						}
 					}
-					else if (interrupt_src_reg.Bit(4)) // button pressed, even if interrupts are not enabled, still exists stop
+					
+					// Button press will exit stop loop even if speed change in progress, even without interrupts enabled
+					if (interrupt_src_reg.Bit(4))
 					{
 						// TODO: On a gameboy, you can only un-STOP once, needs further testing
-						
 						TraceCallback?.Invoke(new TraceInfo
 						{
 							Disassembly = "====un-stop====",

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

@@ -790,7 +790,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 				total_counter = 0;
 
 				// TODO: If Window is turned on midscanline what happens? When is this check done exactly?
-				if ((window_started && window_latch) || (window_is_reset && !window_latch && (LY >= window_y_latch)))
+				if ((window_started && window_latch) || (window_is_reset && !window_latch && (LY > window_y_latch)))
 				{
 					window_y_tile_inc++;
 					if (window_y_tile_inc==8)
@@ -973,7 +973,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					pixel_counter++;
 
 					if (pixel_counter == 160)
-					{
+					{						
 						read_case = 8;
 						hbl_countdown = 2;
 					}

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

@@ -788,7 +788,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 				total_counter = 0;
 
 				// TODO: If Window is turned on midscanline what happens? When is this check done exactly?
-				if ((window_started && window_latch) || (window_is_reset && !window_latch && (LY >= window_y_latch)))
+				if ((window_started && window_latch) || (window_is_reset && !window_latch && (LY > window_y_latch)))
 				{
 					window_y_tile_inc++;
 					if (window_y_tile_inc==8)

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

@@ -285,7 +285,11 @@ 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
+
+						// 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;
 					}
 

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

@@ -7,6 +7,8 @@ using BizHawk.Emulation.Cores.Components.LR35902;
 using BizHawk.Emulation.Cores.Consoles.Nintendo.Gameboy;
 using System.Runtime.InteropServices;
 
+// TODO: mode1_disableint_gbc.gbc behaves differently between GBC and GBA, why?
+
 namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 {
 	[Core(

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

@@ -48,7 +48,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					{
 						// don't draw for one frame after turning on
 						blank_frame = true;
-					}
+					}				
 					LCDC = value;
 					break; 
 				case 0xFF41: // STAT
@@ -481,7 +481,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 				total_counter = 0;
 
 				// TODO: If Window is turned on midscanline what happens? When is this check done exactly?
-				if ((window_started && window_latch) || (window_is_reset && !window_latch && (LY >= window_y_latch)))
+				if ((window_started && window_latch) || (window_is_reset && !window_latch && (LY > window_y_latch)))
 				{
 					window_y_tile_inc++;
 					if (window_y_tile_inc==8)

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

@@ -68,6 +68,9 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 				case 0xFF07:
 					timer_control = (byte)((timer_control & 0xf8) | (value & 0x7)); // only bottom 3 bits function
 
+					// NOTE: On GBA models, there is a race condition when enabling with a change in bit check
+					// that would result in a state change that is not consistent in all models, see tac_set_disabled.gbc
+
 					// NOTE: On GBA only, there is a glitch where if the current timer control is 7 and the written value is 7 and
 					// there is a coincident timer increment, there will be an additional increment along with this write.
 					// not sure it effects all models or of exact details, see test tac_set_timer_disabled.gbc