GBHawk: mode 1 overhaul, fixes several bugs

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

@@ -147,7 +147,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					STAT = (byte)((value & 0xF8) | (STAT & 7) | 0x80);
 
 					if (((STAT & 3) == 0) && STAT.Bit(3) && !glitch_state) { HBL_INT = true; } else { HBL_INT = false; }
-					if (((STAT & 3) == 1) && STAT.Bit(4)) { VBL_INT = true; } else { VBL_INT = false; }
+					//if (((STAT & 3) == 1) && STAT.Bit(4)) { VBL_INT = true; } else if ((STAT & 3) == 1) { VBL_INT = false; }
 					// OAM not triggered?
 					// if (((STAT & 3) == 2) && STAT.Bit(5)) { OAM_INT = true; } else { OAM_INT = false; }
 
@@ -533,6 +533,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					if (LY == 0 && LY_inc == 0)
 					{
 						LY_inc = 1;
+						in_vbl = false;
 						Core.in_vblank = false;
 
 						//STAT &= 0xFC;
@@ -556,6 +557,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 
 					if (LY == 144)
 					{
+						in_vbl = true;
 						Core.in_vblank = true;
 					}
 				}
@@ -564,6 +566,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 				if (LCD_was_off)
 				{
 					//VBL_INT = false;
+					in_vbl = false;
 					Core.in_vblank = false;
 					LCD_was_off = false;
 
@@ -579,31 +582,51 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					cycle = 8;
 				}
 
-				// the VBL stat is continuously asserted
+				// NOTE: timing differences between when ios is one (GBC mode) and off do not occur in the bios code so are not 
-				if (LY >= 144)
+				// represented here, see the GBC PPU for more details.
+				if (in_vbl)
 				{
-					if (STAT.Bit(4))
+					if (cycle == 4)
 					{
-						if ((cycle >= 5) && (LY == 144))
+						// Timing note: LYC interrupt cannot block mode 1 stat by itself
+						// But, the glitchy mode 2 stat check combined with LYC does block it. So adjust old stat line here
+						stat_line_old = VBL_INT | HBL_INT | OAM_INT;
+
+						if (LY == 144) { HBL_INT = false; }
+						
+					}
+
+					// glitchy check of mode 2
+					if (LY == 144)
+					{
+						if (cycle <= 4)
 						{
-							VBL_INT = true;
+							if (!STAT.Bit(5)) { VBL_INT = false; }
+							if ((cycle == 4) && !STAT.Bit(4)) { VBL_INT = false; }
 						}
-						else if (LY > 144)
+
+						if ((cycle >= 2) && (cycle < 4))
 						{
-							VBL_INT = true;
+							// there is an edge case where a VBL INT is triggered if STAT bit 5 is set
+							if (STAT.Bit(5)) { VBL_INT = true; }
 						}
 					}
 
-					if ((cycle == 2) && (LY == 144))
+					// mode 1 starts here, is asserted continuously
+					if (STAT.Bit(4))
 					{
-						// there is an edge case where a VBL INT is triggered if STAT bit 5 is set
+						if (LY == 144)
-						if (STAT.Bit(5)) { VBL_INT = true; }
+						{
+							if (cycle >= 4) { VBL_INT = true; }
+						}
+						else
+						{
+							VBL_INT = true;
+						}
 					}
 
 					if ((cycle == 4) && (LY == 144))
 					{
-						HBL_INT = false;
-
 						// set STAT mode to 1 (VBlank) and interrupt flag if it is enabled
 						STAT &= 0xFC;
 						STAT |= 0x01;
@@ -612,11 +635,6 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 						Core.REG_FF0F |= 0x01;
 					}
 
-					if ((cycle == 4) && (LY == 144))
-					{
-						if (STAT.Bit(5)) { VBL_INT = false; }
-					}
-
 					if ((cycle == 8) && (LY == 153))
 					{
 						LY = 0;
@@ -624,8 +642,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 						Core.cpu.LY = LY;
 					}
 				}
-
+				else
-				if (!Core.in_vblank)
 				{
 					if (no_scan)
 					{
@@ -689,25 +706,31 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					{
 						if (cycle < 83)
 						{
-							if (cycle == 2)
+							if (cycle <= 4)
 							{
-								if (LY != 0)
+								if ((cycle == 2) && (LY != 0))
 								{
 									HBL_INT = false;
 
 									if (STAT.Bit(5)) { OAM_INT = true; }
 								}
-							}
-							else if (cycle == 4)
-							{
-								// here mode 2 will be set to true and interrupts fired if enabled
-								STAT &= 0xFC;
-								STAT |= 0x2;
 
-								if (LY == 0)
+								// the last few cycles of mode 1 still trigger mode 1 int
+								if (cycle < 4)
 								{
-									VBL_INT = false;
+									if (STAT.Bit(4) && ((STAT & 3) == 1)) { VBL_INT = true; }
-									if (STAT.Bit(5)) { OAM_INT = true; }
+								}
+								else
+								{
+									// here mode 2 will be set to true and interrupts fired if enabled
+									STAT &= 0xFC;
+									STAT |= 0x2;
+
+									if (LY == 0)
+									{
+										VBL_INT = false;
+										if (STAT.Bit(5)) { OAM_INT = true; }
+									}
 								}
 							}
 
@@ -799,6 +822,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 
 				VBL_INT = LYC_INT = HBL_INT = OAM_INT = false;
 
+				in_vbl = true;
 				Core.in_vblank = true;
 
 				LCD_was_off = true;
@@ -1849,7 +1873,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 			scroll_y = 0;
 			scroll_x = 0;
 			LY = 0;
-			LYC = 0;
+			LYC = 0xFF;
 			LY_read = 0;
 			DMA_addr = 0;
 			BGP = 0xFF;
@@ -1920,6 +1944,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 			pal_change_blocked = false;
 
 			glitch_state = false;
+			in_vbl = true;
 		}
 	}
 }

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

@@ -142,10 +142,11 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					break; 
 				case 0xFF41: // STAT
 					// note that their is no stat interrupt bug in GBC
+					Console.WriteLine("stat " + " " + STAT + " " + value + " " + LY + " " + cycle + " " + Core.REG_FF0F);
 					STAT = (byte)((value & 0xF8) | (STAT & 7) | 0x80);
 
 					if (((STAT & 3) == 0) && STAT.Bit(3) && !glitch_state) { HBL_INT = true; } else { HBL_INT = false; }
-					if (((STAT & 3) == 1) && STAT.Bit(4)) { VBL_INT = true; } else { VBL_INT = false; }
+					//if (((STAT & 3) == 1) && STAT.Bit(4)) { VBL_INT = true; } else if ((STAT & 3) == 1) { VBL_INT = false; }
 					// OAM not triggered?
 					// if (((STAT & 3) == 2) && STAT.Bit(5)) { OAM_INT = true; } else { OAM_INT = false; }
 
@@ -532,6 +533,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					if (LY == 0 && LY_inc == 0)
 					{
 						LY_inc = 1;
+						in_vbl = false;
 						Core.in_vblank = false;
 
 						//STAT &= 0xFC;
@@ -556,6 +558,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 
 					if (LY == 144)
 					{
+						in_vbl = true;
 						Core.in_vblank = true;
 					}
 				}
@@ -564,6 +567,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 				if (LCD_was_off)
 				{
 					//VBL_INT = false;
+					in_vbl = false;
 					Core.in_vblank = false;
 					LCD_was_off = false;
 
@@ -582,31 +586,49 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					//cycle = 8;
 				}
 
-				// the VBL stat is continuously asserted
+				if (in_vbl)
-				if (LY >= 144)
 				{
-					if (STAT.Bit(4))
+					if (cycle == 4)
 					{
-						if ((cycle >= (3 + 1 * LYC_offset)) && (LY == 144))
+						// Timing note: LYC interrupt cannot block mode 1 stat by itself
+						// But, the glitchy mode 2 stat check combined with LYC does block it. So adjust old stat line here
+						stat_line_old = VBL_INT | HBL_INT | OAM_INT;
+
+						if (LY == 144) { HBL_INT = false; }
+
+					}
+
+					// glitchy check of mode 2
+					if (LY == 144)
+					{
+						if (cycle <= 4)
 						{
-							VBL_INT = true;
+							if (!STAT.Bit(5)) { VBL_INT = false; }
+							if ((cycle == 4) && !STAT.Bit(4)) { VBL_INT = false; }
 						}
-						else if (LY > 144)
+
+						if ((cycle >= 2) && (cycle < 4))
 						{
-							VBL_INT = true;
+							// there is an edge case where a VBL INT is triggered if STAT bit 5 is set
+							if (STAT.Bit(5)) { VBL_INT = true; }
 						}
 					}
 
-					if ((cycle == 2) && (LY == 144))
+					// mode 1 starts here, is asserted continuously
+					if (STAT.Bit(4))
 					{
-						// there is an edge case where a VBL INT is triggered if STAT bit 5 is set
+						if (LY == 144)
-						if (STAT.Bit(5)) { VBL_INT = true; }
+						{
+							if (cycle >= 4) { VBL_INT = true; }
+						}
+						else
+						{
+							VBL_INT = true;
+						}
 					}
 
 					if ((cycle == 4) && (LY == 144))
 					{
-						HBL_INT = false;
-
 						// set STAT mode to 1 (VBlank) and interrupt flag if it is enabled
 						STAT &= 0xFC;
 						STAT |= 0x01;
@@ -615,11 +637,6 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 						Core.REG_FF0F |= 0x01;
 					}
 
-					if ((cycle == 4) && (LY == 144))
-					{
-						if (STAT.Bit(5)) { VBL_INT = false; }
-					}
-
 					if ((cycle == 8) && (LY == 153))
 					{
 						LY = 0;
@@ -627,8 +644,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 						Core.cpu.LY = LY;
 					}
 				}
-
+				else
-				if (!Core.in_vblank)
 				{
 					if (no_scan)
 					{
@@ -693,25 +709,31 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					{
 						if (cycle < 83)
 						{
-							if (cycle == 2)
+							if (cycle <= 4)
 							{
-								if (LY != 0)
+								if ((cycle == 2) && (LY != 0))
 								{
 									HBL_INT = false;
 									
 									if (STAT.Bit(5)) { OAM_INT = true; }
 								}
-							}
-							else if (cycle == 4)
-							{
-								// here mode 2 will be set to true and interrupts fired if enabled
-								STAT &= 0xFC;
-								STAT |= 0x2;
 
-								if (LY == 0)
+								// the last few cycles of mode 1 still trigger mode 1 int
+								if (cycle < 4)
 								{
-									VBL_INT = false;
+									if (STAT.Bit(4) && ((STAT & 3) == 1)) { VBL_INT = true; }
-									if (STAT.Bit(5)) { OAM_INT = true; }
+								}
+								else
+								{
+									// here mode 2 will be set to true and interrupts fired if enabled
+									STAT &= 0xFC;
+									STAT |= 0x2;
+
+									if (LY == 0)
+									{
+										VBL_INT = false;
+										if (STAT.Bit(5)) { OAM_INT = true; }
+									}
 								}
 							}
 
@@ -804,6 +826,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 
 				VBL_INT = LYC_INT = HBL_INT = OAM_INT = false;
 
+				in_vbl = true;
 				Core.in_vblank = true;
 
 				LCD_was_off = true;
@@ -1794,7 +1817,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 			scroll_y = 0;
 			scroll_x = 0;
 			LY = 0;
-			LYC = 0;
+			LYC = 0xFF;
 			LY_read = 0;
 			DMA_addr = 0;
 			BGP = 0xFF;
@@ -1865,6 +1888,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 			LYC_offset = 2;
 
 			glitch_state = false;
+			in_vbl = true;
 
 			LY_153_change = 10;
 		}

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

@@ -162,6 +162,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					if (LY == 0 && LY_inc == 0)
 					{
 						LY_inc = 1;
+						in_vbl = false;
 						Core.in_vblank = false;
 
 						STAT &= 0xFC;
@@ -183,6 +184,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 
 					if (LY == 144)
 					{
+						in_vbl = true;
 						Core.in_vblank = true;
 					}
 				}
@@ -191,6 +193,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 				if (LCD_was_off)
 				{
 					//VBL_INT = false;
+					in_vbl = false;
 					Core.in_vblank = false;
 					LCD_was_off = false;
 
@@ -206,22 +209,31 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					cycle = 8;
 				}
 
+				// Timing note: LYC=143 does not by itself block mode1 stat int. But, the glitchy mode 2 stat check combined with 
+				// LYC=143 does block it
+
 				// the VBL stat is continuously asserted
-				if (LY >= 144)
+				if (in_vbl)
 				{
+					if ((cycle <= 4) && (LY == 144))
+					{
+						if (!STAT.Bit(5)) { VBL_INT = false; }
+						if ((cycle == 4) && !STAT.Bit(4)) { VBL_INT = false; }
+					}
+
 					if (STAT.Bit(4))
 					{
-						if ((cycle >= 4) && (LY == 144))
+						if (LY == 144)
 						{
-							VBL_INT = true;
+							if (cycle >= 4) { VBL_INT = true; }
 						}
-						else if (LY > 144)
+						else
 						{
 							VBL_INT = true;
 						}
 					}
 
-					if ((cycle == 2) && (LY == 144))
+					if ((cycle >= 2) && (cycle < 4) && (LY == 144))
 					{
 						// there is an edge case where a VBL INT is triggered if STAT bit 5 is set
 						if (STAT.Bit(5)) { VBL_INT = true; }
@@ -239,11 +251,6 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 						Core.REG_FF0F |= 0x01;
 					}
 
-					if ((cycle == 4) && (LY == 144))
-					{
-						if (STAT.Bit(5)) { VBL_INT = false; }
-					}
-
 					if ((cycle == 6) && (LY == 153))
 					{
 						LY = 0;
@@ -251,8 +258,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 						Core.cpu.LY = LY;
 					}
 				}
-
+				else
-				if (!Core.in_vblank)
 				{
 					if (no_scan)
 					{
@@ -315,27 +321,34 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 					{
 						if (cycle < 83)
 						{
-							if (cycle == 2)
+							if (cycle <= 4)
 							{
-								if (LY != 0)
+								if ((cycle == 2) && (LY != 0))
 								{
 									HBL_INT = false;
+
 									if (STAT.Bit(5)) { OAM_INT = true; }
 								}
-							}
-							else if (cycle == 4)
-							{
-								// apparently, writes can make it to OAM one cycle longer then reads
-								OAM_access_write = false;
 
-								// here mode 2 will be set to true and interrupts fired if enabled
+								// the last few cycles of mode 1 still trigger mode 1 int
-								STAT &= 0xFC;
+								if (cycle < 4)
-								STAT |= 0x2;
-
-								if (LY == 0)
 								{
-									VBL_INT = false;
+									if (STAT.Bit(4) && ((STAT & 3) == 1)) { VBL_INT = true; }
-									if (STAT.Bit(5)) { OAM_INT = true; }
+								}
+								else
+								{
+									// apparently, writes can make it to OAM one cycle longer then reads
+									OAM_access_write = false;
+
+									// here mode 2 will be set to true and interrupts fired if enabled
+									STAT &= 0xFC;
+									STAT |= 0x2;
+
+									if (LY == 0)
+									{
+										VBL_INT = false;
+										if (STAT.Bit(5)) { OAM_INT = true; }
+									}
 								}
 							}
 
@@ -415,6 +428,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 
 				VBL_INT = LYC_INT = HBL_INT = OAM_INT = false;
 
+				in_vbl = true;
 				Core.in_vblank = true;			
 
 				LCD_was_off = true;
@@ -1242,7 +1256,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 			scroll_y = 0;
 			scroll_x = 0;
 			LY = 0;
-			LYC = 0;
+			LYC = 0xFF;
 			DMA_addr = 0xFF;
 			BGP = 0xFF;
 			obj_pal_0 = 0xFF;
@@ -1278,6 +1292,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 			window_y_tile_inc = 0;
 
 			glitch_state = false;
+			in_vbl = true;
 		}
 	}
 }

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

@@ -118,6 +118,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 		public int LYC_offset; // in double speed mode it appears timing changes for LYC int
 		public bool glitch_state; // writing to STAT to enable HBL interrupt won't trigger it if the ppu just turned on
 		public int LY_153_change; // the timing of LYC chaning to 153 looks like it varies with speed mode
+		public bool in_vbl; // writes to turn on mode 2 stat interrupts can trigger vbl stat at the start of vbl
 
 		// variables not in state
 		public int total_counter;
@@ -286,6 +287,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.GBHawk
 			ser.Sync(nameof(LYC_offset), ref LYC_offset);
 			ser.Sync(nameof(glitch_state), ref glitch_state);
 			ser.Sync(nameof(LY_153_change), ref LY_153_change);
+			ser.Sync(nameof(in_vbl), ref in_vbl);
 		}
 	}
 }