From 3369dbf43f62a135574764eb4793d665564edd79 Mon Sep 17 00:00:00 2001
From: SaxxonPike <saxxonpike@gmail.com>
Date: Sat, 13 Jul 2019 12:51:39 -0500
Subject: [PATCH] C64: IRQ is implemented as a delay line; no delay added (yet)

---
 .../Computers/Commodore64/MOS/Vic.Registers.cs            | 2 +-
 .../Computers/Commodore64/MOS/Vic.State.cs                | 5 ++---
 BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Vic.cs  | 8 +++++---
 3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Vic.Registers.cs b/BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Vic.Registers.cs
index 98985bc44a..85fa2e8fbc 100644
--- a/BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Vic.Registers.cs
+++ b/BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Vic.Registers.cs
@@ -103,7 +103,7 @@
 							  (_intSpriteDataCollision ? 0x02 : 0x00) |
 							  (_intSpriteCollision ? 0x04 : 0x00) |
 							  (_intLightPen ? 0x08 : 0x00) |
-							  (_pinIrq ? 0x00 : 0x80);
+							  ((_irqBuffer & 1) << 7);
 				case 0x1A:
 					return 0xF0 | (_enableIntRaster ? 0x01 : 0x00) |
 							  (_enableIntSpriteDataCollision ? 0x02 : 0x00) |
diff --git a/BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Vic.State.cs b/BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Vic.State.cs
index 69509feb91..a75f02e3db 100644
--- a/BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Vic.State.cs
+++ b/BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Vic.State.cs
@@ -46,7 +46,6 @@ namespace BizHawk.Emulation.Cores.Computers.Commodore64.MOS
 		private bool _multicolorMode;
 		private bool _pinAec = true;
 		private bool _pinBa = true;
-		private bool _pinIrq = true;
 		private int _pointerCb;
 		private int _pointerVm;
 		private int _rasterInterruptLine;
@@ -85,7 +84,7 @@ namespace BizHawk.Emulation.Cores.Computers.Commodore64.MOS
 		{
 			_pinAec = true;
 			_pinBa = true;
-			_pinIrq = true;
+			_irqBuffer = 0;
 			_ba = true;
 
 			_bufOffset = 0;
@@ -203,7 +202,7 @@ namespace BizHawk.Emulation.Cores.Computers.Commodore64.MOS
 			ser.Sync(nameof(_multicolorMode), ref _multicolorMode);
 			ser.Sync(nameof(_pinAec), ref _pinAec);
 			ser.Sync(nameof(_pinBa), ref _pinBa);
-			ser.Sync(nameof(_pinIrq), ref _pinIrq);
+			ser.Sync(nameof(_irqBuffer), ref _irqBuffer);
 			ser.Sync(nameof(_pointerCb), ref _pointerCb);
 			ser.Sync(nameof(_pointerVm), ref _pointerVm);
 			ser.Sync(nameof(_rasterInterruptLine), ref _rasterInterruptLine);
diff --git a/BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Vic.cs b/BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Vic.cs
index 4c69d69863..85c3230826 100644
--- a/BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Vic.cs
+++ b/BizHawk.Emulation.Cores/Computers/Commodore64/MOS/Vic.cs
@@ -26,7 +26,7 @@ namespace BizHawk.Emulation.Cores.Computers.Commodore64.MOS
 
 		public bool ReadAec() { return _pinAec; }
 		public bool ReadBa() { return _pinBa; }
-		public bool ReadIrq() { return _pinIrq; }
+		public bool ReadIrq() { return (_irqBuffer & 1) != 0; }
 
 		private readonly int _cyclesPerSec;
 		private readonly int[] _rasterXPipeline;
@@ -35,6 +35,7 @@ namespace BizHawk.Emulation.Cores.Computers.Commodore64.MOS
 		private readonly int[] _actPipeline;
 		private readonly int _totalCycles;
 		private readonly int _totalLines;
+		private int _irqBuffer;
 
 		private int _hblankStartCheckXRaster;
 		private int _hblankEndCheckXRaster;
@@ -224,7 +225,6 @@ namespace BizHawk.Emulation.Cores.Computers.Commodore64.MOS
 					_rasterLine = 0;
 					_vcbase = 0;
 					_vc = 0;
-					_badlineEnable = false;
 					_refreshCounter = 0xFF;
 				}
 			}
@@ -340,7 +340,9 @@ namespace BizHawk.Emulation.Cores.Computers.Commodore64.MOS
 				(_enableIntSpriteCollision & _intSpriteCollision) |
 				(_enableIntLightPen & _intLightPen));
 
-			_pinIrq = irqTemp;
+			// IRQ buffer is treated as a delay line
+			_irqBuffer >>= 1;
+			_irqBuffer |= irqTemp ? 0x1 : 0;
 			_pinAec = _ba || _baCount >= 0;
 			_pinBa = _ba;
 		}