From 5b5932696d6e151d00c1d02c63e197f63a6f7b10 Mon Sep 17 00:00:00 2001
From: pjgat09 <pjgat09@gmail.com>
Date: Wed, 21 Mar 2012 01:02:24 +0000
Subject: [PATCH] M6532: Added a dedicated cycle count variable to fix a timer
 issue. TIA: Increment the M6532 cycle count when in wsync.

---
 .../Consoles/Atari/2600/Atari2600.Core.cs         |  1 +
 BizHawk.Emulation/Consoles/Atari/2600/M6532.cs    | 15 ++++++++++-----
 BizHawk.Emulation/Consoles/Atari/2600/TIA.cs      |  8 ++++++++
 3 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/BizHawk.Emulation/Consoles/Atari/2600/Atari2600.Core.cs b/BizHawk.Emulation/Consoles/Atari/2600/Atari2600.Core.cs
index 1745ecb744..188f2ba90c 100644
--- a/BizHawk.Emulation/Consoles/Atari/2600/Atari2600.Core.cs
+++ b/BizHawk.Emulation/Consoles/Atari/2600/Atari2600.Core.cs
@@ -142,6 +142,7 @@ namespace BizHawk
 				tia.execute(1);
 				tia.execute(1);
 
+				m6532.tick();
 				cpu.Execute(1);
 				if (cpu.PendingCycles <= 0)
 				{
diff --git a/BizHawk.Emulation/Consoles/Atari/2600/M6532.cs b/BizHawk.Emulation/Consoles/Atari/2600/M6532.cs
index c32c2354f0..5bd2e432d0 100644
--- a/BizHawk.Emulation/Consoles/Atari/2600/M6532.cs
+++ b/BizHawk.Emulation/Consoles/Atari/2600/M6532.cs
@@ -22,7 +22,7 @@ namespace BizHawk.Emulation.Consoles.Atari
 		public byte swchb = 0x0B;
 
 		public bool resetOccured = false;
-
+		public int totalCycles = 0;
 
 		public M6532(MOS6507 cpu, byte[] ram, Atari2600 core)
 		{
@@ -35,6 +35,11 @@ namespace BizHawk.Emulation.Consoles.Atari
 
 		}
 
+		public void tick()
+		{
+			totalCycles++;
+		}
+
 		public byte ReadMemory(ushort addr)
 		{
 			ushort maskedAddr;
@@ -53,12 +58,12 @@ namespace BizHawk.Emulation.Consoles.Atari
 					Console.WriteLine("6532 timer read: " + maskedAddr.ToString("x"));
 
 					// Calculate the current value on the timer
-					int timerCurrentValue = timerFinishedCycles - Cpu.TotalExecutedCycles;
+					int timerCurrentValue = timerFinishedCycles - totalCycles;
 
 					interruptTriggered = false;
 
 					// If the timer has not finished, shift the value down for the game
-					if (Cpu.TotalExecutedCycles < timerFinishedCycles)
+					if (totalCycles < timerFinishedCycles)
 					{
 						return (byte)(((timerCurrentValue) >> timerShift) & 0xFF);
 					}
@@ -93,7 +98,7 @@ namespace BizHawk.Emulation.Consoles.Atari
 					}
 					else if (maskedAddr == 0x05) // interrupt
 					{
-						if ((timerFinishedCycles - Cpu.TotalExecutedCycles >= 0)|| (interruptEnabled && interruptTriggered))
+						if ((timerFinishedCycles - totalCycles >= 0)|| (interruptEnabled && interruptTriggered))
 						{
 							return 0x00;
 						}
@@ -130,7 +135,7 @@ namespace BizHawk.Emulation.Consoles.Atari
 					timerStartValue = value << timerShift;
 
 					// Calculate when the timer will be finished
-					timerFinishedCycles = timerStartValue + Cpu.TotalExecutedCycles;
+					timerFinishedCycles = timerStartValue + totalCycles;
 
 					Console.WriteLine("6532 timer write:  " + maskedAddr.ToString("x"));
 
diff --git a/BizHawk.Emulation/Consoles/Atari/2600/TIA.cs b/BizHawk.Emulation/Consoles/Atari/2600/TIA.cs
index a0aa5c5f39..1734436f7d 100644
--- a/BizHawk.Emulation/Consoles/Atari/2600/TIA.cs
+++ b/BizHawk.Emulation/Consoles/Atari/2600/TIA.cs
@@ -719,9 +719,17 @@ namespace BizHawk.Emulation.Consoles.Atari
 			}
 			else if (maskedAddr == 0x02) // WSYNC
 			{
+				int count = 0;
 				while (hsyncCnt > 0)
 				{
+					count++;
 					execute(1);
+
+					// Add a cycle to the cpu every 3 TIA clocks (corrects timer error in M6532)
+					if (count % 3 == 0)
+					{
+						core.m6532.tick();
+					}
 				}
 			}
 			else if (maskedAddr == 0x04) // NUSIZ0