commodore64: implement proper lag frame counting

BizHawk.Emulation/BizHawk.Emulation.csproj

@@ -100,6 +100,7 @@
     <Compile Include="Computers\Commodore64\SidSoundProvider.cs" />
     <Compile Include="Computers\Commodore64\SidWaveformCalculator.cs" />
     <Compile Include="Computers\Commodore64\SidWaveformGenerator.cs" />
+    <Compile Include="Computers\Commodore64\Timing.cs" />
     <Compile Include="Computers\Commodore64\Via.cs" />
     <Compile Include="Computers\Commodore64\VicIINew.cs" />
     <Compile Include="Computers\Commodore64\VicIINewPipeline.cs" />

BizHawk.Emulation/Computers/Commodore64/C64.cs

@@ -91,11 +91,13 @@ namespace BizHawk.Emulation.Computers.Commodore64
 		// process frame
 		public void FrameAdvance(bool render, bool rendersound)
 		{
-			_frame++;
-			_islag = true;
-
 			int cyclesPerFrame = vic.CyclesPerFrame;
+			
+			// bizhawk interface setup
+			_frame++;
+			mem.inputWasRead = false;
 
+			// apply any media if needed
 			foreach (IMedia media in mediaAttached)
 			{
 				if (!media.Loaded() && media.Ready())
@@ -104,8 +106,10 @@ namespace BizHawk.Emulation.Computers.Commodore64
 				}
 			}
 
+			// refresh the input values
 			PollInput();
 
+			// perform the cycle
 			for (int i = 0; i < cyclesPerFrame; i++)
 			{
 				vic.PerformCycle();
@@ -124,6 +128,8 @@ namespace BizHawk.Emulation.Computers.Commodore64
 				}
 			}
 
+			_islag = !mem.inputWasRead;
+
 			if (_islag)
 			{
 				LagCount++;

BizHawk.Emulation/Computers/Commodore64/MemBus.cs

@@ -62,6 +62,7 @@ namespace BizHawk.Emulation.Computers.Commodore64
 
 		// registers
 		public byte busData;
+		public bool inputWasRead;
 		public bool readTrigger = true;
 		public bool writeTrigger = true;
 
@@ -364,6 +365,8 @@ namespace BizHawk.Emulation.Computers.Commodore64
 						result = ReadColorRam(addr);
 						break;
 					case MemoryDesignation.Cia0:
+						if ((addr & 0xF) < 0x02)
+							inputWasRead = true;
 						result = cia0.Read(addr);
 						break;
 					case MemoryDesignation.Cia1:

BizHawk.Emulation/Computers/Commodore64/Timing.cs

@@ -0,0 +1,40 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace BizHawk.Emulation.Computers.Commodore64
+{
+	public class Timing
+	{
+		public int crystalFreq;
+		public uint timer;
+
+		public Timing(Region timingRegion)
+		{
+			switch (timingRegion)
+			{
+				case Region.NTSC:
+					crystalFreq = 14318181;
+					break;
+				case Region.PAL:
+					crystalFreq = 17734472;
+					break;
+			}
+		}
+
+		public void Advance()
+		{
+			// need an unchecked block here since the timer will wrap
+			unchecked
+			{
+				timer++;
+			}
+		}
+
+		public bool IsCycle(int divisor)
+		{
+			return (timer % divisor) == 0;
+		}
+	}
+}