Apple II - wire up the lag counter, may or may not be correct logic, don't know too much about Apple II internals, but eyeballing the code, it looks like a reasonable place to decide if input was polled.

BizHawk.Emulation.Cores/BizHawk.Emulation.Cores.csproj

@@ -122,6 +122,9 @@
     <Compile Include="Computers\AppleII\AppleII.IEmulator.cs">
       <DependentUpon>AppleII.cs</DependentUpon>
     </Compile>
+    <Compile Include="Computers\AppleII\AppleII.IInputPollable.cs">
+        <DependentUpon>AppleII.cs</DependentUpon>
+    </Compile>
     <Compile Include="Computers\AppleII\AppleII.IMemoryDomains.cs">
       <DependentUpon>AppleII.cs</DependentUpon>
     </Compile>

BizHawk.Emulation.Cores/Computers/AppleII/AppleII.IEmulator.cs

@@ -34,7 +34,6 @@ namespace BizHawk.Emulation.Cores.Computers.AppleII
 
 		public IController Controller { get; set; }
 
-
 		public int Frame { get; set; }
 
 		public string SystemId { get { return "AppleII"; } }
@@ -51,6 +50,8 @@ namespace BizHawk.Emulation.Cores.Computers.AppleII
 		public void ResetCounters()
 		{
 			Frame = 0;
+			LagCount = 0;
+			IsLagFrame = false;
 		}
 
 		public CoreComm CoreComm { get; private set; }

BizHawk.Emulation.Cores/Computers/AppleII/AppleII.IStatable.cs

@@ -22,6 +22,8 @@ namespace BizHawk.Emulation.Cores.Computers.AppleII
 		public void SaveStateBinary(BinaryWriter writer)
 		{
 			writer.Write(Frame);
+			writer.Write(LagCount);
+			writer.Write(IsLagFrame);
 			writer.Write(CurrentDisk);
 			_machine.SaveState(writer);
 		}
@@ -29,6 +31,8 @@ namespace BizHawk.Emulation.Cores.Computers.AppleII
 		public void LoadStateBinary(BinaryReader reader)
 		{
 			Frame = reader.ReadInt32();
+			LagCount = reader.ReadInt32();
+			IsLagFrame = reader.ReadBoolean();
 			CurrentDisk = reader.ReadInt32();
 			InitDisk();
 			_machine.LoadState(reader);

BizHawk.Emulation.Cores/Computers/AppleII/AppleII.cs

@@ -172,6 +172,11 @@ namespace BizHawk.Emulation.Cores.Computers.AppleII
 			
 			_machine.Buttons = GetButtons();
 			_machine.BizFrameAdvance();
+			if (IsLagFrame)
+			{
+				LagCount++;
+			}
+
 			Frame++;
 		}
 

ExternalCoreProjects/Virtu/Machine.cs

@@ -327,6 +327,7 @@ namespace Jellyfish.Virtu
 
 				public void BizFrameAdvance()
 				{
+					Lagged = true;
 					Services.GetService<KeyboardService>().Update();
                     Services.GetService<GamePortService>().Update();
 					//frame begins at vsync.. beginning of vblank
@@ -384,5 +385,7 @@ namespace Jellyfish.Virtu
 
         private AutoResetEvent _pauseEvent = new AutoResetEvent(false);
         private AutoResetEvent _unpauseEvent = new AutoResetEvent(false);
+
+		public bool Lagged { get; set; }
     }
 }

ExternalCoreProjects/Virtu/Memory.cs

@@ -286,6 +286,7 @@ namespace Jellyfish.Virtu
         [SuppressMessage("Microsoft.Maintainability", "CA1505:AvoidUnmaintainableCode")]
         private int ReadIoRegionC0C0(int address)
         {
+			Machine.Lagged = false;
 			switch (address)
             {
             case 0xC000: case 0xC001: case 0xC002: case 0xC003: case 0xC004: case 0xC005: case 0xC006: case 0xC007: // [7-15]