The InputCallbackSystem on this Core is now fully operational. https://www.youtube.com/watch?v=g7-tskP0OzI

BizHawk.Emulation.Cores/Consoles/Nintendo/SNES9X/LibSnes9x.cs

@@ -25,6 +25,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.SNES9X
 			public int vheight;
 			public IntPtr sptr;
 			public int slen;
+			public int padread;
 		};
 
 		public enum LeftPortDevice : uint
@@ -43,6 +44,9 @@ namespace BizHawk.Emulation.Cores.Nintendo.SNES9X
 			Justifier = 5
 		}
 
+		[UnmanagedFunctionPointer(CC)]
+		public delegate void InputCallback();
+
 		const CallingConvention CC = CallingConvention.Cdecl;
 
 		[BizImport(CC)]
@@ -67,5 +71,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.SNES9X
 		public abstract void biz_get_memory_area(int which, [In, Out] memory_area mem);
 		[BizImport(CC)]
 		public abstract void biz_post_load_state();
+		[BizImport(CC)]
+		public abstract void biz_set_input_callback(InputCallback callback);
 	}
 }

BizHawk.Emulation.Cores/Consoles/Nintendo/SNES9X/Snes9x.cs

@@ -16,7 +16,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.SNES9X
 	[ServiceNotApplicable(typeof(IDriveLight))]
 	public class Snes9x : IEmulator, IVideoProvider, ISoundProvider, IStatable,
 		ISettable<Snes9x.Settings, Snes9x.SyncSettings>,
-		ISaveRam
+		ISaveRam, IInputPollable
 	{
 		private LibSnes9x _core;
 		private PeRunner _exe;
@@ -71,6 +71,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.SNES9X
 			PutSettings(settings);
 			InitMemoryDomains();
 			InitSaveram();
+
+			_inputCallback = InputCallbacks.Call;
 		}
 
 		#region controller
@@ -301,6 +303,8 @@ namespace BizHawk.Emulation.Cores.Nintendo.SNES9X
 
 		public void FrameAdvance(IController controller, bool render, bool rendersound = true)
 		{
+			_core.biz_set_input_callback(InputCallbacks.Count > 0 ? _inputCallback : null);
+
 			if (controller.IsPressed("Power"))
 				_core.biz_hard_reset();
 			else if (controller.IsPressed("Reset"))
@@ -311,6 +315,9 @@ namespace BizHawk.Emulation.Cores.Nintendo.SNES9X
 			LibSnes9x.frame_info frame = new LibSnes9x.frame_info();
 
 			_core.biz_run(frame, _inputState);
+			IsLagFrame = frame.padread == 0;
+			if (IsLagFrame)
+				LagCount++;
 			using (_exe.EnterExit())
 			{
 				Blit(frame);
@@ -444,9 +451,12 @@ namespace BizHawk.Emulation.Cores.Nintendo.SNES9X
 
 		#endregion
 
-		// TODO
-		public int LagCount { get; private set; }
-		public bool IsLagFrame { get; private set; }
+		private LibSnes9x.InputCallback _inputCallback;
+
+		public int LagCount { get; set; }
+		public bool IsLagFrame { get; set; }
+
+		public IInputCallbackSystem InputCallbacks { get; } = new InputCallbackSystem();
 
 		#region IStatable
 
@@ -479,6 +489,7 @@ namespace BizHawk.Emulation.Cores.Nintendo.SNES9X
 			LagCount = reader.ReadInt32();
 			IsLagFrame = reader.ReadBoolean();
 			// any managed pointers that we sent to the core need to be resent now!
+			_core.biz_set_input_callback(null);
 
 			_core.biz_post_load_state();
 		}

waterbox/snes9x

@@ -1 +1 @@
-Subproject commit 431f7453b322661b60d9bae20a8730bb9399f847
+Subproject commit 69b89b25c7e2d0c97412a27081d21a0834137319