Added H Counter to try and fix Sonic demo - didn't work

Core/Io/SmsIoBus.cs

@@ -25,7 +25,11 @@ namespace Core.Io
                 // VDP V-Counter (Vertical Scanline Position)
                 return VideoProcessor.ReadVCounter();
             }
-
+            if (lowerPort == 0x7F)
+            {
+                // THE FIX: VDP H-Counter (Horizontal Pixel Position)
+                return VideoProcessor.ReadHCounter();
+            }
             if (lowerPort >= 0x80 && lowerPort <= 0xBF)
             {
                 // Even ports (like 0xBE) are Data. Odd ports (like 0xBF) are Control.

Core/Video/SmsVdp.cs

@@ -119,6 +119,25 @@ namespace Core.Video
                 return (byte)(_currentScanline - 6);
             }
         }
+        public byte ReadHCounter()
+        {
+            // The Master System H-Counter is a notoriously weird 8-bit timer.
+            // It counts from 0x00 to 0x93, then jumps forward to 0xE9, ending at 0xFF.
+
+            // 1 T-State = 1.5 pixels. The H-Counter increments every 2 pixels.
+            // So H = T * 0.75
+            int h = (int)(_tStateCounter * 0.75);
+
+            if (h <= 0x93)
+            {
+                return (byte)h;
+            }
+            else
+            {
+                // Emulate the hardware jump!
+                return (byte)(h - 0x94 + 0xE9);
+            }
+        }
 
         public void Update(int tStates)
         {