Ammendments to Z80 to make it system agnostic.

Core/Cpu/Z80.cs

@@ -19,7 +19,6 @@ namespace Core.Cpu
             }
         }
 
-        public bool IsZexDocMode { get; set; } = false;
         //T-State counter
         public long TotalTStates { get; set; }
 
@@ -55,19 +54,14 @@ namespace Core.Cpu
         // The Memory Bus
         private readonly IMemory _memory;
         private readonly IO_Bus _simpleIoBus;
-        public TapManager _tapManager;
 
         //External Timing interface
         public Func<ushort, long, int>? WaitStateCallback { get; set; }
 
-        //Misc Variables
+        public Z80(IMemory memory, IO_Bus ioBus)
-        public bool EnableFastLoad { get; set; } = true;
-
-        public Z80(IMemory memory, IO_Bus ioBus, TapManager tapManager)
         {
             _memory = memory;
             _simpleIoBus = ioBus;
-            _tapManager = tapManager;
             Reset();
         }
 
@@ -194,45 +188,6 @@ namespace Core.Cpu
 
         public int Step()
         {           
-            if (IsZexDocMode && PC == 0x0005)
-            {
-                // CP/M System Call Hook
-                if (BC.Low == 2) // C = 2: Print a single character stored in register E
-                {
-                    System.Diagnostics.Debug.Write((char)DE.Low);
-                }
-                else if (BC.Low == 9) // C = 9: Print a string starting at memory address DE, terminated by '$'
-                {
-                    ushort addr = DE.Word;
-                    while (true)
-                    {
-                        char c = (char)ReadMemory(addr++);
-                        if (c == '$') break;
-                        System.Diagnostics.Debug.Write(c);
-                    }
-                }
-
-                // Emulate a 'RET' instruction to return from the CALL 0x0005
-                byte retLow = ReadMemory(SP);
-                SP++;
-                byte retHigh = ReadMemory(SP);
-                SP++;
-                PC = (ushort)((retHigh << 8) | retLow);
-
-                return 10; // Skip normal execution for this cycle
-            }
-            if (PC == 0x0556)
-            {
-                if (EnableFastLoad)
-                {
-                    HandleInstantTapeLoad();
-                    return 100;
-                }
-                else
-                {
-                    _tapManager.Play();
-                }
-            }
 
             // Fetch the next opcode and increment the Program Counter
             byte opcode = ReadMemory(PC++);
@@ -282,54 +237,7 @@ namespace Core.Cpu
             PC = Pop();
         }      
 
-        private void HandleInstantTapeLoad()
-        {
-            // 1. Grab the next block from the virtual cassette
-            byte[] block = _tapManager.GetNextBlock();
-            if (block == null) return; // Tape ended unexpectedly
         
-            // 2. Verify the block type. 
-            // The ROM passes the expected flag (0x00 for Header, 0xFF for Data) in the A register.
-            byte expectedFlag = AF.High;
-            if (block[0] != expectedFlag)
-            {
-                // Tape loading error! Simulate a failure by clearing the Carry flag and returning.
-                AF.Low &= unchecked((byte)~0x01);
-                ExecuteRet();
-                return;
-            }
-
-            // 3. Copy the data block straight into the Spectrum's RAM!
-            // DE holds the number of bytes the ROM *wants*. We copy that much, skipping the Flag byte.
-            int bytesToCopy = DE.Word;
-            for (int i = 0; i < bytesToCopy; i++)
-            {
-                WriteMemory((ushort)(IX.Word + i), block[i + 1]);
-            }
-
-            // 4. Update the registers exactly how the ROM would after a successful load
-            IX.Word = (ushort)(IX.Word + bytesToCopy);
-            DE.Word = 0;
-
-            // 5. Simulate the Checksum Match (Accumulator becomes 0)
-            AF.High = 0x00;
-
-            // 6. Set Carry Flag (Bit 0) for Success, and Zero Flag (Bit 6) for Checksum Match
-            AF.Low |= 0x41; // 0x41 is binary 0100 0001 (Zero and Carry both set)
-
-            // 7. Simulate a standard 'RET' instruction to exit the LD-BYTES routine safely
-            ExecuteRet();
-        }
-
-        // A quick helper to simulate a RET instruction manually
-        private void ExecuteRet()
-        {
-            byte pcLow = ReadMemory(SP);
-            SP++;
-            byte pcHigh = ReadMemory(SP);
-            SP++;
-            PC = (ushort)((pcHigh << 8) | pcLow);
-        }
 
         public string GetFlagsString()
         {

Desktop/Form1.Designer.cs

@@ -43,7 +43,6 @@
             stepToolStripMenuItem = new ToolStripMenuItem();
             resetToolStripMenuItem1 = new ToolStripMenuItem();
             optionsToolStripMenuItem = new ToolStripMenuItem();
-            fastLoadingToolStripMenuItem = new ToolStripMenuItem();
             HighSpeedToolStripMenuItem = new ToolStripMenuItem();
             ((System.ComponentModel.ISupportInitialize)picScreen).BeginInit();
             menuStrip1.SuspendLayout();
@@ -156,20 +155,11 @@
             // 
             // optionsToolStripMenuItem
             // 
-            optionsToolStripMenuItem.DropDownItems.AddRange(new ToolStripItem[] { fastLoadingToolStripMenuItem, HighSpeedToolStripMenuItem });
+            optionsToolStripMenuItem.DropDownItems.AddRange(new ToolStripItem[] { HighSpeedToolStripMenuItem });
             optionsToolStripMenuItem.Name = "optionsToolStripMenuItem";
             optionsToolStripMenuItem.Size = new Size(75, 24);
             optionsToolStripMenuItem.Text = "Options";
             // 
-            // fastLoadingToolStripMenuItem
-            // 
-            fastLoadingToolStripMenuItem.Checked = true;
-            fastLoadingToolStripMenuItem.CheckState = CheckState.Checked;
-            fastLoadingToolStripMenuItem.Name = "fastLoadingToolStripMenuItem";
-            fastLoadingToolStripMenuItem.Size = new Size(224, 26);
-            fastLoadingToolStripMenuItem.Text = "Fast TAP Loading";
-            fastLoadingToolStripMenuItem.Click += fastLoadingToolStripMenuItem_Click;
-            // 
             // HighSpeedToolStripMenuItem
             // 
             HighSpeedToolStripMenuItem.Name = "HighSpeedToolStripMenuItem";
@@ -212,7 +202,6 @@
         private ToolStripMenuItem stepToolStripMenuItem;
         private ToolStripMenuItem resetToolStripMenuItem1;
         private ToolStripMenuItem optionsToolStripMenuItem;
-        private ToolStripMenuItem fastLoadingToolStripMenuItem;
         private ToolStripMenuItem HighSpeedToolStripMenuItem;
     }
 }

Desktop/Form1.cs

@@ -50,7 +50,7 @@ namespace Desktop
                 _memoryBus.CrapRAMData();
                 byte[] romData = RomLoader.Load("48.rom");
                 _memoryBus.LoadRom(romData);
-                _cpu = new Z80(_memoryBus, _simpleIoBus, _tapManager);
+                _cpu = new Z80(_memoryBus, _simpleIoBus);
                 _cpu.WaitStateCallback = _ula.GetContentionDelay;
 
             }
@@ -112,6 +112,13 @@ namespace Desktop
 
                         long tStatesBefore = _cpu.TotalTStates;
 
+                        // --- HARDWARE INTERCEPTS ---
+                        if (_cpu.PC == 0x0556 && _tapManager.HasBlocks)
+                        {
+                                HandleInstantTapeLoad();
+                                _cpu.TotalTStates += 100; // Charge some arbitrary time for the fast load
+                        }
+
                         // --- Execute Instruction ---
                         _cpu.Step();
 
@@ -218,6 +225,52 @@ namespace Desktop
             });
         }
 
+        private void HandleInstantTapeLoad()
+        {
+            byte[] block = _tapManager.GetNextBlock(); // Your original Queue.Dequeue() method
+            if (block == null) return;
+
+            byte expectedFlag = _cpu.AF.High;
+            if (block[0] != expectedFlag)
+            {
+                // Block mismatch (e.g. found data when looking for a header)
+                // Clear the carry flag to simulate a tape loading error
+                _cpu.AF.Low &= unchecked((byte)~0x01);
+                ForceRet();
+                return;
+            }
+
+            int bytesToCopy = _cpu.DE.Word;
+
+            // Safety check just in case the TAP file is malformed
+            int actualBytes = Math.Min(bytesToCopy, block.Length - 1);
+
+            // Directly inject the payload into the RAM
+            for (int i = 0; i < actualBytes; i++)
+            {
+                _memoryBus.Write((ushort)(_cpu.IX.Word + i), block[i + 1]);
+            }
+
+            // --- Update Registers to match a PERFECT ROM Load ---
+            _cpu.IX.Word = (ushort)(_cpu.IX.Word + actualBytes);
+            _cpu.DE.Word = (ushort)(bytesToCopy - actualBytes); // Should hit 0
+            _cpu.HL.Word = 0x0000; // The ROM zeroes this out after calculating checksums
+
+            // Checksum Zero (A = 0x00), Success Flag / Zero Flag Set (F = 0x41)
+            _cpu.AF.Word = 0x0041;
+
+            ForceRet();
+        }
+
+        private void ForceRet()
+        {
+            // Pop the return address off the stack just like a real RET instruction
+            byte pcLow = _memoryBus.Read(_cpu.SP);
+            _cpu.SP++;
+            byte pcHigh = _memoryBus.Read(_cpu.SP);
+            _cpu.SP++;
+            _cpu.PC = (ushort)((pcHigh << 8) | pcLow);
+        }
         
 
         private void UpdateScreenBitmap()
@@ -246,21 +299,14 @@ namespace Desktop
                 if (ofd.ShowDialog() == DialogResult.OK)
                 {
                     byte[] tapBytes = File.ReadAllBytes(ofd.FileName);
-                    _cpu._tapManager.LoadTapData(tapBytes);
+                    _tapManager.LoadTapData(tapBytes);
                     tapeLoaded = true;
                 }
             }
             _isPaused = false;
         }
 
-        private void fastLoadingToolStripMenuItem_Click(object sender, EventArgs e)
-        {
-            // Toggle the checkmark UI
-            fastLoadingToolStripMenuItem.Checked = !fastLoadingToolStripMenuItem.Checked;
         
-            // Tell the CPU to enable or disable the ROM hijack
-            _cpu.EnableFastLoad = fastLoadingToolStripMenuItem.Checked;
-        }
         private void openSNAToolStripMenuItem_Click(object sender, EventArgs e)
         {
             _isPaused = true;