From bf3d7d228a0a17b905b90a7bd5bff90d33dd2db2 Mon Sep 17 00:00:00 2001
From: Marc Parsons <marc@parsons.cc>
Date: Thu, 30 Apr 2026 17:43:20 +0100
Subject: [PATCH] WIP implementing TZX support

---
 Core/Io/TapManager.cs   | 10 ++++++++
 Core/Io/TzxBlocks.cs    | 24 ++++++++++++++++++
 Core/Io/TzxParser.cs    | 56 +++++++++++++++++++++++++++++++++++++++++
 Core/SpectrumMachine.cs |  3 +++
 Desktop/Form1.cs        |  8 ++++++
 5 files changed, 101 insertions(+)
 create mode 100644 Core/Io/TzxBlocks.cs
 create mode 100644 Core/Io/TzxParser.cs

diff --git a/Core/Io/TapManager.cs b/Core/Io/TapManager.cs
index 64d7c94..87d6ac0 100644
--- a/Core/Io/TapManager.cs
+++ b/Core/Io/TapManager.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using Core.Io;
 
 namespace Core.Io
 {
@@ -7,6 +8,7 @@ namespace Core.Io
     {
         private Queue<byte[]> _blocks = new Queue<byte[]>();
         private byte[] _currentBlock;
+        private List<TzxBlock> _tzxBlocks = new List<TzxBlock>();
 
         // State Machine Tracking
         private enum TapeState { Idle, Pilot, Sync1, Sync2, Data, Pause }
@@ -204,5 +206,13 @@ namespace Core.Io
             _currentBlock = null;
             return _blocks.Count > 0 ? _blocks.Dequeue() : null;
         }
+
+        public void LoadTzxData(List<TzxBlock> blocks)
+        {
+            _tzxBlocks = blocks;
+
+            // Just to prove it works before we build the State Machine!
+            System.Diagnostics.Debug.WriteLine($"Successfully loaded {_tzxBlocks.Count} TZX blocks!");
+        }
     }
 }
\ No newline at end of file
diff --git a/Core/Io/TzxBlocks.cs b/Core/Io/TzxBlocks.cs
new file mode 100644
index 0000000..1fc212c
--- /dev/null
+++ b/Core/Io/TzxBlocks.cs
@@ -0,0 +1,24 @@
+using System;
+
+namespace Core.Io
+{
+    // The base class all future TZX blocks will inherit from
+    public abstract class TzxBlock
+    {
+        public abstract int BlockId { get; }
+    }
+
+    // ID 0x10: Standard Speed Data Block
+    public class StandardSpeedBlock : TzxBlock
+    {
+        public override int BlockId => 0x10;
+
+        // How long to pause the tape in milliseconds after this block loads
+        public ushort PauseAfterMs { get; set; }
+
+        public ushort DataLength { get; set; }
+
+        // The actual tape bytes
+        public byte[] Data { get; set; } = Array.Empty<byte>();
+    }
+}
\ No newline at end of file
diff --git a/Core/Io/TzxParser.cs b/Core/Io/TzxParser.cs
new file mode 100644
index 0000000..659f06f
--- /dev/null
+++ b/Core/Io/TzxParser.cs
@@ -0,0 +1,56 @@
+using Core.Io;
+using System;
+using System.Collections.Generic;
+using System.IO;
+
+namespace Core.Io
+{
+    public class TzxParser
+    {
+        public static List<TzxBlock> Parse(byte[] fileBytes)
+        {
+            List<TzxBlock> blocks = new List<TzxBlock>();
+
+            using (MemoryStream ms = new MemoryStream(fileBytes))
+            using (BinaryReader br = new BinaryReader(ms))
+            {
+                // 1. Verify the 10-Byte Header
+                // Signature is "ZXTape!" followed by EOF (0x1A)
+                byte[] signature = br.ReadBytes(8);
+                string sigString = System.Text.Encoding.ASCII.GetString(signature);
+
+                if (sigString != "ZXTape!\x1A")
+                    throw new Exception("Invalid TZX Signature! Is this a real TZX file?");
+
+                byte majorVersion = br.ReadByte();
+                byte minorVersion = br.ReadByte();
+
+                // 2. Read the blocks until we hit the end of the file
+                while (ms.Position < ms.Length)
+                {
+                    byte blockId = br.ReadByte();
+
+                    switch (blockId)
+                    {
+                        case 0x10: // Standard Speed Data
+                            var stdBlock = new StandardSpeedBlock
+                            {
+                                PauseAfterMs = br.ReadUInt16(),
+                                DataLength = br.ReadUInt16()
+                            };
+                            stdBlock.Data = br.ReadBytes(stdBlock.DataLength);
+                            blocks.Add(stdBlock);
+                            break;
+
+                        // TODO: Add cases for 0x11 (Turbo), 0x12 (Tone), 0x13 (Pulses), etc.
+
+                        default:
+                            throw new NotImplementedException($"TZX Block ID 0x{blockId:X2} is not supported yet!");
+                    }
+                }
+            }
+
+            return blocks;
+        }
+    }
+}
\ No newline at end of file
diff --git a/Core/SpectrumMachine.cs b/Core/SpectrumMachine.cs
index c37c928..f670596 100644
--- a/Core/SpectrumMachine.cs
+++ b/Core/SpectrumMachine.cs
@@ -23,6 +23,7 @@ namespace Core
         public IO_Bus IoBus { get; private set; }
         public ULA Ula { get; private set; }
         public TapManager TapeDeck { get; private set; }
+        public TzxParser _tzxParser { get;  set; }
 
         // Audio (If BeeperDevice is in Desktop, you may need to move it to Core, 
         // or inject it via an interface later. For now, assuming it's accessible).
@@ -276,6 +277,8 @@ namespace Core
             ForceRet();
         }
 
+        
+
         private void ForceRet()
         {
             byte pcLow = Memory.Read(Cpu.SP);
diff --git a/Desktop/Form1.cs b/Desktop/Form1.cs
index c5be012..240ffef 100644
--- a/Desktop/Form1.cs
+++ b/Desktop/Form1.cs
@@ -392,6 +392,14 @@ namespace Desktop
                             {
                                 _machine.LoadSnapshot(fileBytes);
                             }
+                            else if (resourceName.EndsWith(".tzx", StringComparison.OrdinalIgnoreCase))
+                            {
+                                // 1. Pass the raw bytes to our static parser
+                                List<TzxBlock> tzxBlocks = TzxParser.Parse(fileBytes);
+
+                                // 2. Hand the cleanly parsed blocks over to the Tape Deck
+                                _machine.TapeDeck.LoadTzxData(tzxBlocks);
+                            }
                         }
                     }
                 }