Add Z80 CPU skeleton, RegisterPair struct, and MemoryBus implementation

Core/Cpu/RegisterPair.cs

@@ -0,0 +1,17 @@
+using System.Runtime.InteropServices;
+
+namespace Core.Cpu
+{
+    [StructLayout(LayoutKind.Explicit)]
+    public struct RegisterPair
+    {
+        [FieldOffset(0)]
+        public ushort Word;
+
+        [FieldOffset(0)]
+        public byte Low;
+
+        [FieldOffset(1)]
+        public byte High;
+    }
+}

Core/Cpu/Z80.cs

@@ -0,0 +1,74 @@
+using System;
+using Core.Interfaces;
+
+namespace Core.Cpu
+{
+    public partial class Z80
+    {
+        // Main Register Set
+        public RegisterPair AF;
+        public RegisterPair BC;
+        public RegisterPair DE;
+        public RegisterPair HL;
+
+        // Alternate Register Set
+        public RegisterPair AF_Prime;
+        public RegisterPair BC_Prime;
+        public RegisterPair DE_Prime;
+        public RegisterPair HL_Prime;
+
+        // Index Registers
+        public RegisterPair IX;
+        public RegisterPair IY;
+
+        // Special Purpose Registers
+        public ushort PC; // Program Counter
+        public ushort SP; // Stack Pointer
+        public byte I;    // Interrupt Vector
+        public byte R;    // Memory Refresh
+
+        // The Memory Bus
+        private readonly IMemory _memory;
+
+        public Z80(IMemory memory)
+        {
+            _memory = memory;
+            Reset();
+        }
+
+        public void Reset()
+        {
+            PC = 0x0000;
+            // The Z80 initializes SP to 0xFFFF on boot
+            SP = 0xFFFF;
+
+            AF.Word = 0;
+            BC.Word = 0;
+            DE.Word = 0;
+            HL.Word = 0;
+        }
+
+        public int Step()
+        {
+            // Fetch the next opcode and increment the Program Counter
+            byte opcode = _memory.Read(PC++);
+
+            // Decode and execute
+            return ExecuteOpcode(opcode);
+        }
+
+        private int ExecuteOpcode(byte opcode)
+        {
+            switch (opcode)
+            {
+                case 0x00: // NOP (No Operation)
+                    return 4; // Takes 4 T-states
+
+                // We will expand this massive list soon!
+
+                default:
+                    throw new NotImplementedException($"Opcode 0x{opcode:X2} at PC 0x{(PC - 1):X4} is not implemented.");
+            }
+        }
+    }
+}

Core/Interfaces/IMemory.cs

@@ -0,0 +1,8 @@
+namespace Core.Interfaces
+{
+    public interface IMemory
+    {
+        byte Read(ushort address);
+        void Write(ushort address, byte value);
+    }
+}

Core/Memory/MemoryBus.cs

@@ -0,0 +1,47 @@
+using System;
+using Core.Interfaces;
+
+namespace Core.Memory
+{
+    public class MemoryBus : IMemory
+    {
+        // The flat 64KB memory space
+        private readonly byte[] _memory = new byte[0x10000];
+
+        public byte Read(ushort address)
+        {
+            return _memory[address];
+        }
+
+        public void Write(ushort address, byte value)
+        {
+            /* ZX Spectrum 48K Memory Map:
+             * 0x0000 - 0x3FFF: ROM (16KB) -> Cannot write here!
+             * 0x4000 - 0x57FF: Display File (Screen Pixels)
+             * 0x5800 - 0x5AFF: Color Attributes
+             * 0x5B00 - 0xFFFF: General Purpose RAM
+             */
+
+            if (address < 0x4000)
+            {
+                // Attempted to write to the ROM area. 
+                // We simply ignore the write command, just like real hardware.
+                return;
+            }
+
+            _memory[address] = value;
+        }
+
+        // Helper method to load the original Sinclair ROM file
+        public void LoadRom(byte[] romData)
+        {
+            if (romData.Length > 0x4000)
+            {
+                throw new ArgumentException("ROM file exceeds the 16KB capacity of Bank 0.");
+            }
+
+            // Copy the ROM data into the very beginning of the memory array
+            Array.Copy(romData, 0, _memory, 0, romData.Length);
+        }
+    }
+}

Desktop/Desktop.csproj

@@ -8,4 +8,8 @@
     <ImplicitUsings>enable</ImplicitUsings>
   </PropertyGroup>
 
+  <ItemGroup>
+    <ProjectReference Include="..\Core\Core.csproj" />
+  </ItemGroup>
+
 </Project>

Desktop/Form1.Designer.cs

@@ -28,10 +28,17 @@
         /// </summary>
         private void InitializeComponent()
         {
-            this.components = new System.ComponentModel.Container();
+            SuspendLayout();
-            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
+            // 
-            this.ClientSize = new System.Drawing.Size(800, 450);
+            // Form1
-            this.Text = "Form1";
+            // 
+            AutoScaleDimensions = new SizeF(8F, 20F);
+            AutoScaleMode = AutoScaleMode.Font;
+            ClientSize = new Size(800, 450);
+            Name = "Form1";
+            Text = "Form1";
+            Load += Form1_Load;
+            ResumeLayout(false);
         }
 
         #endregion

Desktop/Form1.cs

@@ -6,5 +6,10 @@ namespace Desktop
         {
             InitializeComponent();
         }
+
+        private void Form1_Load(object sender, EventArgs e)
+        {
+
+        }
     }
 }

ZxSpectrumEmulation.sln

@@ -3,7 +3,25 @@ Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio Version 17
 VisualStudioVersion = 17.14.36811.4 d17.14
 MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Core", "Core\Core.csproj", "{0706292A-3AD4-4A04-A3CE-B692AC69D7A4}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Desktop", "Desktop\Desktop.csproj", "{57408F14-0EEC-4E9E-BC97-3764DEB5738D}"
+EndProject
 Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{0706292A-3AD4-4A04-A3CE-B692AC69D7A4}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{0706292A-3AD4-4A04-A3CE-B692AC69D7A4}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{0706292A-3AD4-4A04-A3CE-B692AC69D7A4}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{0706292A-3AD4-4A04-A3CE-B692AC69D7A4}.Release|Any CPU.Build.0 = Release|Any CPU
+		{57408F14-0EEC-4E9E-BC97-3764DEB5738D}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{57408F14-0EEC-4E9E-BC97-3764DEB5738D}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{57408F14-0EEC-4E9E-BC97-3764DEB5738D}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{57408F14-0EEC-4E9E-BC97-3764DEB5738D}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
 	EndGlobalSection