feat(core): add Machine core state and constructor

src/Chip8.Core/Machine.cs

@@ -0,0 +1,151 @@
+using System;
+
+namespace Chip8.Core;
+
+public sealed partial class Machine
+{
+    public const int displayWidth = 64;
+    public const int displayHeight = 32;
+    public const int displayPixels = displayWidth * displayHeight;
+    public const int memorySize = 4096;
+    public const int xoMemorySize = 65536;
+    public const ushort programStart = 0x200;
+
+    const int registerCount = 16;
+    const int stackDepth = 16;
+    const int keyCount = 16;
+    const ushort fontStart = 0x50;
+    const ushort bigFontStart = 0xA0;
+    const int rplFlagCount = 16;
+    const int audioPatternBytes = 16;
+
+    public byte[] memory { get; }
+    public byte[] v { get; } = new byte[registerCount];
+    public ushort[] stack { get; } = new ushort[stackDepth];
+    public bool[] display { get; } = new bool[displayPixels];
+    public bool[] keypad { get; } = new bool[keyCount];
+
+    public Platform platform { get; }
+    public Video video { get; }
+
+    public byte[] rplFlags { get; } = new byte[rplFlagCount];
+    public byte[] audioPattern { get; } = new byte[audioPatternBytes];
+
+    public ushort i { get; internal set; }
+    public ushort pc { get; internal set; }
+    public byte sp { get; internal set; }
+    public byte delayTimer { get; internal set; }
+    public byte soundTimer { get; internal set; }
+    public int planeMask { get; internal set; }
+    public byte audioPitch { get; internal set; }
+    public bool exited { get; internal set; }
+
+    public bool soundActive => soundTimer > 0;
+    public bool hires => video.hires;
+    public double audioFrequency => 4000.0 * Math.Pow(2.0, (audioPitch - 64) / 48.0);
+
+    public bool drawPending { get; internal set; }
+
+    public bool waitingForKey { get; private set; }
+
+    public Quirks quirks { get; }
+
+    readonly bool[] keypadPrevious = new bool[keyCount];
+    readonly Random rng;
+
+    public Machine(Quirks? quirks = null, int? randomSeed = null, Platform platform = Platform.Chip8)
+    {
+        this.platform = platform;
+        this.quirks = quirks ?? defaultQuirks(platform);
+        memory = new byte[platform == Platform.XoChip ? xoMemorySize : memorySize];
+        video = new Video();
+        rng = randomSeed.HasValue ? new Random(randomSeed.Value) : new Random();
+        reset();
+    }
+
+    static Quirks defaultQuirks(Platform platform) => platform switch
+    {
+        Platform.SuperChip => Quirks.superChip(),
+        Platform.XoChip => Quirks.xoChip(),
+        _ => Quirks.modern(),
+    };
+
+    public void reset()
+    {
+        Array.Clear(memory, 0, memory.Length);
+        Array.Clear(v, 0, v.Length);
+        Array.Clear(stack, 0, stack.Length);
+        Array.Clear(display, 0, display.Length);
+        Array.Clear(keypad, 0, keypad.Length);
+        Array.Clear(keypadPrevious, 0, keypadPrevious.Length);
+        Array.Clear(audioPattern, 0, audioPattern.Length);
+        Array.Copy(FontSet.glyphs, 0, memory, fontStart, FontSet.glyphs.Length);
+        Array.Copy(FontSet.bigGlyphs, 0, memory, bigFontStart, FontSet.bigGlyphs.Length);
+        video.reset();
+        i = 0;
+        pc = programStart;
+        sp = 0;
+        delayTimer = 0;
+        soundTimer = 0;
+        planeMask = 1;
+        audioPitch = 64;
+        exited = false;
+        drawPending = false;
+        waitingForKey = false;
+    }
+
+    public void loadRom(byte[] rom)
+    {
+        int capacity = memory.Length - programStart;
+        if (rom.Length > capacity)
+        {
+            throw new ArgumentException(
+                $"ROM is {rom.Length} bytes, only {capacity} fit above 0x{programStart:X3}.",
+                nameof(rom));
+        }
+
+        reset();
+        Array.Copy(rom, 0, memory, programStart, rom.Length);
+    }
+
+    public void step()
+    {
+        ushort opcode = (ushort)((memory[pc] << 8) | memory[pc + 1]);
+        pc += 2;
+        execute(opcode);
+        Array.Copy(keypad, keypadPrevious, keyCount);
+    }
+
+    public void tickTimers()
+    {
+        if (delayTimer > 0)
+        {
+            delayTimer--;
+        }
+
+        if (soundTimer > 0)
+        {
+            soundTimer--;
+        }
+    }
+
+    public void runFrame(int instructionsPerFrame)
+    {
+        for (int n = 0; n < instructionsPerFrame; n++)
+        {
+            step();
+        }
+
+        tickTimers();
+    }
+
+    public void pressKey(int key)
+    {
+        keypad[key & 0xF] = true;
+    }
+
+    public void releaseKey(int key)
+    {
+        keypad[key & 0xF] = false;
+    }
+}