Initial Commit

.gitignore

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+# Zig Build Directories
+/zig-cache
+/zig-out
+
+
+# ROM directory
+/bin
+

build.zig

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+const Builder = @import("std").build.Builder;
+
+pub fn build(b: *Builder) void {
+    // Standard target options allows the person running `zig build` to choose
+    // what target to build for. Here we do not override the defaults, which
+    // means any target is allowed, and the default is native. Other options
+    // for restricting supported target set are available.
+    const target = b.standardTargetOptions(.{});
+
+    // Standard release options allow the person running `zig build` to select
+    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall.
+    const mode = b.standardReleaseOptions();
+
+    const exe = b.addExecutable("zig8", "src/main.zig");
+    exe.setTarget(target);
+    exe.setBuildMode(mode);
+    exe.linkSystemLibrary("SDL2");
+    exe.linkSystemLibrary("c");
+    exe.install();
+
+    const run_cmd = exe.run();
+    run_cmd.step.dependOn(b.getInstallStep());
+    if (b.args) |args| {
+        run_cmd.addArgs(args);
+    }
+
+    const run_step = b.step("run", "Run the app");
+    run_step.dependOn(&run_cmd.step);
+}

src/cpu.zig

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+const std = @import("std");
+const expect = @import("std").testing.expect;
+const panic = @import("std").debug.panic;
+const Dir = @import("std").fs.Dir;
+const Instruction = @import("instructions.zig").Instruction;
+const InstrType = @import("instructions.zig").Type;
+const draw_sprite = @import("display.zig").draw_sprite;
+const Display = @import("display.zig").Display;
+const Point = @import("display.zig").Point;
+
+pub const Cpu = struct {
+    i: u16,
+    pc: u16,
+    sp: u16,
+    v: [16]u8,
+    stack: [16]u16,
+    memory: [0x1000]u8,
+    disp: Display,
+};
+
+
+pub fn fetch(cpu: *Cpu) u16 {
+    const high: u16 = cpu.memory[cpu.pc];
+    const low: u16 = cpu.memory[cpu.pc + 1];
+    
+    cpu.pc += 2;
+
+    return high << 8 | low;
+}
+
+pub fn decode(cpu: *Cpu, word: u16) ?Instruction {
+    const nib1: u4 = @intCast(u4, (word & 0xF000) >> 12);
+    const nib2: u4 = @intCast(u4, (word & 0x0F00) >> 8);
+    const nib3: u4 = @intCast(u4, (word & 0x00F0) >> 4);
+    const nib4: u4 = @intCast(u4, (word & 0x000F) >> 0);
+
+
+    if (nib1 == 0x0) {
+        // nib2 is 0x0, nib3 is 0xE
+
+        if (nib4 == 0) {
+            // 0x00E0 | CLS
+            return Instruction.CLS; 
+        }
+
+        if (nib4 == 0xE) {
+            // 0x00EE | RET
+            return Instruction.RET;
+        }
+    } else if (nib1 == 0x1) {
+        // 0x1nnn | JP addr
+
+        const addr = calc_u12(nib2, nib3, nib4);
+        return Instruction { .JP = addr };
+    } else if (nib1 == 0x2) {
+        // 0x2nnn | CALL addr
+
+        const addr = calc_u12(nib2, nib3, nib4);
+        return Instruction { .CALL = addr };
+    } else if (nib1 == 0x3) {
+        // 0x3xkk | SE Vx, u8
+
+        return Instruction { .SE_3 = .{ .x = nib2, .kk = calc_u8(nib3, nib4) }};
+    } else if (nib1 == 0x6) {
+        // 0x6xkk | LD Vx, u8
+
+        return Instruction { .LD_6 = .{ .x = nib2, .kk = calc_u8(nib3, nib4) }};
+    } else if(nib1 == 0x7) {
+        // 0x7xkk | LD Vx, kk
+
+        return Instruction { .ADD_7 = .{ .x = nib2, .kk = calc_u8(nib3, nib4) }};
+    } else if (nib1 == 0xA) {
+        // 0xAnnn | LD I, addr
+        const addr = calc_u12(nib2, nib3, nib4);
+        return Instruction { .LD_I = addr };
+    } else if (nib1 == 0xD) {
+        // 0xDxyn | DRW Vx, Vy, n
+        return Instruction {.DRW = .{ .x = nib2, .y = nib3, .n = nib4 }};
+    }
+
+
+    return null;
+}
+
+pub fn execute(cpu: *Cpu, instr: Instruction) void {
+    switch (instr) {
+        .CLS => std.debug.print("CLS\n", .{}),
+        .RET => {
+            std.debug.print("RET\n", .{});
+
+            cpu.pc = cpu.stack[cpu.sp];
+            cpu.sp -= 1;
+        },
+        .JP => |addr| {
+            std.debug.print("JP 0x{X:}\n", .{ addr });
+
+            cpu.pc = addr;
+        },
+        .CALL => |addr| {
+            std.debug.print("CALL 0x{X:}\n", .{ addr });
+
+            cpu.sp += 1;
+            cpu.stack[cpu.sp] = cpu.pc;
+            cpu.pc = addr;
+        },
+        .SE_3 => |args| {
+            const x = args.x;
+            const kk = args.kk;
+            std.debug.print("SE V{}, 0x{X:}\n", .{ x, kk });
+
+            if (cpu.v[x] != kk) {
+                cpu.pc += 2;
+            }
+        },
+        .LD_6 => |args| {
+            const x = args.x;
+            const kk = args.kk;
+            std.debug.print("LD V{} 0x{X:}\n", .{ x, kk });
+
+            cpu.v[x] = kk;
+        },
+        .LD_I => |addr| {
+            std.debug.print("LD I, 0x{X:}\n", .{ addr });
+            cpu.i = addr;
+        },
+        .DRW => |args| {
+            const x = args.x;
+            const y = args.y;
+            const n = args.n;
+            std.debug.print("DRW V{}, V{}, 0x{X:}\n", .{ x, y, n });
+
+            const draw_pos: Point = .{ .x = cpu.v[x], .y = cpu.v[y] };
+            const sprite_data = cpu.memory[cpu.i..(cpu.i + n)];
+
+            // Draw Sprite
+            const collision = draw_sprite(&cpu.disp, &draw_pos, &sprite_data);
+
+            cpu.v[0xF] = if (collision) 1 else 0;
+            // Request Redraw
+        },
+        .ADD_7 => |args| {
+            const x = args.x;
+            const kk = args.kk;
+            std.debug.print("ADD V{}, 0x{X:}\n", .{ x, kk });
+
+            cpu.v[x] = cpu.v[x] + kk;
+        }
+    }
+}
+
+fn load_rom(cpu: *Cpu, buf: []u8) void {
+    var mem_index: usize = 0x200;
+
+    for (buf) |byte| {
+        cpu.memory[mem_index] = byte;
+        mem_index += 1;
+    }
+}
+
+pub fn load_rom_path(cpu: *Cpu, path: []const u8) !void {
+    var alloc = std.heap.page_allocator;
+
+    const file = try std.fs.cwd().openFile(path, .{ .read = true });
+    defer file.close();
+
+    const file_size = try file.getEndPos();
+    const rom_buf = try file.readToEndAlloc(alloc, file_size);
+
+    load_rom(cpu, rom_buf);
+}
+
+pub fn cycle(cpu: *Cpu) void {
+    const opcode = fetch(cpu);
+    const maybe_instr = decode(cpu, opcode);
+
+    if (maybe_instr) |instr| {
+        execute(cpu, instr);
+    } else {
+        panic("Unknown Opcode: 0x{X:}", . { opcode });
+    }
+}
+
+fn calc_u12(nib2: u4, nib3: u4, nib4: u4) u12 {
+    return @as(u12, nib2) << 8 | @as(u12, nib3) << 4 | @as(u12, nib4);
+}
+
+fn calc_u8(nib_a: u4, nib_b: u4) u8 {
+    return @as(u8, nib_a) << 4 | @as(u8, nib_b);
+}
+
+test "calc_u12 works" {
+    const left: u12 = 0xABC;
+    const right: u12 = calc_u12(0xA, 0xB, 0xC);
+
+    expect(left == right);
+}
+
+test "calc_u8 works" {
+    const left: u8 = 0xAB;
+    const right: u12 = calc_u8(0xA, 0xB);
+
+    expect(left == right);
+}

src/display.zig

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+const DISPLAY_WIDTH: usize = 64;
+const DISPLAY_HEIGHT: usize = 32;
+const std = @import("std");
+
+pub const Point = struct {
+    x: u16,
+    y: u16,
+};
+
+
+pub const Display =  struct {
+    buf: [DISPLAY_HEIGHT * DISPLAY_WIDTH]u8,
+
+
+    pub fn new() Display {
+        return .{
+            .buf = [_]u8{0x00} ** (DISPLAY_HEIGHT * DISPLAY_WIDTH)
+        };
+    }
+};
+
+pub fn clear(disp: *Display) void {
+    disp.buf = u8[DISPLAY_WIDTH * DISPLAY_HEIGHT]{0x00};
+}
+
+pub fn draw_sprite(disp: *Display, pos: *const Point, data: *const []u8) bool {
+    var set_vf: bool = false;
+
+    for (data.*) |byte, y_offset| {
+        var offset_count: u8 = 0;
+
+        while (offset_count < 8) : (offset_count += 1) {
+            const x_bit_offset = @intCast(u3, offset_count);
+            const x = @intCast(u8, pos.x + (7 - x_bit_offset));
+            const y = @intCast(u8, pos.y + y_offset);
+
+
+            const temp = (byte >> x_bit_offset) & 0x01;
+            const bit = @intCast(u1, temp);
+
+            const i = DISPLAY_WIDTH * y + x;
+
+            if (i >= disp.buf.len) break;
+
+            if (bit == 0x1 and disp.buf[i] == 0x01) {
+                set_vf = true;
+            }
+
+            disp.buf[i] ^= bit;
+        }
+    }
+
+
+    return set_vf;
+}

src/instructions.zig

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+
+pub const Instruction = union(enum) {
+    CLS: void,  // 0x00E0
+    RET: void,  // 0x00EE
+    JP: u12,    // 0x1nnn 
+    CALL: u12,  // 0x2nnn
+    SE_3: struct { x: u4, kk: u8 }, // 0x3xkk
+    LD_6: struct {x: u4, kk: u8}, // 0x6xkk
+    LD_I: u12,   // 0xAnnn
+    DRW: struct { x: u4, y: u4, n: u4 }, // 0xDxyn
+    ADD_7: struct { x: u4, kk: u8 } // 0x7xkk
+};

src/main.zig

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+const std = @import("std");
+const cpu = @import("cpu.zig");
+const Display = @import("display.zig").Display;
+const c = @cImport(@cInclude("SDL.h"));
+
+const WIDTH = 64;
+const HEIGHT = 32;
+
+
+pub fn main() anyerror!void {
+    _ = c.SDL_Init(c.SDL_INIT_VIDEO);
+    defer c.SDL_Quit();
+
+    const window = c.SDL_CreateWindow("CHIP-8", c.SDL_WINDOWPOS_CENTERED, c.SDL_WINDOWPOS_CENTERED, WIDTH, HEIGHT, c.SDL_WINDOW_OPENGL);
+    defer c.SDL_DestroyWindow(window);
+
+    const renderer = c.SDL_CreateRenderer(window, -1, c.SDL_RENDERER_ACCELERATED);
+    defer c.SDL_DestroyRenderer(renderer);
+
+    const texture = c.SDL_CreateTexture(renderer, c.SDL_PIXELFORMAT_RGBA8888, c.SDL_TEXTUREACCESS_STATIC, WIDTH, HEIGHT);
+    defer c.SDL_DestroyTexture(texture);
+
+
+    var zig8 = cpu.Cpu {
+        .i = 0x00,
+        .pc = 0x200,
+        .sp = 0x00,
+        .v = [_]u8{0x00} ** 16,
+        .stack = [_]u16{0x00} ** 16,
+        .memory = [_]u8{0x0000} ** 0x1000,
+        .disp = Display.new(),
+    };
+
+    try cpu.load_rom_path(&zig8, "./bin/IBM Logo.ch8");
+
+    const size = WIDTH * HEIGHT * @sizeOf(u32);
+    var pixels: [size]u8 = [_]u8 {0xFF} ** size;
+
+
+    emuloop: while(true) {
+        var event: c.SDL_Event = undefined;
+
+        while(c.SDL_PollEvent(&event) != 0) {
+            switch(event.type) {
+                c.SDL_QUIT => break :emuloop,
+                else => {}
+            }
+        }
+
+        var c_ptr = @ptrCast(*const c_void, &pixels);
+
+        _ = c.SDL_UpdateTexture(texture, null, c_ptr, WIDTH * @sizeOf(u32));
+    }
+}