Initial Commit

This commit is contained in:
Rekai Nyangadzayi Musuka 2021-06-17 00:45:23 -05:00
commit 4ef56bbcaf
6 changed files with 361 additions and 0 deletions

8
.gitignore vendored Normal file
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# Zig Build Directories
/zig-cache
/zig-out
# ROM directory
/bin

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build.zig Normal file
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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);
}

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src/cpu.zig Normal file
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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);
}

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src/display.zig Normal file
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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;
}

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src/instructions.zig Normal file
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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
};

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src/main.zig Normal file
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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));
}
}