0327-Chip8-随机数生成

环境

• Time 2023-07-27
• Zig 0.11.0-dev.4191+1bf16b172
• SLD2 2.28.1

前言

说明

参考资料：

1. https://en.wikipedia.org/wiki/CHIP-8
2. https://austinmorlan.com/posts/chip8_emulator/
3. https://rsj217.github.io/chip8-py/
4. https://github.com/Timendus/chip8-test-suite

其中最后一个提供了测试的套件，实现的过程中，可以检测哪些指令有问题，帮助很大。

目标

实现随机数生成，其中 CXNN 指令使用到了随机数。

prng

其它无关代码已省略，新增随机数生成。

pub const CPU = struct {
    instruct: Instruct = undefined,
    register: [16]u8 = std.mem.zeroes([16]u8),
    index: u16 = 0,
    pc: u16,
    prng: std.rand.DefaultPrng,

    pub fn new(entry: u16) CPU {
        const seed = @as(u64, @intCast(std.time.timestamp()));
        var prng = std.rand.DefaultPrng.init(seed);
        return CPU{
            .pc = entry,
            .prng = prng,
        };
    }
}

CXNN

  0xC => reg[ins.x] = self.prng.random().int(u8) & ins.nn,

chip8.zig

修改了 CPU 的初始化方式。

const cpu = @import("cpu.zig");
const memory = @import("memory.zig");
const screen = @import("screen.zig");
const keypad = @import("keypad.zig");

const ENTRY = 0x200;
const HZ = 500;
const FPS = 60;

pub const Emulator = struct {
    cpu: cpu.CPU,
    memory: memory.Memory,
    screen: screen.Screen,
    keypad: keypad.Keypad,

    pub fn new(rom: []const u8) Emulator {
        return Emulator{
            .cpu = cpu.CPU.new(ENTRY),
            .memory = memory.Memory.new(rom, ENTRY),
            .screen = screen.Screen{},
            .keypad = keypad.Keypad{},
        };
    }

    pub fn run(self: *Emulator) void {
        self.screen.init();
        defer self.screen.deinit();
        self.memory.screen = &self.screen;
        self.memory.keypad = &self.keypad;

        var index: usize = 0;
        while (self.keypad.poll()) : (index += 1) {
            for (0..(HZ / FPS)) |_|
                self.cpu.cycle(&self.memory);

            self.screen.update(FPS);
        }
    }
};

启动

zig build run

效果

总结

实现了 CXNN 指令，包含其中的随机数生成。

附录