Yi8

A very simple emulator for the CHIP-8 architecture.

Build

Just run tsc and serve the index.html with any webserver. python3 -m http.server for example.

Usage

To start the emulator click the select a file button and select your rom. Keybinds are

1 2 3 4
q w e r
a s d f
y x c v

Notes

Timings in Javascript is pretty hard. Currently I get a somewhat accurate implementation by using requestAnimationFrame and generating a delta between the calls.

let interfaceRefreshRate = 10; // HZ
let displayRefreshRate = 30; // HZ

let ifTick = 0;
let dpTick = 0;

const ifTickTarget = (1 / interfaceRefreshRate) * 1000; // ms
const dpTickTarget = (1 / displayRefreshRate) * 1000; // ms

const tick = (t: number) => {
	const delta = t - t1;
	const ticks = (state.clockSpeed / 1000) * delta;
	t1 = t;

	for (let i = 0; i < ticks; i++) {
		CPU.fetch(state);
		CPU.decode(state);
		CPU.exec(state);
	}

	dpTick += delta;
	if (dpTick > dpTickTarget) {
		// Render screen 
		dpTick = 0; 
	}

	ifTick += delta;
	if (ifTick > ifTickTarget) {
		// Render interface
		ifTick = 0; 
	}

	requestAnimationFrame(tick);
}