Create initial emulator and hello world demo

emu.js

@@ -0,0 +1,69 @@
+const TXBUF = 0;
+const RXBUF = 32;
+const TXDATA = 64;
+const TXHEAD = 65;
+const TXTAIL = 66;
+const RXDATA = 67;
+const RXHEAD = 68;
+const RXTAIL = 69;
+
+const TXBUF_SIZE = 32;
+const RXBUF_SIZE = 32;
+const PERIPHS_SIZE = 70;
+
+const POLL_INTERVAL_MS = 20;
+
+class Emulator {
+	constructor() {
+		this.mem = new WebAssembly.Memory({
+			initial: 1,
+			maximum: 1,
+			shared: true
+		});
+		this.mem_u8 = new Uint8Array(this.mem.buffer);
+		for (let i = 0; i < PERIPHS_SIZE; ++i)
+			this.mem_u8[i] = 0;
+
+		this.decoder = new TextDecoder('utf-8');
+
+		this.output = document.getElementById('output');
+		this.input = document.getElementById('input');
+
+		this.timer = setInterval(() => this.poll(), POLL_INTERVAL_MS);
+
+		this.worker = new Worker('boot.js');
+		this.worker.postMessage(this.mem);
+	}
+
+	poll() {
+		const txdata = Atomics.load(this.mem_u8, TXDATA);
+		if (txdata !== 0)
+			this.handle_txdata();
+	}
+
+	handle_txdata() {
+		const head = Atomics.load(this.mem_u8, TXHEAD);
+		const tail = Atomics.load(this.mem_u8, TXTAIL);
+
+		const data = [];
+		let i = head;
+		do {
+			data.push(this.mem_u8[TXBUF + i]);
+			i = (i + 1) % TXBUF_SIZE;
+		} while (i !== tail);
+
+		Atomics.store(this.mem_u8, TXHEAD, tail);
+
+		// More data could have been added -- only clear TXDATA if
+		// tail is unchanged.
+		if (tail === Atomics.load(this.mem_u8, TXTAIL))
+			Atomics.store(this.mem_u8, TXDATA, 0);
+
+		const str = this.decoder.decode(new Uint8Array(data));
+		this.output.innerText += str;
+	}
+}
+
+window.addEventListener('DOMContentLoaded', () => {
+	window.emu = new Emulator();
+});