pvbemu/app/Emulator.js

"use strict";

// Worker that manages a WebAssembly instance of the C core library
(globalThis.Emulator = class Emulator {

    // Static initializer
    static initializer() {
        new Emulator();
    }

    // Object constructor
    constructor() {

        // Configure instance fields
        this.buffers = {};

        // Configure message port
        onmessage = e=>this.onmessage(e.data);
    }



    ///////////////////////////// Message Methods /////////////////////////////

    // Message received
    onmessage(msg) {
        switch (msg.command) {
            case "Init"      : this.init      (msg); break;
            case "ReadBuffer": this.readBuffer(msg); break;
            case "SetROM"    : this.setROM    (msg); break;
        }
    }

    // Initialize the WebAssembly core module
    async init(msg) {

        // Load and instantiate the WebAssembly module
        this.wasm = await WebAssembly.instantiate(msg.wasm,
            { env: { emscripten_notify_memory_growth: ()=>this.onmemory() }});
        this.wasm.instance.exports.Init();

        // Configure instance fields
        this.core = this.wasm.instance.exports;

        postMessage({ command: "Init" });
    }

    // Read multiple data units from the bus
    readBuffer(msg) {
        let buffer = this.malloc(Uint8Array, msg.size);
        this.core.ReadBuffer(msg.sim, buffer.pointer, msg.address, msg.size);
        msg.buffer = this.core.memory.buffer.slice(
            buffer.pointer, buffer.pointer + msg.size);
        this.free(buffer);
        postMessage(msg, msg.buffer);
    }

    // Supply a ROM buffer
    setROM(msg) {
        let rom    = new Uint8Array(msg.rom);
        let buffer = this.malloc(Uint8Array, rom.length);
        for (let x = 0; x < rom.length; x++)
            buffer.data[x] = rom[x];
        msg.success = !!this.core.SetROM(msg.sim, buffer.pointer, rom.length);
        delete msg.rom;
        postMessage(msg);
    }



    ///////////////////////////// Private Methods /////////////////////////////

    // Delete a previously-allocated memory buffer
    free(buffer) {
        this.core.Free(buffer.pointer);
        delete this.buffers[buffer.pointer];
    }

    // Allocate a typed array in WebAssembly core memory
    malloc(type, size) {
        let pointer = this.core.Malloc(size);
        let data    = new type(this.core.memory.buffer, pointer, size);
        return this.buffers[pointer] = { data: data, pointer: pointer };
    }

    // WebAssembly memory has grown
    onmemory() {
        for (let buffer of Object.values(this.buffers)) {
            buffer.data = new buffer.data.constructor(
                this.core.memory.buffer, buffer.pointer);
        }
    }

}).initializer();