Concurrency

[fengb]

All of the sub-components are independent hardware. To model this correctly, we should push each one onto a separate thread.

MMU is the biggest problem since it's effectively global memory, but the Gameboy has some well-defined semantics around it. We might need to rethink IO.

[fengb]

Potential solution:

• Every unit owns its own "private" memory space with free read/write
• When reading from global, it receives memory that's effectively at the beginning of runloop.
• When communicating outside its space, we need to defer the actual writes to end of runloop.

With these, the main loop can become:

while (track >= 0) : (track -= 4) {
    const mmu = fd.mmu;

    // mmu is now const
    const cpu = async fd.cpu.step(mmu, 4);
    const video = async fd.video.step(mmu, 4);
    const timer = async fd.timer.step(mmu, 4);
    const audio = async fd.audio.step(mmu, 4);

    fd.mmu.apply(await cpu);
    fd.mmu.apply(await video);
    fd.mmu.apply(await timer);
    fd.mmu.apply(await audio);
}

Yes this reinvents Erlang actors.