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feat: reimplement audio sync

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APU will now drop samples if the Audio Queue is already full, therefore
creating a "sped-up" effect when the emulator runs faster than 100%
This commit is contained in:
Rekai Nyangadzayi Musuka
2022-09-08 20:38:42 -03:00
parent fa862f095a
commit 65cfc97f28
3 changed files with 58 additions and 33 deletions
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41
src/core/emu.zig
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@@ -70,12 +70,21 @@ pub fn runFrame(sched: *Scheduler, cpu: *Arm7tdmi) void {
}
}
fn syncToAudio(cpu: *const Arm7tdmi) void {
const stream = cpu.bus.apu.stream;
const min_sample_count = 0x800;
fn syncToAudio(stream: *SDL.SDL_AudioStream, is_buffer_full: *bool) void {
const sample_size = 2 * @sizeOf(u16);
const max_buf_size: c_int = 0x400;
// Busy Loop while we wait for the Audio system to catch up
while (SDL.SDL_AudioStreamAvailable(stream) > (@sizeOf(u16) * 2) * min_sample_count) {}
// Determine whether the APU is busy right at this moment
var still_full: bool = SDL.SDL_AudioStreamAvailable(stream) > sample_size * if (is_buffer_full.*) max_buf_size >> 1 else max_buf_size;
defer is_buffer_full.* = still_full; // Update APU Busy status right before exiting scope
// If Busy is false, there's no need to sync here
if (!still_full) return;
while (true) {
still_full = SDL.SDL_AudioStreamAvailable(stream) > sample_size * max_buf_size >> 1;
if (!sync_audio or !still_full) break;
}
}
pub fn runUnsynchronized(quit: *Atomic(bool), sched: *Scheduler, cpu: *Arm7tdmi, fps: ?*FpsTracker) void {
@@ -86,21 +95,21 @@ pub fn runUnsynchronized(quit: *Atomic(bool), sched: *Scheduler, cpu: *Arm7tdmi,
while (!quit.load(.SeqCst)) {
runFrame(sched, cpu);
if (sync_audio) syncToAudio(cpu);
syncToAudio(cpu.bus.apu.stream, &cpu.bus.apu.is_buffer_full);
tracker.tick();
}
} else {
while (!quit.load(.SeqCst)) {
runFrame(sched, cpu);
if (sync_audio) syncToAudio(cpu);
syncToAudio(cpu.bus.apu.stream, &cpu.bus.apu.is_buffer_full);
}
}
}
pub fn runSynchronized(quit: *Atomic(bool), sched: *Scheduler, cpu: *Arm7tdmi, fps: ?*FpsTracker) void {
log.info("Emulation thread w/ video sync", .{});
var timer = Timer.start() catch unreachable;
var timer = Timer.start() catch std.debug.panic("Failed to initialize std.timer.Timer", .{});
var wake_time: u64 = frame_period;
if (fps) |tracker| {
@@ -108,13 +117,14 @@ pub fn runSynchronized(quit: *Atomic(bool), sched: *Scheduler, cpu: *Arm7tdmi, f
while (!quit.load(.SeqCst)) {
runFrame(sched, cpu);
const new_wake_time = syncToVideo(&timer, wake_time);
const new_wake_time = blockOnVideo(&timer, wake_time);
// Spin to make up the difference of OS scheduler innacuracies
// If we happen to also be syncing to audio, we choose to spin on
// the amount of time needed for audio to catch up rather than
// our expected wake-up time
if (sync_audio) syncToAudio(cpu) else spinLoop(&timer, wake_time);
syncToAudio(cpu.bus.apu.stream, &cpu.bus.apu.is_buffer_full);
if (!sync_audio) spinLoop(&timer, wake_time);
wake_time = new_wake_time;
tracker.tick();
@@ -122,16 +132,17 @@ pub fn runSynchronized(quit: *Atomic(bool), sched: *Scheduler, cpu: *Arm7tdmi, f
} else {
while (!quit.load(.SeqCst)) {
runFrame(sched, cpu);
const new_wake_time = syncToVideo(&timer, wake_time);
// see above comment
if (sync_audio) syncToAudio(cpu) else spinLoop(&timer, wake_time);
const new_wake_time = blockOnVideo(&timer, wake_time);
// see above comment
syncToAudio(cpu.bus.apu.stream, &cpu.bus.apu.is_buffer_full);
if (!sync_audio) spinLoop(&timer, wake_time);
wake_time = new_wake_time;
}
}
}
inline fn syncToVideo(timer: *Timer, wake_time: u64) u64 {
inline fn blockOnVideo(timer: *Timer, wake_time: u64) u64 {
// Use the OS scheduler to put the emulation thread to sleep
const maybe_recalc_wake_time = sleep(timer, wake_time);
@@ -149,6 +160,8 @@ pub fn runBusyLoop(quit: *Atomic(bool), sched: *Scheduler, cpu: *Arm7tdmi) void
runFrame(sched, cpu);
spinLoop(&timer, wake_time);
syncToAudio(cpu.bus.apu.stream, &cpu.bus.apu.is_buffer_full);
// Update to the new wake time
wake_time += frame_period;
}