audio: Wait for samples on the emulated DSP side to avoid desyncs

Waiting on the host side is inaccurate and leads to desyncs in the event of the sink missing a deadline that require stalls to fix. By waiting for the sink to have space before even starting rendering such desyncs can be avoided.

src/audio_core/renderer/adsp/audio_renderer.cpp

@@ -189,6 +189,8 @@ void AudioRenderer::ThreadFunc() {
                     max_time = std::min(command_buffer.time_limit, max_time);
                     command_list_processor.SetProcessTimeMax(max_time);
 
+                    streams[index]->WaitFreeSpace();
+
                     // Process the command list
                     {
                         MICROPROFILE_SCOPE(Audio_Renderer);

src/audio_core/renderer/adsp/audio_renderer.h

@@ -12,6 +12,7 @@
 #include "common/common_types.h"
 #include "common/reader_writer_queue.h"
 #include "common/thread.h"
+#include "common/polyfill_thread.h"
 
 namespace Core {
 namespace Timing {

src/audio_core/renderer/system_manager.cpp

@@ -17,11 +17,7 @@ MICROPROFILE_DEFINE(Audio_RenderSystemManager, "Audio", "Render System Manager",
 namespace AudioCore::AudioRenderer {
 
 SystemManager::SystemManager(Core::System& core_)
-    : core{core_}, adsp{core.AudioCore().GetADSP()}, mailbox{adsp.GetRenderMailbox()},
-      thread_event{Core::Timing::CreateEvent(
-          "AudioRendererSystemManager", [this](std::uintptr_t, s64 time, std::chrono::nanoseconds) {
-              return ThreadFunc2(time);
-          })} {}
+    : core{core_}, adsp{core.AudioCore().GetADSP()}, mailbox{adsp.GetRenderMailbox()} {}
 
 SystemManager::~SystemManager() {
     Stop();
@@ -32,8 +28,6 @@ bool SystemManager::InitializeUnsafe() {
         if (adsp.Start()) {
             active = true;
             thread = std::jthread([this](std::stop_token stop_token) { ThreadFunc(); });
-            core.CoreTiming().ScheduleLoopingEvent(std::chrono::nanoseconds(0), RENDER_TIME,
-                                                   thread_event);
         }
     }
 
@@ -44,7 +38,6 @@ void SystemManager::Stop() {
     if (!active) {
         return;
     }
-    core.CoreTiming().UnscheduleEvent(thread_event, {});
     active = false;
     update.store(true);
     update.notify_all();
@@ -110,16 +103,7 @@ void SystemManager::ThreadFunc() {
 
         adsp.Signal();
         adsp.Wait();
-
-        update.wait(false);
-        update.store(false);
     }
 }
 
-std::optional<std::chrono::nanoseconds> SystemManager::ThreadFunc2(s64 time) {
-    update.store(true);
-    update.notify_all();
-    return std::nullopt;
-}
-
 } // namespace AudioCore::AudioRenderer

src/audio_core/renderer/system_manager.h

@@ -68,11 +68,6 @@ private:
      */
     void ThreadFunc();
 
-    /**
-     * Signalling core timing thread to run ThreadFunc.
-     */
-    std::optional<std::chrono::nanoseconds> ThreadFunc2(s64 time);
-
     enum class StreamState {
         Filling,
         Steady,
@@ -95,8 +90,6 @@ private:
     ADSP::ADSP& adsp;
     /// AudioRenderer mailbox for communication
     ADSP::AudioRenderer_Mailbox* mailbox{};
-    /// Core timing event to signal main thread
-    std::shared_ptr<Core::Timing::EventType> thread_event;
     /// Atomic for main thread to wait on
     std::atomic<bool> update{};
 };

src/audio_core/sink/sink_stream.cpp

@@ -205,6 +205,10 @@ void SinkStream::ProcessAudioOutAndRender(std::span<s16> output_buffer, std::siz
     // If we're paused or going to shut down, we don't want to consume buffers as coretiming is
     // paused and we'll desync, so just play silence.
     if (system.IsPaused() || system.IsShuttingDown()) {
+        if (system.IsShuttingDown()) {
+            release_cv.notify_one();
+        }
+
         static constexpr std::array<s16, 6> silence{};
         for (size_t i = frames_written; i < num_frames; i++) {
             std::memcpy(&output_buffer[i * frame_size], &silence[0], frame_size_bytes);
@@ -240,6 +244,12 @@ void SinkStream::ProcessAudioOutAndRender(std::span<s16> output_buffer, std::siz
             }
             // Successfully dequeued a new buffer.
             queued_buffers--;
+
+            {
+                std::unique_lock lk{release_mutex};
+            }
+
+            release_cv.notify_one();
         }
 
         // Get the minimum frames available between the currently playing buffer, and the
@@ -303,4 +313,9 @@ u64 SinkStream::GetExpectedPlayedSampleCount() {
     return std::min<u64>(exp_played_sample_count, max_played_sample_count);
 }
 
+void SinkStream::WaitFreeSpace() {
+    std::unique_lock lk{release_mutex};
+    release_cv.wait(lk, [this]() { return queued_buffers < max_queue_size || system.IsShuttingDown(); });
+}
+
 } // namespace AudioCore::Sink

src/audio_core/sink/sink_stream.h

@@ -16,6 +16,7 @@
 #include "common/reader_writer_queue.h"
 #include "common/ring_buffer.h"
 #include "common/thread.h"
+#include "common/polyfill_thread.h"
 
 namespace Core {
 class System;
@@ -219,6 +220,11 @@ public:
      */
     u64 GetExpectedPlayedSampleCount();
 
+    /**
+     * Waits for free space in the sample ring buffer
+     */
+    void WaitFreeSpace();
+
 protected:
     /// Core system
     Core::System& system;
@@ -258,6 +264,9 @@ private:
     f32 system_volume{1.0f};
     /// Set via IAudioDevice service calls
     f32 device_volume{1.0f};
+    /// Signalled when ring buffer entries are consumed
+    std::condition_variable release_cv;
+    std::mutex release_mutex;
     std::mutex stall_guard;
     std::unique_lock<std::mutex> stalled_lock;
 };