System: Reset throttler when audio buffers underflow

Should hopefully reduce the chances of the audio source ending up out of
phase from the emulation when vsync is disabled.

src/core/system.cpp

@@ -1216,8 +1216,22 @@ void UpdateThrottlePeriod()
     static_cast<s32>(1000000000.0 / static_cast<double>(s_throttle_frequency) / static_cast<double>(s_target_speed));
 }
 
+void ResetThrottler()
+{
+  s_last_throttle_time = 0;
+  s_throttle_timer.Reset();
+}
+
 void Throttle()
 {
+  // Reset the throttler on audio buffer overflow, so we don't end up out of phase.
+  if (g_host_interface->GetAudioStream()->DidUnderflow())
+  {
+    Log_DevPrintf("Audio buffer underflowed, resetting throttler");
+    ResetThrottler();
+    return;
+  }
+
   // Allow variance of up to 40ms either way.
   constexpr s64 MAX_VARIANCE_TIME = INT64_C(40000000);
 
@@ -1239,8 +1253,7 @@ void Throttle()
       s_speed_lost_time_timestamp.Reset();
     }
 #endif
-    s_last_throttle_time = 0;
-    s_throttle_timer.Reset();
+    ResetThrottler();
   }
   else if (sleep_time >= MINIMUM_SLEEP_TIME)
   {
@@ -1294,8 +1307,7 @@ void ResetPerformanceCounters()
   s_average_frame_time_accumulator = 0.0f;
   s_worst_frame_time_accumulator = 0.0f;
   s_fps_timer.Reset();
-  s_throttle_timer.Reset();
-  s_last_throttle_time = 0;
+  ResetThrottler();
 }
 
 bool LoadEXE(const char* filename)

src/core/system.h

@@ -154,6 +154,7 @@ void SetThrottleFrequency(float frequency);
 
 /// Updates the throttle period, call when target emulation speed changes.
 void UpdateThrottlePeriod();
+void ResetThrottler();
 
 /// Throttles the system, i.e. sleeps until it's time to execute the next frame.
 void Throttle();