From e737cda649acbfa43fc1b74612a83f2fac9aa449 Mon Sep 17 00:00:00 2001
From: Eric Laurent <elaurent@google.com>
Date: Tue, 22 May 2012 18:55:44 -0700
Subject: audioflinger: refine latency latency calculation.

There is an audio pipe between the normal mixer output and the fast
mixer to cope for scheduling delays and buffer size difference.
This pipe depth was not taken into account in latency calculation.

Adding the pipe contribution to the latency significantly improves A/V sync.

Bug 6520569.

Change-Id: I5584908e8aa8a02170eb38b22b4370eea800a235
---
 services/audioflinger/AudioFlinger.cpp | 17 ++++++++++++++++-
 services/audioflinger/AudioFlinger.h   |  3 +++
 services/audioflinger/MonoPipe.h       |  4 ++++
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/services/audioflinger/AudioFlinger.cpp b/services/audioflinger/AudioFlinger.cpp
index 3c60e5a..68be7a7 100644
--- a/services/audioflinger/AudioFlinger.cpp
+++ b/services/audioflinger/AudioFlinger.cpp
@@ -1804,11 +1804,25 @@ Exit:
     return track;
 }
 
+uint32_t AudioFlinger::MixerThread::correctLatency(uint32_t latency) const
+{
+    if (mFastMixer != NULL) {
+        MonoPipe *pipe = (MonoPipe *)mPipeSink.get();
+        latency += (pipe->getAvgFrames() * 1000) / mSampleRate;
+    }
+    return latency;
+}
+
+uint32_t AudioFlinger::PlaybackThread::correctLatency(uint32_t latency) const
+{
+    return latency;
+}
+
 uint32_t AudioFlinger::PlaybackThread::latency() const
 {
     Mutex::Autolock _l(mLock);
     if (initCheck() == NO_ERROR) {
-        return mOutput->stream->get_latency(mOutput->stream);
+        return correctLatency(mOutput->stream->get_latency(mOutput->stream));
     } else {
         return 0;
     }
@@ -2020,6 +2034,7 @@ void AudioFlinger::PlaybackThread::readOutputParameters()
     }
 }
 
+
 status_t AudioFlinger::PlaybackThread::getRenderPosition(uint32_t *halFrames, uint32_t *dspFrames)
 {
     if (halFrames == NULL || dspFrames == NULL) {
diff --git a/services/audioflinger/AudioFlinger.h b/services/audioflinger/AudioFlinger.h
index 1ae5414..51cbae7 100644
--- a/services/audioflinger/AudioFlinger.h
+++ b/services/audioflinger/AudioFlinger.h
@@ -1048,6 +1048,8 @@ public:
         // Cache various calculated values, at threadLoop() entry and after a parameter change
         virtual     void        cacheParameters_l();
 
+        virtual     uint32_t    correctLatency(uint32_t latency) const;
+
     private:
 
         friend class AudioFlinger;      // for numerous
@@ -1154,6 +1156,7 @@ public:
         virtual     void        threadLoop_mix();
         virtual     void        threadLoop_sleepTime();
         virtual     void        threadLoop_removeTracks(const Vector< sp<Track> >& tracksToRemove);
+        virtual     uint32_t    correctLatency(uint32_t latency) const;
 
                     AudioMixer* mAudioMixer;    // normal mixer
     private:
diff --git a/services/audioflinger/MonoPipe.h b/services/audioflinger/MonoPipe.h
index 1f56e54..545d6ac 100644
--- a/services/audioflinger/MonoPipe.h
+++ b/services/audioflinger/MonoPipe.h
@@ -56,6 +56,10 @@ public:
     virtual ssize_t write(const void *buffer, size_t count);
     //virtual ssize_t writeVia(writeVia_t via, size_t total, void *user, size_t block);
 
+            // average number of frames present in the pipe under normal conditions.
+            // See throttling mechanism in MonoPipe::write()
+            size_t  getAvgFrames() const { return (mMaxFrames * 11) / 16; }
+
 private:
     const size_t    mMaxFrames;     // always a power of 2
     void * const    mBuffer;
-- 
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