diff --git a/services/audioflinger/AudioFlinger.cpp b/services/audioflinger/AudioFlinger.cpp
index 83af5f3..fb5a7e1 100644
--- a/services/audioflinger/AudioFlinger.cpp
+++ b/services/audioflinger/AudioFlinger.cpp
@@ -1924,7 +1924,7 @@
 }
 
 // this method must always be called either with ThreadBase mLock held or inside the thread loop
-audio_stream_t* AudioFlinger::PlaybackThread::stream()
+audio_stream_t* AudioFlinger::PlaybackThread::stream() const
 {
     if (mOutput == NULL) {
         return NULL;
@@ -1932,7 +1932,7 @@
     return &mOutput->stream->common;
 }
 
-uint32_t AudioFlinger::PlaybackThread::activeSleepTimeUs()
+uint32_t AudioFlinger::PlaybackThread::activeSleepTimeUs() const
 {
     // A2DP output latency is not due only to buffering capacity. It also reflects encoding,
     // decoding and transfer time. So sleeping for half of the latency would likely cause
@@ -2817,12 +2817,12 @@
     return NO_ERROR;
 }
 
-uint32_t AudioFlinger::MixerThread::idleSleepTimeUs()
+uint32_t AudioFlinger::MixerThread::idleSleepTimeUs() const
 {
     return (uint32_t)(((mFrameCount * 1000) / mSampleRate) * 1000) / 2;
 }
 
-uint32_t AudioFlinger::MixerThread::suspendSleepTimeUs()
+uint32_t AudioFlinger::MixerThread::suspendSleepTimeUs() const
 {
     return (uint32_t)(((mFrameCount * 1000) / mSampleRate) * 1000);
 }
@@ -3166,7 +3166,7 @@
     return reconfig;
 }
 
-uint32_t AudioFlinger::DirectOutputThread::activeSleepTimeUs()
+uint32_t AudioFlinger::DirectOutputThread::activeSleepTimeUs() const
 {
     uint32_t time;
     if (audio_is_linear_pcm(mFormat)) {
@@ -3177,7 +3177,7 @@
     return time;
 }
 
-uint32_t AudioFlinger::DirectOutputThread::idleSleepTimeUs()
+uint32_t AudioFlinger::DirectOutputThread::idleSleepTimeUs() const
 {
     uint32_t time;
     if (audio_is_linear_pcm(mFormat)) {
@@ -3188,7 +3188,7 @@
     return time;
 }
 
-uint32_t AudioFlinger::DirectOutputThread::suspendSleepTimeUs()
+uint32_t AudioFlinger::DirectOutputThread::suspendSleepTimeUs() const
 {
     uint32_t time;
     if (audio_is_linear_pcm(mFormat)) {
@@ -3351,7 +3351,7 @@
     return true;
 }
 
-uint32_t AudioFlinger::DuplicatingThread::activeSleepTimeUs()
+uint32_t AudioFlinger::DuplicatingThread::activeSleepTimeUs() const
 {
     return (mWaitTimeMs * 1000) / 2;
 }
@@ -5623,7 +5623,7 @@
 }
 
 // this method must always be called either with ThreadBase mLock held or inside the thread loop
-audio_stream_t* AudioFlinger::RecordThread::stream()
+audio_stream_t* AudioFlinger::RecordThread::stream() const
 {
     if (mInput == NULL) {
         return NULL;
diff --git a/services/audioflinger/AudioFlinger.h b/services/audioflinger/AudioFlinger.h
index 2376aff..3051514 100644
--- a/services/audioflinger/AudioFlinger.h
+++ b/services/audioflinger/AudioFlinger.h
@@ -472,7 +472,7 @@
                     audio_io_handle_t id() const { return mId;}
                     bool        standby() const { return mStandby; }
                     uint32_t    device() const { return mDevice; }
-        virtual     audio_stream_t* stream() = 0;
+        virtual     audio_stream_t* stream() const = 0;
 
                     sp<EffectHandle> createEffect_l(
                                         const sp<AudioFlinger::Client>& client,
@@ -918,7 +918,7 @@
 
                     AudioStreamOut* getOutput() const;
                     AudioStreamOut* clearOutput();
-                    virtual audio_stream_t* stream();
+                    virtual audio_stream_t* stream() const;
 
                     void        suspend() { mSuspended++; }
                     void        restore() { if (mSuspended > 0) mSuspended--; }
@@ -960,9 +960,13 @@
         // Allocate a track name.  Returns name >= 0 if successful, -1 on failure.
         virtual int             getTrackName_l() = 0;
         virtual void            deleteTrackName_l(int name) = 0;
-        virtual uint32_t        activeSleepTimeUs();
-        virtual uint32_t        idleSleepTimeUs() = 0;
-        virtual uint32_t        suspendSleepTimeUs() = 0;
+
+        // Time to sleep between cycles when:
+        virtual uint32_t        activeSleepTimeUs() const;      // mixer state MIXER_TRACKS_ENABLED
+        virtual uint32_t        idleSleepTimeUs() const = 0;    // mixer state MIXER_IDLE
+        virtual uint32_t        suspendSleepTimeUs() const = 0; // audio policy manager suspended us
+        // No sleep when mixer state == MIXER_TRACKS_READY; relies on audio HAL stream->write()
+        // No sleep in standby mode; waits on a condition
 
         // Code snippets that are temporarily lifted up out of threadLoop() until the merge
                     void        checkSilentMode_l();
@@ -1048,8 +1052,8 @@
         virtual     mixer_state prepareTracks_l(Vector< sp<Track> > *tracksToRemove);
         virtual     int         getTrackName_l();
         virtual     void        deleteTrackName_l(int name);
-        virtual     uint32_t    idleSleepTimeUs();
-        virtual     uint32_t    suspendSleepTimeUs();
+        virtual     uint32_t    idleSleepTimeUs() const;
+        virtual     uint32_t    suspendSleepTimeUs() const;
         virtual     void        cacheParameters_l();
 
         // threadLoop snippets
@@ -1073,9 +1077,9 @@
     protected:
         virtual     int         getTrackName_l();
         virtual     void        deleteTrackName_l(int name);
-        virtual     uint32_t    activeSleepTimeUs();
-        virtual     uint32_t    idleSleepTimeUs();
-        virtual     uint32_t    suspendSleepTimeUs();
+        virtual     uint32_t    activeSleepTimeUs() const;
+        virtual     uint32_t    idleSleepTimeUs() const;
+        virtual     uint32_t    suspendSleepTimeUs() const;
         virtual     void        cacheParameters_l();
 
         // threadLoop snippets
@@ -1110,9 +1114,9 @@
         // Thread virtuals
                     void        addOutputTrack(MixerThread* thread);
                     void        removeOutputTrack(MixerThread* thread);
-                    uint32_t    waitTimeMs() { return mWaitTimeMs; }
+                    uint32_t    waitTimeMs() const { return mWaitTimeMs; }
     protected:
-        virtual     uint32_t    activeSleepTimeUs();
+        virtual     uint32_t    activeSleepTimeUs() const;
 
     private:
                     bool        outputsReady(const SortedVector< sp<OutputTrack> > &outputTracks);
@@ -1260,7 +1264,7 @@
                 status_t    dump(int fd, const Vector<String16>& args);
                 AudioStreamIn* getInput() const;
                 AudioStreamIn* clearInput();
-                virtual audio_stream_t* stream();
+                virtual audio_stream_t* stream() const;
 
         // AudioBufferProvider interface
         virtual status_t    getNextBuffer(AudioBufferProvider::Buffer* buffer, int64_t pts);