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HAL Layer代码位置：~hardwarealsa_sound*.*;
~hardwarelibhardware_legacyincludehardware_legacy*.*
~hardwaremx5xmodulesalsaalsa_imx5x.cpp
~hardwarealsa_soundAudioHardwareALSA.cpp
~hardwarealsa_soundALSAStreamOps.cpp
~hardwarealsa_soundAudioStreamOutALSA.cpp
~hardwarealsa_soundAudioStreamInALSA.cpp
~hardwarealsa_soundALSAControl.cpp
~hardwarealsa_soundALSAMixer.cpp
~hardwarelibhardware_legacyincludehardware_legacyAudioHardwareBase.h
~hardwarelibhardware_legacyincludehardware_legacyAudioHardwareInterface.h
~hardwarelibhardware_legacyincludehardware_legacyAudioPolicyInterface.h
~hardwarelibhardware_legacyincludehardware_legacyAudioPolicyManagerBase.h

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Alsa Lib Layer代码位置：~externalalsa-libsrcpcm*.*
~externalalsa-libsrcpcmpcm.c
~externalalsa-libsrcpcmPcm_empty.c
~externalalsa-libsrcpcmPcm_asym.c
~externalalsa-libsrcpcmPcm_plug.c
~externalalsa-libsrcpcmpcm_dmix.c
~externalalsa-libsrcpcmPcm_hw.c
~externalalsa-libsrcpcmPcmparams.c
~externalalsa-libsrcpcmPcmpcm_direct.c
~externalalsa-libsrcpcmPcmpcm_local.h
Alsa Driver Layer代码位置：~kernel_imxsoundcore*.*
~kernel_imxsoundcorePcm_native.c
~kernel_imxsoundcorePcm_lib.c
~kernel_imxsoundcoreSoc-core.c
~kernel_imxsoundSocSoc-dapm.c

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MediaPlaybackService.java----ServiceStub—play(mService:MediaPlaybackService)
MediaPlaybackService.java----MediaPlaybackService—play(mPlayer:MultiPlayer)
MediaPlaybackService.java---- MultiPlayer—start
MediaPlayer.java----MediaPlayer—start
MediaPlayer.java----MediaPlayer—_start
Android_media_MediaPlayer.cpp---- android_media_MediaPlayer_start(mp:MediaPlayer)
Android_media_MediaPlayer.cpp----mp->start
MediaPlayer.cpp----start(mPlayer: IMediaPlayer)
IMediaPlayer.cpp----start
IMediaPlayer.cpp----remote()->transact(START, data, &reply)
IMediaPlayer.cpp----BnMediaPlayer::onTransact
IMediaPlayer.cpp----START--reply->writeInt32(start());
MediaPlayerService.cpp----MediaPlayerService::Client::start ()(p:MediaPlayerBase)
MediaPlayerService.cpp----MediaPlayerService::AudioOutput::start ()
MediaPlayerService.cpp----mTrack->pause()(mTrack:AudioTrack--TrackHandle)
AudioFlinger.cpp----AudioFlinger::TrackHandle::start()(mTrack: Track)
AudioFlinger.cpp----AudioFlinger::PlaybackThread::Track::start()
AudioFlinger.cpp----AudioSystem::startOutput
AudioFlinger.cpp----AudioSystem::startOutput
AudioSystem.cpp---- aps-> startOutput(aps:AudioPolicyService)
AudioPolicyService----mpPolicyManager->startOutput(mpPolicyManager: AudioPolicyManagerBase)
AudioPolicyManagerBase.cpp----AudioPolicyManagerBase::startOutput
AudioPolicyManagerBase.cpp----AudioPolicyManagerBase::setOutputDevice

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MediaPlaybackService.java----ServiceStub—pause
MediaPlaybackService.java---- MediaPlaybackService—pause
MediaPlaybackService.java---- MultiPlayer—pause
MediaPlayer.java----MediaPlayer—pause
MediaPlayer.java----MediaPlayer—_pause
Android_media_MediaPlayer.cpp----android_media_MediaPlayer_pause
Android_media_MediaPlayer.cpp----mp->pause
MediaPlayer.cpp----pause
IMediaPlayer.cpp----pause
IMediaPlayer.cpp----remote()->transact(PAUSE, data, &reply)
IMediaPlayer.cpp----BnMediaPlayer::onTransact
IMediaPlayer.cpp----PAUSE--reply->writeInt32(pause());
MediaPlayerService.cpp----MediaPlayerService::Client::pause()
MediaPlayerService.cpp----MediaPlayerService::AudioOutput::pause()
MediaPlayerService.cpp----mTrack->pause()
AudioFlinger.cpp----AudioFlinger::TrackHandle::pause()
AudioFlinger.cpp----AudioFlinger::PlaybackThread::Track::pause()
AudioFlinger.cpp----AudioSystem::stopOutput
AudioSystem.cpp---- aps->stopOutput
AudioPolicyService----mpPolicyManager->stopOutput
AudioPolicyManagerBase.cpp----AudioPolicyManagerBase::stopOutput
AudioPolicyManagerBase.cpp----AudioPolicyManagerBase::setOutputDevice
从setOutputDevice函数中的代码上分析来看，暂停的过程，stopOutput实际上就是将output的device设置为0.主要的代码摘抄如下：
AudioOutputDescriptor *outputDesc = mOutputs.valueFor(output);
Device=getNewDevice(output);//作为参数传入
outputDesc->mDevice = device;//实际上未执行此句代码

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setParameters—setDeviceConnectionState函数的分析。
AudioSystem.java----AudioServiceBroadcastReceiver---- setDeviceConnectionState
AudioSystem.java----setDeviceConnectionState
Android_media_AudioSystem.cpp---- android_media_AudioSystem_setDeviceConnectionState
Android_media_AudioSystem.cpp---- check_AudioSystem_Command
AudioSystem.cpp---- setDeviceConnectionState
AudioPolicyService.cpp----setDeviceConnectionState
AudioPolicyManagerBase.cpp----setDeviceConnectionState
AudioPolicyManagerBase.cpp----setDeviceConnectionState—setParameters
AudioPolicyManagerBase.cpp----setForceUse—setParameters
AudioPolicyManagerBase.cpp----getOutput—setParameters
AudioPolicyManagerBase.cpp----startInput—setParameters
AudioPolicyManagerBase.cpp----stopInput—setParameters
AudioPolicyManagerBase.cpp---- AudioPolicyManagerBase—setParameters
AudioPolicyManagerBase.cpp---- handleA2dpConnection—setParameters
AudioPolicyManagerBase.cpp---- closeA2dpOutputs—setParameters
AudioPolicyManagerBase.cpp---- setOutputDevice—setParameters
AudioPolicyService.cpp----setParameters
AudioPolicyService.cpp----AudioPolicyService::AudioCommandThread::parametersCommand
AudioPolicyService.cpp----insertCommand_l
AudioPolicyService.cpp----AudioCommandThread::threadLoop--AudioSystem::setParameters
AudioSystem.cpp----setParameters-- af->setParameters
AudioFlinger.cpp----setParameters--mAudioHardware->setParameters
AudioHardwareALSA.h----setParameters--ALSAStreamOps::setParameters
ALSAStreamOps.cpp----setParameters
ALSAStreamOps.cpp----mParent->mALSADevice->route
Alsa_imx5x.cpp----s_route
Alsa_imx5x.cpp----setDefaultControls