audio框架学习-Audio_Flinger分析

之前记录过audioTrack的笔记，这次继续参考audioFlinger相关的代码并做笔记；
参考文档： https://www.cnblogs.com/innost/archive/2011/01/15/1936425.html和 https://blog.csdn.net/zyuanyun/article/details/60890534?spm=1001.2014.3001.5501#t4

一、代码位置

frameworks/av/services/audioflinger/
├── Android.mk
├── AudioFlinger.cpp
├── AudioFlinger.h
├── AudioHwDevice.cpp
├── AudioHwDevice.h
├── AudioMixer.cpp
├── AudioMixer.h
├── AudioMixerOps.h
├── audio-resampler
│   ├── Android.mk
│   ├── AudioResamplerCoefficients.cpp
│   └── filter_coefficients.h
├── AudioResampler.cpp
├── AudioResamplerCubic.cpp
├── AudioResamplerCubic.h
├── AudioResamplerDyn.cpp
├── AudioResamplerDyn.h
├── AudioResamplerFirGen.h
├── AudioResamplerFirOps.h
├── AudioResamplerFirProcess.h
├── AudioResamplerFirProcessNeon.h
├── AudioResampler.h
├── AudioResamplerSinc.cpp
├── AudioResamplerSincDown.h
├── AudioResamplerSinc.h
├── AudioResamplerSincUp.h
├── AudioStreamOut.cpp
├── AudioStreamOut.h
├── AudioWatchdog.cpp
├── AudioWatchdog.h
├── BufferProviders.cpp
├── BufferProviders.h
├── Configuration.h
├── Effects.cpp
├── Effects.h
├── FastCapture.cpp
├── FastCaptureDumpState.cpp
├── FastCaptureDumpState.h
├── FastCapture.h
├── FastCaptureState.cpp
├── FastCaptureState.h
├── FastMixer.cpp
├── FastMixerDumpState.cpp
├── FastMixerDumpState.h
├── FastMixer.h
├── FastMixerState.cpp
├── FastMixerState.h
├── FastThread.cpp
├── FastThreadDumpState.cpp
├── FastThreadDumpState.h
├── FastThread.h
├── FastThreadState.cpp
├── FastThreadState.h
├── MODULE_LICENSE_APACHE2
├── NOTICE
├── PatchPanel.cpp
├── PatchPanel.h
├── PlaybackTracks.h
├── RecordTracks.h
├── ServiceUtilities.cpp
├── ServiceUtilities.h
├── SpdifStreamOut.cpp
├── SpdifStreamOut.h
├── StateQueue.cpp
├── StateQueue.h
├── StateQueueInstantiations.cpp
├── test-resample.cpp
├── tests
│   ├── Android.mk
│   ├── build_and_run_all_unit_tests.sh
│   ├── mixer_to_wav_tests.sh
│   ├── resampler_tests.cpp
│   ├── run_all_unit_tests.sh
│   ├── test-mixer.cpp
│   └── test_utils.h
├── Threads.cpp
├── Threads.h
├── TrackBase.h
└── Tracks.cpp

大概文件讲解：

1. AudioResampler.cpp：重采样处理类，可进行采样率转换和声道转换；由录制线程 AudioFlinger::RecordThread 直接使用
2. AudioMixer.cpp：混音处理类，包括重采样、音量调节、声道转换等，其中的重采样复用了 AudioResampler；由回放线程 AudioFlinger::MixerThread 直接使用
3. Effects.cpp：音效处理类
4. Tracks.cpp：音频流管理类，可控制音频流的状态，如 start、stop、pause
5. Threads.cpp：回放线程和录制线程类；回放线程从 FIFO 读取回放数据并混音处理，然后写数据到输出流设备；录制线程从输入流设备读取录音数据并重采样处理，然后写数据到 FIFO
6. AudioFlinger.cpp：AudioFlinger 对外提供的服务接口
   还有一些相关文件不再这目录下，但是基本都在frameworks这个目录下，所以到时候只需要找一找就行。

二、audio服务启动

2.1 main服务

万事皆有一个开始，audio的也是，他也有一个服务启动代码，启动对应的服务。
代码位置：frameworks/av/media/audioserver/main_audioserver.cpp
这个里面就一个main函数，主要就是用于启动各种相关服务。

        if (doLog) {
            prctl(PR_SET_PDEATHSIG, SIGKILL);   // if parent media.log dies before me, kill me also
            setpgid(0, 0);                      // but if I die first, don't kill my parent
        }
        android::hardware::configureRpcThreadpool(4, false /*callerWillJoin*/);
        sp<ProcessState> proc(ProcessState::self());
        sp<IServiceManager> sm = defaultServiceManager();
        ALOGI("ServiceManager: %p", sm.get());
        /*加载AudioFlinger的服务*/
        AudioFlinger::instantiate();
        /*加载AudioPolicyService的服务*/
        AudioPolicyService::instantiate();

        // AAudioService should only be used in OC-MR1 and later.
        // And only enable the AAudioService if the system MMAP policy explicitly allows it.
        // This prevents a client from misusing AAudioService when it is not supported.
        aaudio_policy_t mmapPolicy = property_get_int32(AAUDIO_PROP_MMAP_POLICY,
                                                        AAUDIO_POLICY_NEVER);
        if (mmapPolicy == AAUDIO_POLICY_AUTO || mmapPolicy == AAUDIO_POLICY_ALWAYS) {
            AAudioService::instantiate();
        }

        SoundTriggerHwService::instantiate();
        ProcessState::self()->startThreadPool();
        IPCThreadState::self()->joinThreadPool();
    }

2.2 audioflinger添加到系统服务中

framework/base/libs/audioFlinger/audioFlinger.cpp

static sp<os::IExternalVibratorService> getExternalVibratorService() {
    if (sExternalVibratorService == 0) {
    	/*把audioflinger添加到服务中去*/
        sp <IBinder> binder = defaultServiceManager()->getService(
            String16("external_vibrator_service"));
        if (binder != 0) {
            sExternalVibratorService =
                interface_cast<os::IExternalVibratorService>(binder);
        }
    }
    return sExternalVibratorService;
}

audio的构造函数

AudioFlinger::AudioFlinger()
    : BnAudioFlinger(),//初始化基类
      mMediaLogNotifier(new AudioFlinger::MediaLogNotifier()),
      mPrimaryHardwareDev(NULL),
      mAudioHwDevs(NULL),
      /*创建代表Audio硬件的HAL对象*/
      mHardwareStatus(AUDIO_HW_IDLE),
      mMasterVolume(1.0f),
      mMasterMute(false),
      // mNextUniqueId(AUDIO_UNIQUE_ID_USE_MAX),
      mMode(AUDIO_MODE_INVALID),
      mBtNrecIsOff(false),
      mIsLowRamDevice(true),
      mIsDeviceTypeKnown(false),
      mTotalMemory(0),
      mClientSharedHeapSize(kMinimumClientSharedHeapSizeBytes),
      mGlobalEffectEnableTime(0),
      mPatchPanel(this),
      mSystemReady(false)
{
    // unsigned instead of audio_unique_id_use_t, because ++ operator is unavailable for enum
    for (unsigned use = AUDIO_UNIQUE_ID_USE_UNSPECIFIED; use < AUDIO_UNIQUE_ID_USE_MAX; use++) {
        // zero ID has a special meaning, so unavailable
        mNextUniqueIds[use] = AUDIO_UNIQUE_ID_USE_MAX;
    }

    const bool doLog = property_get_bool("ro.test_harness", false);
    if (doLog) {
        mLogMemoryDealer = new MemoryDealer(kLogMemorySize, "LogWriters",
                MemoryHeapBase::READ_ONLY);
        (void) pthread_once(&sMediaLogOnce, sMediaLogInit);
    }

    // reset battery stats.
    // if the audio service has crashed, battery stats could be left
    // in bad state, reset the state upon service start.
    BatteryNotifier::getInstance().noteResetAudio();

    mDevicesFactoryHal = DevicesFactoryHalInterface::create();
    mEffectsFactoryHal = EffectsFactoryHalInterface::create();

    mMediaLogNotifier->run("MediaLogNotifier");
}

audio还可以设置对应的硬件模式

status_t AudioFlinger::setMode(audio_mode_t mode)
{
    status_t ret = initCheck();
    if (ret != NO_ERROR) {
        return ret;
    }

    // check calling permissions
    if (!settingsAllowed()) {
        return PERMISSION_DENIED;
    }
    if (uint32_t(mode) >= AUDIO_MODE_CNT) {
        ALOGW("Illegal value: setMode(%d)", mode);
        return BAD_VALUE;
    }

    { // scope for the lock
        AutoMutex lock(mHardwareLock);
        sp<DeviceHalInterface> dev = mPrimaryHardwareDev->hwDevice();
        mHardwareStatus = AUDIO_HW_SET_MODE;
        ret = dev->setMode(mode);
        mHardwareStatus = AUDIO_HW_IDLE;
    }

    if (NO_ERROR == ret) {
        Mutex::Autolock _l(mLock);
        mMode = mode;
        for (size_t i = 0; i < mPlaybackThreads.size(); i++)
            mPlaybackThreads.valueAt(i)->setMode(mode);
    }

    return ret;
}

2.3 audioflinger的服务接口

Interface	Description
sampleRate	获取硬件设备的采样率
format	获取硬件设备的音频格式
frameCount	获取硬件设备的周期帧数
latency	获取硬件设备的传输延迟
setMasterVolume	调节主输出设备的音量
setMasterMute	静音主输出设备
setStreamVolume	调节指定类型的音频流的音量，这种调节不影响其他类型的音频流的音量
setStreamMute	静音指定类型的音频流
setVoiceVolume	调节通话音量
setMicMute	静音麦克风输入
setMode	切换音频模式：音频模式有 4 种，分别是 Normal、Ringtone、Call、Communicatoin
setParameters	设置音频参数：往下调用 HAL 层相应接口，常用于切换音频通道
getParameters	获取音频参数：往下调用 HAL 层相应接口
openOutput	打开输出流：打开输出流设备，并创建 PlaybackThread 对象
closeOutput	关闭输出流：移除并销毁 PlaybackThread 上面挂着的所有的 Track，退出 PlaybackThread，关闭输出流设备
openInput	打开输入流：打开输入流设备，并创建 RecordThread 对象
closeInput	关闭输入流：退出 RecordThread，关闭输入流设备
createTrack	新建输出流管理对象： 找到对应的 PlaybackThread，创建输出流管理对象 Track，然后创建并返回该 Track 的代理对象 TrackHandle
openRecord	新建输入流管理对象：找到 RecordThread，创建输入流管理对象 RecordTrack，然后创建并返回该 RecordTrack 的代理对象 RecordHandle

1. 获取硬件设备的配置信息
2. 音量调节
3. 静音操作
4. 音频模式切换
5. 音频参数设置
6. 输入输出流设备管理
7. 音频流管理

AudioFlinger 服务启动后，其他进程可以通过 ServiceManager 来获取其代理对象 IAudioFlinger，通过 IAudioFlinger 可以向 AudioFlinger 发出各种服务请求，从而完成自己的音频业务。