版权声明：未经本人同意，不得转载 https://blog.csdn.net/u013928208/article/details/81660347
上一篇我们跟踪分析了AudioFlinger，它是Audio系统的核心，但是AudioFlinger却不能脱离AudioPolicy工作。AudioPolicy模块承载着音频切换，音轨路由的重要工作，没有它，音频输出将乱套。在分析AudioFlinger的时候我们稍微涉及了AudioPolicyService，现在我们重新来看它。在Android7.0中Audio代理部分被组成独立的模块。
void AudioPolicyService::onFirstRef()
{
{
......
// class AudioPolicyClient : public AudioPolicyClientInterface
mAudioPolicyClient = new AudioPolicyClient(this);
mAudioPolicyManager = createAudioPolicyManager(mAudioPolicyClient); //创建Audio管理
}
}头文件 AudioPolicyClientInterface 位于 AudioPolicyInterface.h文件中
extern "C" AudioPolicyInterface* createAudioPolicyManager(
AudioPolicyClientInterface *clientInterface)
{
return new AudioPolicyManager(clientInterface);
}
extern "C" void destroyAudioPolicyManager(AudioPolicyInterface *interface)
{
delete interface;
}对于AudioPolicyClientImpl.cpp实现了 AudioPolicyClient，直接与AudioFlinger交互。对于AudioPolicyIntefaceImpl实现了AudioPolicyInterface直接与AudioPolicyManager交互，
AudioPolicyManager::AudioPolicyManager(AudioPolicyClientInterface *clientInterface)
:
#ifdef AUDIO_POLICY_TEST
Thread(false),
#endif //AUDIO_POLICY_TEST
mLimitRingtoneVolume(false), mLastVoiceVolume(-1.0f),
mA2dpSuspended(false),
mAudioPortGeneration(1),
mBeaconMuteRefCount(0),
mBeaconPlayingRefCount(0),
mBeaconMuted(false),
mTtsOutputAvailable(false),
mMasterMono(false),
mMusicEffectOutput(AUDIO_IO_HANDLE_NONE)
{
mpClientInterface = clientInterface;
bool speakerDrcEnabled = false;
//解析 xml Audio策略，路由
#ifdef USE_XML_AUDIO_POLICY_CONF
mVolumeCurves = new VolumeCurvesCollection();
AudioPolicyConfig config(mHwModules, mAvailableOutputDevices, mAvailableInputDevices,
mDefaultOutputDevice, speakerDrcEnabled,
static_cast<VolumeCurvesCollection *>(mVolumeCurves));
if (deserializeAudioPolicyXmlConfig(config) != NO_ERROR) {
#else
mVolumeCurves = new StreamDescriptorCollection();
AudioPolicyConfig config(mHwModules, mAvailableOutputDevices, mAvailableInputDevices,
mDefaultOutputDevice, speakerDrcEnabled);
if ((ConfigParsingUtils::loadConfig(AUDIO_POLICY_VENDOR_CONFIG_FILE, config) != NO_ERROR) &&
(ConfigParsingUtils::loadConfig(AUDIO_POLICY_CONFIG_FILE, config) != NO_ERROR)) {
#endif
ALOGE("could not load audio policy configuration file, setting defaults");
config.setDefault();
}
// must be done after reading the policy (since conditionned by Speaker Drc Enabling)
mVolumeCurves->initializeVolumeCurves(speakerDrcEnabled);
// Once policy config has been parsed, retrieve an instance of the engine and initialize it
//代理引擎
audio_policy::EngineInstance *engineInstance = audio_policy::EngineInstance::getInstance();
if (!engineInstance) {
ALOGE("%s: Could not get an instance of policy engine", __FUNCTION__);
return;
}
// Retrieve the Policy Manager Interface
mEngine = engineInstance->queryInterface<AudioPolicyManagerInterface>(); //获取引擎
mEngine->setObserver(this); //设为观察者
status_t status = mEngine->initCheck(); //初始
(void) status;
// mAvailableOutputDevices and mAvailableInputDevices now contain all attached devices
// open all output streams needed to access attached devices
audio_devices_t outputDeviceTypes = mAvailableOutputDevices.types();
audio_devices_t inputDeviceTypes = mAvailableInputDevices.types() & ~AUDIO_DEVICE_BIT_IN;
for (size_t i = 0; i < mHwModules.size(); i++) {
//调用ClientInterface加载Audio模块，ClientInterface将调用AudioFlinger的loadHwModule
mHwModules[i]->mHandle = mpClientInterface->loadHwModule(mHwModules[i]->getName());
if (mHwModules[i]->mHandle == 0) {
ALOGW("could not open HW module %s", mHwModules[i]->getName());
continue;
}
//查找输出模块设备
for (size_t j = 0; j < mHwModules[i]->mOutputProfiles.size(); j++)
{
const sp<IOProfile> outProfile = mHwModules[i]->mOutputProfiles[j];
if (!outProfile->hasSupportedDevices()) {
ALOGW("Output profile contains no device on module %s", mHwModules[i]->getName());
continue;
}
if ((outProfile->getFlags() & AUDIO_OUTPUT_FLAG_TTS) != 0) {
mTtsOutputAvailable = true;
}
if ((outProfile->getFlags() & AUDIO_OUTPUT_FLAG_DIRECT) != 0) {
continue;
}
audio_devices_t profileType = outProfile->getSupportedDevicesType();
if ((profileType & mDefaultOutputDevice->type()) != AUDIO_DEVICE_NONE) {
profileType = mDefaultOutputDevice->type();
} else {
profileType = outProfile->getSupportedDeviceForType(outputDeviceTypes);
}
if ((profileType & outputDeviceTypes) == 0) {
continue;
}
sp<SwAudioOutputDescriptor> outputDesc = new SwAudioOutputDescriptor(outProfile,
mpClientInterface);
const DeviceVector &supportedDevices = outProfile->getSupportedDevices();
const DeviceVector &devicesForType = supportedDevices.getDevicesFromType(profileType);
String8 address = devicesForType.size() > 0 ? devicesForType.itemAt(0)->mAddress
: String8("");
outputDesc->mDevice = profileType;
audio_config_t config = AUDIO_CONFIG_INITIALIZER;
config.sample_rate = outputDesc->mSamplingRate;
config.channel_mask = outputDesc->mChannelMask;
config.format = outputDesc->mFormat;
audio_io_handle_t output = AUDIO_IO_HANDLE_NONE;
//熟悉的openOutput
status_t status = mpClientInterface->openOutput(outProfile->getModuleHandle(),
&output,
&config,
&outputDesc->mDevice,
address,
&outputDesc->mLatency,
outputDesc->mFlags);
if (status != NO_ERROR) {
ALOGW("Cannot open output stream for device %08x on hw module %s",
outputDesc->mDevice,
mHwModules[i]->getName());
} else {
outputDesc->mSamplingRate = config.sample_rate;
outputDesc->mChannelMask = config.channel_mask;
outputDesc->mFormat = config.format;
for (size_t k = 0; k < supportedDevices.size(); k++) {
ssize_t index = mAvailableOutputDevices.indexOf(supportedDevices[k]);
// give a valid ID to an attached device once confirmed it is reachable
if (index >= 0 && !mAvailableOutputDevices[index]->isAttached()) {
mAvailableOutputDevices[index]->attach(mHwModules[i]);
}
}
if (mPrimaryOutput == 0 &&
outProfile->getFlags() & AUDIO_OUTPUT_FLAG_PRIMARY) {
mPrimaryOutput = outputDesc;
}
addOutput(output, outputDesc);
setOutputDevice(outputDesc,
outputDesc->mDevice,
true,
0,
NULL,
address.string());
}
}
//遍历输入Audio设备
for (size_t j = 0; j < mHwModules[i]->mInputProfiles.size(); j++)
{
const sp<IOProfile> inProfile = mHwModules[i]->mInputProfiles[j];
if (!inProfile->hasSupportedDevices()) {
ALOGW("Input profile contains no device on module %s", mHwModules[i]->getName());
continue;
}
// chose first device present in profile's SupportedDevices also part of
// inputDeviceTypes
audio_devices_t profileType = inProfile->getSupportedDeviceForType(inputDeviceTypes);
if ((profileType & inputDeviceTypes) == 0) {
continue;
}
sp<AudioInputDescriptor> inputDesc =
new AudioInputDescriptor(inProfile);
inputDesc->mDevice = profileType;
......
audio_config_t config = AUDIO_CONFIG_INITIALIZER;
config.sample_rate = inputDesc->mSamplingRate;
config.channel_mask = inputDesc->mChannelMask;
config.format = inputDesc->mFormat;
audio_io_handle_t input = AUDIO_IO_HANDLE_NONE;
status_t status = mpClientInterface->openInput(inProfile->getModuleHandle(),
&input,
&config,
&inputDesc->mDevice,
address,
AUDIO_SOURCE_MIC,
AUDIO_INPUT_FLAG_NONE);
if (status == NO_ERROR) {
const DeviceVector &supportedDevices = inProfile->getSupportedDevices();
for (size_t k = 0; k < supportedDevices.size(); k++) {
ssize_t index = mAvailableInputDevices.indexOf(supportedDevices[k]);
// give a valid ID to an attached device once confirmed it is reachable
if (index >= 0) {
sp<DeviceDescriptor> devDesc = mAvailableInputDevices[index];
if (!devDesc->isAttached()) {
devDesc->attach(mHwModules[i]);
devDesc->importAudioPort(inProfile);
}
}
}
mpClientInterface->closeInput(input);
}
}
}
// make sure all attached devices have been allocated a unique ID
//遍历输入输出设备，由路由引擎设置各设备的连接状态
for (size_t i = 0; i < mAvailableOutputDevices.size();) {
if (!mAvailableOutputDevices[i]->isAttached()) {
mAvailableOutputDevices.remove(mAvailableOutputDevices[i]);
continue;
}
// The device is now validated and can be appended to the available devices of the engine
mEngine->setDeviceConnectionState(mAvailableOutputDevices[i],
AUDIO_POLICY_DEVICE_STATE_AVAILABLE);
i++;
}
for (size_t i = 0; i < mAvailableInputDevices.size();) {
if (!mAvailableInputDevices[i]->isAttached()) ;
mAvailableInputDevices.remove(mAvailableInputDevices[i]);
continue;
}
// The device is now validated and can be appended to the available devices of the engine
mEngine->setDeviceConnectionState(mAvailableInputDevices[i],
AUDIO_POLICY_DEVICE_STATE_AVAILABLE);
i++;
}
updateDevicesAndOutputs();
}可以看到AudioPolicyManager通过解析Audio配置文件，加载各输入输出音频Module，然后遍历各输入输出设备，找出稳定的设备后，由路由引擎设置各设备的连接状态。在分析AudioFlinger的时候走过 mpClientInterface->openOutput()函数
sp<AudioFlinger::ThreadBase> AudioFlinger::openOutput_l(.....)
{
//找到Device, 这个函数很重要，稍后分析
AudioHwDevice *outHwDev = findSuitableHwDev_l(module, devices);
//音频流输出到硬件设备
AudioStreamOut *outputStream = NULL;
status_t status = outHwDev->openOutputStream(
&outputStream,
*output,
devices,
flags,
config,
address.string());
mHardwareStatus = AUDIO_HW_IDLE;在 createTrack_l()的时候，会去根据流类型来获取路由策略
uint32_t strategy = AudioSystem::getStrategyForStream(streamType);
for (size_t i = 0; i < mTracks.size(); ++i) {
sp<Track> t = mTracks[i];
if (t != 0 && t->isExternalTrack()) {
//获取路由策略
uint32_t actual = AudioSystem::getStrategyForStream(t->streamType());
if (sessionId == t->sessionId() && strategy != actual) {
ALOGE("createTrack_l() mismatched strategy; expected %u but found %u",
strategy, actual);
lStatus = BAD_VALUE;
goto Exit;
}
}
}调用 Audio代理服务的 getStrategyForStream
uint32_t AudioSystem::getStrategyForStream(audio_stream_type_t stream)
{
const sp<IAudioPolicyService>& aps = AudioSystem::get_audio_policy_service();
if (aps == 0) return 0;
return aps->getStrategyForStream(stream);
}具体的实现在AudioPolicyInterfaceImpl.cpp文件中
\frameworks\av\services\audiopolicy\service\AudioPolicyInterfaceImpl.cpp
uint32_t AudioPolicyService::getStrategyForStream(audio_stream_type_t stream)
{
if (uint32_t(stream) >= AUDIO_STREAM_PUBLIC_CNT) {
return 0;
}
if (mAudioPolicyManager == NULL) {
return 0;
}
return mAudioPolicyManager->getStrategyForStream(stream);
}uint32_t AudioPolicyManager::getStrategyForStream(audio_stream_type_t stream) {
return (uint32_t)getStrategy(stream);
}routing_strategy AudioPolicyManager::getStrategy(audio_stream_type_t stream) const
{
ALOG_ASSERT(stream != AUDIO_STREAM_PATCH,"getStrategy() called for AUDIO_STREAM_PATCH");
return mEngine->getStrategyForStream(stream);
}
在文件 frameworks\av\services\audiopolicy\managerdefault\AudioPolicyManager.h 中 AudioPolicyManagerInterface *mEngine; 位于frameworks\av\services\audiopolicy\engine\interface\AudioPolicyManagerInterface.h，在frameworks\av\services\audiopolicy\enginedefault\src\Engine.h文件中被实现如下
/// Interface members
class ManagerInterfaceImpl : public AudioPolicyManagerInterface
{
public:
explicit ManagerInterfaceImpl(Engine *policyEngine)
: mPolicyEngine(policyEngine) {}
......
virtual routing_strategy getStrategyForStream(audio_stream_type_t stream)
{
return mPolicyEngine->getStrategyForStream(stream);
}
......
private:
Engine *mPolicyEngine;
} mManagerInterface;最终将调用Engine.cpp的getStrategyForStream查询音频路由策略
routing_strategy Engine::getStrategyForStream(audio_stream_type_t stream)
{
// stream to strategy mapping
switch (stream) {
case AUDIO_STREAM_VOICE_CALL:
case AUDIO_STREAM_BLUETOOTH_SCO:
return STRATEGY_PHONE;
case AUDIO_STREAM_RING:
case AUDIO_STREAM_ALARM:
return STRATEGY_SONIFICATION;
case AUDIO_STREAM_NOTIFICATION:
return STRATEGY_SONIFICATION_RESPECTFUL;
case AUDIO_STREAM_DTMF:
return STRATEGY_DTMF;
default:
ALOGE("unknown stream type %d", stream);
case AUDIO_STREAM_SYSTEM:
// NOTE: SYSTEM stream uses MEDIA strategy because muting music and switching outputs
// while key clicks are played produces a poor result
case AUDIO_STREAM_MUSIC:
return STRATEGY_MEDIA;
case AUDIO_STREAM_ENFORCED_AUDIBLE:
return STRATEGY_ENFORCED_AUDIBLE;
case AUDIO_STREAM_TTS:
return STRATEGY_TRANSMITTED_THROUGH_SPEAKER;
case AUDIO_STREAM_ACCESSIBILITY:
return STRATEGY_ACCESSIBILITY;
case AUDIO_STREAM_REROUTING:
return STRATEGY_REROUTING;
}
}在AudioPolicyService.h文件中定义了如下函数，用来处理设备改变时调整路由策略
virtual status_t handleDeviceConfigChange(audio_devices_t device,
const char *device_address,
const char *device_name);至此音频代理路由部分暂到这，目前所看到的只是一小部分，随着Android系统的日益复杂，Audio会变得越来越庞大；
不过万变不离其宗，只要大体架构上不做大改动，也是很容易分析的，下一篇我们来看Audio系统的硬件抽象层。