Android8.0 Audio系统之硬件抽象层

游戏硬件与操作系统兼容性很重要 #生活乐趣# #游戏乐趣# #游戏硬件#

经过以上三篇对AudioTrack，AudioFlinger, AudioPolicy的分析，发现音频数据经过AudioTrack，通过AudioPolicy路由，由AudioFlinger的各路线程混合输出到合适的Audio设备去。我们再分析AudioFlinger构造函数的时候涉及到音频硬件抽象层但是没有深入研究，现在，我们回过头来继续看看。

1. Audio系统设备抽象

AudioFlinger::AudioFlinger() : BnAudioFlinger(), ...... { ...... mDevicesFactoryHal = DevicesFactoryHalInterface::create(); //硬件抽象 mEffectsFactoryHal = EffectsFactoryHalInterface::create(); } 12345678

DevicesFactoryHalHybrid类将持有DevicesFactoryHalInterface的两个实现

class DevicesFactoryHalHybrid : public DevicesFactoryHalInterface { public: // Opens a device with the specified name. To close the device, it is // necessary to release references to the returned object. virtual status_t openDevice(const char *name, sp<DeviceHalInterface> *device); private: friend class DevicesFactoryHalInterface; // Can not be constructed directly by clients. DevicesFactoryHalHybrid(); virtual ~DevicesFactoryHalHybrid(); sp<DevicesFactoryHalInterface> mLocalFactory; sp<DevicesFactoryHalInterface> mHidlFactory; };

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具体实现如下，通过系统的宏编译控制创建新老版本的硬件抽象层

sp<DevicesFactoryHalInterface> DevicesFactoryHalInterface::create() { return new DevicesFactoryHalHybrid(); } DevicesFactoryHalHybrid::DevicesFactoryHalHybrid() : mLocalFactory(new DevicesFactoryHalLocal()), mHidlFactory( #ifdef USE_LEGACY_LOCAL_AUDIO_HAL nullptr #else new DevicesFactoryHalHidl() #endif ) { } DevicesFactoryHalHybrid::~DevicesFactoryHalHybrid() { } //AudioFlinger中调用 status_t DevicesFactoryHalHybrid::openDevice(const char *name, sp<DeviceHalInterface> *device) { if (mHidlFactory != 0 && strcmp(AUDIO_HARDWARE_MODULE_ID_A2DP, name) != 0) { return mHidlFactory->openDevice(name, device); //Trable架构 } return mLocalFactory->openDevice(name, device); //hardware架构 }

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在AudioPolicyService构造函数中，根据Audio配置文件载入Audio设备模块，具体函数在AudioFlinger中

audio_module_handle_t AudioFlinger::loadHwModule_l(const char *name) { int rc = mDevicesFactoryHal->openDevice(name, &dev); //打开具体的Device mAudioHwDevs.add(handle, new AudioHwDevice(handle, name, dev, flags)); //抽象为AudioHwDevice return handle; } 12345678910

如果调用 mLocalFactory->openDevice(name, device); //hardware架构，将以8.0以前的模式加载音频模块

static status_t load_audio_interface(const char *if_name, audio_hw_device_t **dev) { const hw_module_t *mod; int rc; rc = hw_get_module_by_class(AUDIO_HARDWARE_MODULE_ID, if_name, &mod); if (rc) { ALOGE("%s couldn't load audio hw module %s.%s (%s)", __func__, AUDIO_HARDWARE_MODULE_ID, if_name, strerror(-rc)); goto out; } rc = audio_hw_device_open(mod, dev); if (rc) { ALOGE("%s couldn't open audio hw device in %s.%s (%s)", __func__, AUDIO_HARDWARE_MODULE_ID, if_name, strerror(-rc)); goto out; } if ((*dev)->common.version < AUDIO_DEVICE_API_VERSION_MIN) { ALOGE("%s wrong audio hw device version %04x", __func__, (*dev)->common.version); rc = BAD_VALUE; audio_hw_device_close(*dev); goto out; } return OK; out: *dev = NULL; return rc; } status_t DevicesFactoryHalLocal::openDevice(const char *name, sp<DeviceHalInterface> *device) { audio_hw_device_t *dev; status_t rc = load_audio_interface(name, &dev); if (rc == OK) { *device = new DeviceHalLocal(dev); //封装为DeviceHalLocal } return rc; }

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如果调用 mHidlFactory->openDevice(name, device); //Trable架构

DevicesFactoryHalHidl::DevicesFactoryHalHidl() { mDevicesFactory = IDevicesFactory::getService(); //将调用Treble架构下的HW if (mDevicesFactory != 0) { // It is assumed that DevicesFactory is owned by AudioFlinger // and thus have the same lifespan. mDevicesFactory->linkToDeath(HalDeathHandler::getInstance(), 0 /*cookie*/); } else { ALOGE("Failed to obtain IDevicesFactory service, terminating process."); exit(1); } } DevicesFactoryHalHidl::~DevicesFactoryHalHidl() { } // static status_t DevicesFactoryHalHidl::nameFromHal(const char *name, IDevicesFactory::Device *device) { if (strcmp(name, AUDIO_HARDWARE_MODULE_ID_PRIMARY) == 0) { *device = IDevicesFactory::Device::PRIMARY; return OK; } else if(strcmp(name, AUDIO_HARDWARE_MODULE_ID_A2DP) == 0) { *device = IDevicesFactory::Device::A2DP; return OK; } else if(strcmp(name, AUDIO_HARDWARE_MODULE_ID_USB) == 0) { *device = IDevicesFactory::Device::USB; return OK; } else if(strcmp(name, AUDIO_HARDWARE_MODULE_ID_REMOTE_SUBMIX) == 0) { *device = IDevicesFactory::Device::R_SUBMIX; return OK; } else if(strcmp(name, AUDIO_HARDWARE_MODULE_ID_STUB) == 0) { *device = IDevicesFactory::Device::STUB; return OK; } ALOGE("Invalid device name %s", name); return BAD_VALUE; } status_t DevicesFactoryHalHidl::openDevice(const char *name, sp<DeviceHalInterface> *device) { if (mDevicesFactory == 0) return NO_INIT; IDevicesFactory::Device hidlDevice; status_t status = nameFromHal(name, &hidlDevice); if (status != OK) return status; Result retval = Result::NOT_INITIALIZED; Return<void> ret = mDevicesFactory->openDevice( //调用加载具体的Device hidlDevice, [&](Result r, const sp<IDevice>& result) { retval = r; if (retval == Result::OK) { *device = new DeviceHalHidl(result); //封装为DeviceHalHidl } }); if (ret.isOk()) { if (retval == Result::OK) return OK; else if (retval == Result::INVALID_ARGUMENTS) return BAD_VALUE; else return NO_INIT; } return FAILED_TRANSACTION; }

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hardware\interfaces\audio\2.0\default\DevicesFactory.h

struct DevicesFactory : public IDevicesFactory { // Methods from ::android::hardware::audio::V2_0::IDevicesFactory follow. Return<void> openDevice(IDevicesFactory::Device device, openDevice_cb _hidl_cb) override; private: static const char* deviceToString(IDevicesFactory::Device device); static int loadAudioInterface(const char *if_name, audio_hw_device_t **dev); }; extern "C" IDevicesFactory* HIDL_FETCH_IDevicesFactory(const char* name); 1234567891011

hardware\interfaces\audio\2.0\default\DevicesFactory.cpp

// Methods from ::android::hardware::audio::V2_0::IDevicesFactory follow. Return<void> DevicesFactory::openDevice(IDevicesFactory::Device device, openDevice_cb _hidl_cb) { audio_hw_device_t *halDevice; Result retval(Result::INVALID_ARGUMENTS); sp<IDevice> result; const char* moduleName = deviceToString(device); if (moduleName != nullptr) { int halStatus = loadAudioInterface(moduleName, &halDevice); //加载音频模块设备 if (halStatus == OK) { if (device == IDevicesFactory::Device::PRIMARY) { result = new PrimaryDevice(halDevice); } else { result = new ::android::hardware::audio::V2_0::implementation:: Device(halDevice); } retval = Result::OK; } else if (halStatus == -EINVAL) { retval = Result::NOT_INITIALIZED; } } _hidl_cb(retval, result); return Void(); } IDevicesFactory* HIDL_FETCH_IDevicesFactory(const char* /* name */) { return new DevicesFactory(); }

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加载具体的音频模块设备

// static int DevicesFactory::loadAudioInterface(const char *if_name, audio_hw_device_t **dev) { const hw_module_t *mod; int rc; rc = hw_get_module_by_class(AUDIO_HARDWARE_MODULE_ID, if_name, &mod); if (rc) { ALOGE("%s couldn't load audio hw module %s.%s (%s)", __func__, AUDIO_HARDWARE_MODULE_ID, if_name, strerror(-rc)); goto out; } rc = audio_hw_device_open(mod, dev); if (rc) { ALOGE("%s couldn't open audio hw device in %s.%s (%s)", __func__, AUDIO_HARDWARE_MODULE_ID, if_name, strerror(-rc)); goto out; } if ((*dev)->common.version < AUDIO_DEVICE_API_VERSION_MIN) { ALOGE("%s wrong audio hw device version %04x", __func__, (*dev)->common.version); rc = -EINVAL; audio_hw_device_close(*dev); goto out; } return OK; out: *dev = NULL; return rc; }

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在service.cpp文件中我们看到Treble架构下的几项注册到hwservicemanager的服务包括 IDevicesFactory，IEffectsFactory， ISoundTriggerHw， IBroadcastRadioFactory几项

hardware\interfaces\audio\2.0\default\service.cpp

int main(int /* argc */, char* /* argv */ []) { configureRpcThreadpool(16, true /*callerWillJoin*/); android::status_t status; status = registerPassthroughServiceImplementation<IDevicesFactory>(); LOG_ALWAYS_FATAL_IF(status != OK, "Error while registering audio service: %d", status); status = registerPassthroughServiceImplementation<IEffectsFactory>(); LOG_ALWAYS_FATAL_IF(status != OK, "Error while registering audio effects service: %d", status); // Soundtrigger and FM radio might be not present. status = registerPassthroughServiceImplementation<ISoundTriggerHw>(); ALOGE_IF(status != OK, "Error while registering soundtrigger service: %d", status); if (useBroadcastRadioFutureFeatures) { status = registerPassthroughServiceImplementation< broadcastradio::V1_1::IBroadcastRadioFactory>(); } else { status = registerPassthroughServiceImplementation< broadcastradio::V1_0::IBroadcastRadioFactory>(); } ALOGE_IF(status != OK, "Error while registering fm radio service: %d", status); joinRpcThreadpool(); return status; }

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2. Audio系统硬件抽象层

再看 DeviceHalLocal，实现自DeviceHalInterface

DeviceHalLocal::DeviceHalLocal(audio_hw_device_t *dev) : mDev(dev) { } ...... status_t DeviceHalLocal::openOutputStream( audio_io_handle_t handle, audio_devices_t devices, audio_output_flags_t flags, struct audio_config *config, const char *address, sp<StreamOutHalInterface> *outStream) { audio_stream_out_t *halStream; ALOGV("open_output_stream handle: %d devices: %x flags: %#x" "srate: %d format %#x channels %x address %s", handle, devices, flags, config->sample_rate, config->format, config->channel_mask, address); int openResut = mDev->open_output_stream( mDev, handle, devices, flags, config, &halStream, address); if (openResut == OK) { *outStream = new StreamOutHalLocal(halStream, this); } ALOGV("open_output_stream status %d stream %p", openResut, halStream); return openResut; } ......

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调用硬件抽象层的音频流输出函数

static int adev_open_output_stream(struct audio_hw_device *dev, audio_io_handle_t handle, audio_devices_t devices, audio_output_flags_t flags, struct audio_config *config, struct audio_stream_out **stream_out, const char *address __unused) { ALOGV("adev_open_output_stream..."); *stream_out = NULL; struct stub_stream_out *out = (struct stub_stream_out *)calloc(1, sizeof(struct stub_stream_out)); if (!out) return -ENOMEM; out->stream.common.get_sample_rate = out_get_sample_rate; out->stream.common.set_sample_rate = out_set_sample_rate; out->stream.common.get_buffer_size = out_get_buffer_size; out->stream.common.get_channels = out_get_channels; out->stream.common.get_format = out_get_format; out->stream.common.set_format = out_set_format; out->stream.common.standby = out_standby; out->stream.common.dump = out_dump; out->stream.common.set_parameters = out_set_parameters; out->stream.common.get_parameters = out_get_parameters; out->stream.common.add_audio_effect = out_add_audio_effect; out->stream.common.remove_audio_effect = out_remove_audio_effect; out->stream.get_latency = out_get_latency; out->stream.set_volume = out_set_volume; out->stream.write = out_write; out->stream.get_render_position = out_get_render_position; out->stream.get_next_write_timestamp = out_get_next_write_timestamp; *stream_out = &out->stream; return 0; }

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DeviceHalHidl 实现自 DeviceHalInterface

status_t DeviceHalHidl::openOutputStream( audio_io_handle_t handle, audio_devices_t devices, audio_output_flags_t flags, struct audio_config *config, const char *address, sp<StreamOutHalInterface> *outStream) { if (mDevice == 0) return NO_INIT; DeviceAddress hidlDevice; status_t status = deviceAddressFromHal(devices, address, &hidlDevice); if (status != OK) return status; AudioConfig hidlConfig; HidlUtils::audioConfigFromHal(*config, &hidlConfig); Result retval = Result::NOT_INITIALIZED; Return<void> ret = mDevice->openOutputStream( //输出Audio流， 调用硬件抽象层的音频流输出函数 handle, hidlDevice, hidlConfig, AudioOutputFlag(flags), [&](Result r, const sp<IStreamOut>& result, const AudioConfig& suggestedConfig) { retval = r; if (retval == Result::OK) { *outStream = new StreamOutHalHidl(result); } HidlUtils::audioConfigToHal(suggestedConfig, config); }); return processReturn("openOutputStream", ret, retval); }

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至此整个Audio系统的分析到此结束，其实Audio系统还有很大一部分，在整个Android系统中错综复杂，实在难以详述，只能摘其精要，略其枝蔓。下一个专题我们要来啃一啃Media系统，作为Android重要且复杂的系统来分析，可能会有漫长的篇幅。

网址：Android8.0 Audio系统之硬件抽象层 https://www.yuejiaxmz.com/news/view/242120

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