【0006】Android音频设备解析
【1】函数loadHwModule_l解析
1
2 // loadHwModule_l() must be called with AudioFlinger::mLock held
3 audio_module_handle_t AudioFlinger::loadHwModule_l(const char *name)
4 {
5 //【1】判断是否添加interface?
6 for (size_t i = 0; i < mAudioHwDevs.size(); i++) {
7 if (strncmp(mAudioHwDevs.valueAt(i)->moduleName(), name, strlen(name)) == 0) {
8 ALOGW("loadHwModule() module %s already loaded", name);
9 return mAudioHwDevs.keyAt(i);
10 }
11 }
12
13 audio_hw_device_t *dev;
14 //【2】加载audio interface
15 int rc = load_audio_interface(name, &dev);
16 if (rc) {
17 ALOGI("loadHwModule() error %d loading module %s ", rc, name);
18 return 0;
19 }
20 //【3】初始化
21 mHardwareStatus = AUDIO_HW_INIT;
22 rc = dev->init_check(dev);
23 //每次初始化都需要改变mHardwareStatus的值，为了正确dump出输出内部状态；
24 mHardwareStatus = AUDIO_HW_IDLE;
25 if (rc) {
26 ALOGI("loadHwModule() init check error %d for module %s ", rc, name);
27 return 0;
28 }
29
30 // Check and cache this HAL's level of support for master mute and master
31 // volume. If this is the first HAL opened, and it supports the get
32 // methods, use the initial values provided by the HAL as the current
33 // master mute and volume settings.
34
35 AudioHwDevice::Flags flags = static_cast<AudioHwDevice::Flags>(0);
36 { // scope for auto-lock pattern
37 AutoMutex lock(mHardwareLock);
38
39 if (0 == mAudioHwDevs.size()) {
40 mHardwareStatus = AUDIO_HW_GET_MASTER_VOLUME;
41 if (NULL != dev->get_master_volume) {
42 float mv;
43 if (OK == dev->get_master_volume(dev, &mv)) {
44 mMasterVolume = mv;
45 }
46 }
47
48 mHardwareStatus = AUDIO_HW_GET_MASTER_MUTE;
49 if (NULL != dev->get_master_mute) {
50 bool mm;
51 if (OK == dev->get_master_mute(dev, &mm)) {
52 mMasterMute = mm;
53 }
54 }
55 }
56
57 mHardwareStatus = AUDIO_HW_SET_MASTER_VOLUME;
58 if ((NULL != dev->set_master_volume) &&
59 (OK == dev->set_master_volume(dev, mMasterVolume))) {
60 flags = static_cast<AudioHwDevice::Flags>(flags |
61 AudioHwDevice::AHWD_CAN_SET_MASTER_VOLUME);
62 }
63
64 mHardwareStatus = AUDIO_HW_SET_MASTER_MUTE;
65 if ((NULL != dev->set_master_mute) &&
66 (OK == dev->set_master_mute(dev, mMasterMute))) {
67 flags = static_cast<AudioHwDevice::Flags>(flags |
68 AudioHwDevice::AHWD_CAN_SET_MASTER_MUTE);
69 }
70
71 mHardwareStatus = AUDIO_HW_IDLE;
72 }
73 //【4】添加到全局变量中：将设备添加到mAudioHwDevs键值对中，
74 //key:handle = nextUniqueId(),保证audio_interface具有全局唯一的id;
75 audio_module_handle_t handle = nextUniqueId();
76 mAudioHwDevs.add(handle, new AudioHwDevice(handle, name, dev, flags));
77
78 ALOGI("loadHwModule() Loaded %s audio interface from %s (%s) handle %d",
79 name, dev->common.module->name, dev->common.module->id, handle);
80
81 return handle;
}
2.打开音频设备
1 sp<AudioFlinger::PlaybackThread> AudioFlinger::openOutput_l(audio_module_handle_t module,
2 audio_io_handle_t *output,
3 audio_config_t *config,
4 audio_devices_t devices,
5 const String8& address,
6 audio_output_flags_t flags)
7 {
8 /* 【1】查找相应的audio_interface*/
9 AudioHwDevice *outHwDev = findSuitableHwDev_l(module, devices);
10 if (outHwDev == NULL) {
11 return 0;
12 }
13 /*【2】为设备打开一个输入流 */
14 audio_hw_device_t *hwDevHal = outHwDev->hwDevice();
15 if (*output == AUDIO_IO_HANDLE_NONE) {
16 *output = nextUniqueId();
17 }
18
19 mHardwareStatus = AUDIO_HW_OUTPUT_OPEN;
20
21 audio_stream_out_t *outStream = NULL;
22
23 // FOR TESTING ONLY:
24 // This if statement allows overriding the audio policy settings
25 // and forcing a specific format or channel mask to the HAL/Sink device for testing.
26 if (!(flags & (AUDIO_OUTPUT_FLAG_COMPRESS_OFFLOAD | AUDIO_OUTPUT_FLAG_DIRECT))) {
27 // Check only for Normal Mixing mode
28 if (kEnableExtendedPrecision) {
29 // Specify format (uncomment one below to choose)
30 //config->format = AUDIO_FORMAT_PCM_FLOAT;
31 //config->format = AUDIO_FORMAT_PCM_24_BIT_PACKED;
32 //config->format = AUDIO_FORMAT_PCM_32_BIT;
33 //config->format = AUDIO_FORMAT_PCM_8_24_BIT;
34 // ALOGV("openOutput_l() upgrading format to %#08x", config->format);
35 }
36 if (kEnableExtendedChannels) {
37 // Specify channel mask (uncomment one below to choose)
38 //config->channel_mask = audio_channel_out_mask_from_count(4); // for USB 4ch
39 //config->channel_mask = audio_channel_mask_from_representation_and_bits(
40 // AUDIO_CHANNEL_REPRESENTATION_INDEX, (1 << 4) - 1); // another 4ch example
41 }
42 }
43
44 status_t status = hwDevHal->open_output_stream(hwDevHal,
45 *output,
46 devices,
47 flags,
48 config,
49 &outStream,
50 address.string());
51
52 mHardwareStatus = AUDIO_HW_IDLE;
53 ALOGV("openOutput_l() openOutputStream returned output %p, sampleRate %d, Format %#x, "
54 "channelMask %#x, status %d",
55 outStream,
56 config->sample_rate,
57 config->format,
58 config->channel_mask,
59 status);
60
61 if (status == NO_ERROR && outStream != NULL) {
62 /* 【3】生成AudioStreamOut*/
63 AudioStreamOut *outputStream = new AudioStreamOut(outHwDev, outStream, flags);
64 /*【4】创建PlaybackThreadOut*/
65 PlaybackThread *thread;
66 if (flags & AUDIO_OUTPUT_FLAG_COMPRESS_OFFLOAD) {
67 thread = new OffloadThread(this, outputStream, *output, devices);
68 ALOGV("openOutput_l() created offload output: ID %d thread %p", *output, thread);
69 } else if ((flags & AUDIO_OUTPUT_FLAG_DIRECT)
70 || !isValidPcmSinkFormat(config->format)
71 || !isValidPcmSinkChannelMask(config->channel_mask)) {
72 //***new DirectOutputThread
73 thread = new DirectOutputThread(this, outputStream, *output, devices);
74 ALOGV("openOutput_l() created direct output: ID %d thread %p", *output, thread);
75 } else {
76 //***new MixerThread
77 thread = new MixerThread(this, outputStream, *output, devices);
78 ALOGV("openOutput_l() created mixer output: ID %d thread %p", *output, thread);
79 }
80 /*【5】 添加播放线程*/
81 mPlaybackThreads.add(*output, thread);
82 return thread;
83 }
84
85 return 0;
86 }
所做的工作：
【1】 查找合适的音频接口与设备；
【2】创建音频输出流（open_output_stream 获得一个audio_stream_out_t）
【3】利用AudioStreamOut封转audio_stream_out_t和audio_hw_device_t；
【4】创建播放线程；
【5】如果当前设备是主设备，则还需要进行相应的设置；
3.findSuitableHwDev_l 查找当前系统的设备
1 AudioFlinger::AudioHwDevice* AudioFlinger::findSuitableHwDev_l( 2 audio_module_handle_t module, 3 audio_devices_t devices) 4 { 5 // if module is 0, the request comes from an old policy manager and we should load 6 // well known modules 7 /* 特殊的module值，此时需要加载所有interface*/ 8 if (module == 0) { 9 ALOGW("findSuitableHwDev_l() loading well know audio hw modules"); 10 for (size_t i = 0; i < ARRAY_SIZE(audio_interfaces); i++) { 11 loadHwModule_l(audio_interfaces[i]); 12 } 13 // then try to find a module supporting the requested device. 14 /* 然后再查找符合要求的device*/ 15 for (size_t i = 0; i < mAudioHwDevs.size(); i++) { 16 AudioHwDevice *audioHwDevice = mAudioHwDevs.valueAt(i); 17 audio_hw_device_t *dev = audioHwDevice->hwDevice(); 18 if ((dev->get_supported_devices != NULL) && 19 (dev->get_supported_devices(dev) & devices) == devices) 20 return audioHwDevice; 21 } 22 } else {/* 直接从记录中记录device*/ 23 // check a match for the requested module handle 24 AudioHwDevice *audioHwDevice = mAudioHwDevs.valueFor(module); 25 if (audioHwDevice != NULL) { 26 return audioHwDevice; 27 } 28 } 29 30 return NULL; 31 }
