我们知道，最终控制是从AudioFlinger调用了HAL层的，那么这文就从AudioFlinger开始分析
AudioFlinger初始化
frameworks/av/media/mediaserver/main_mediaserver.cpp
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| int main(int argc __unused, char** argv)
{
AudioFlinger::instantiate();
}
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frameworks/av/services/audioflinger/AudioFlinger.cpp
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| class AudioFlinger :
public BinderService<AudioFlinger>,
public BnAudioFlinger
{
}
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frameworks/native/include/binder/BinderService.h
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| template<typename SERVICE>
class BinderService
{
public:
static status_t publish(bool allowIsolated = false) {
sp<IServiceManager> sm(defaultServiceManager());
return sm->addService(
String16(SERVICE::getServiceName()),
new SERVICE(), allowIsolated);
}
static void instantiate() { publish(); }
};
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这里可以看到，最终调用publish()就是一套进程间Service，初始化是通过强指针引用(constsp&)，将AudioFlinger参考初始化为实体，供外部调用。
加载
frameworks/av/services/audioflinger/AudioFlinger.cpp
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| static const char * const audio_interfaces[] = {
AUDIO_HARDWARE_MODULE_ID_PRIMARY,
AUDIO_HARDWARE_MODULE_ID_A2DP,
AUDIO_HARDWARE_MODULE_ID_USB,
};
AudioFlinger::AudioHwDevice* AudioFlinger::findSuitableHwDev_l(
audio_module_handle_t module,
audio_devices_t devices)
{
for (size_t i = 0; i < ARRAY_SIZE(audio_interfaces); i++) {
loadHwModule_l(audio_interfaces[i]);
}
audio_module_handle_t AudioFlinger::loadHwModule_l(const char *name)
{
int rc = load_audio_interface(name, &dev);
}
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| static int load_audio_interface(const char *if_name, audio_hw_device_t **dev)
{
rc = hw_get_module_by_class(AUDIO_HARDWARE_MODULE_ID, if_name, &mod);
ALOGE_IF(rc, "%s couldn't load audio hw module %s.%s (%s)", __func__,
AUDIO_HARDWARE_MODULE_ID, if_name, strerror(-rc));
rc = audio_hw_device_open(mod, dev);
}
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hardware/libhardware/hardware.c
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| int hw_get_module_by_class(const char *class_id, const char *inst,
const struct hw_module_t **module)
{
if (inst)
snprintf(name, PATH_MAX, "%s.%s", class_id, inst);
else
strlcpy(name, class_id, PATH_MAX);
snprintf(prop_name, sizeof(prop_name), "ro.hardware.%s", name);
if (property_get(prop_name, prop, NULL) > 0) {
if (hw_module_exists(path, sizeof(path), name, prop) == 0) {
goto found;
}
}
for (i=0 ; i<HAL_VARIANT_KEYS_COUNT; i++) {
if (property_get(variant_keys[i], prop, NULL) == 0) {
continue;
}
if (hw_module_exists(path, sizeof(path), name, prop) == 0) {
goto found;
}
}
if (hw_module_exists(path, sizeof(path), name, "default") == 0) {
goto found;
}
}
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frameworks/av/services/audioflinger/AudioFlinger.cpp
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| audio_module_handle_t AudioFlinger::loadHwModule_l(const char *name)
{
audio_hw_device_t *dev;
int rc = load_audio_interface(name, &dev);
rc = dev->init_check(dev);
audio_module_handle_t handle = nextUniqueId();
mAudioHwDevs.add(handle, new AudioHwDevice(handle, name, dev, flags));
}
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这里是从findSuitableHwDev_l开始，调用位置在上一篇有入口，这里就不多提了
最终打开的路经为：/system/lib/hw/audio.primary.rk30board.so参考，最终接入口传在了audio_hw_device_t指针结构体中
注：audio_hw_device_t结构体定义位置：/libhardware/include/hardware/audio.h
所以，此时，hal的audio已经化身了AudioHwDevice类，audio_hw_device_t变成了类成员mHwDevice(hwDevice)
frameworks/av/services/audioflinger/AudioFlinger.h
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| class AudioHwDevice {
public:
enum Flags {
AHWD_CAN_SET_MASTER_VOLUME = 0x1,
AHWD_CAN_SET_MASTER_MUTE = 0x2,
};
AudioHwDevice(audio_module_handle_t handle,
const char *moduleName,
audio_hw_device_t *hwDevice,
Flags flags)
: mHandle(handle), mModuleName(strdup(moduleName))
, mHwDevice(hwDevice)
, mFlags(flags) { }
audio_hw_device_t *hwDevice() const { return mHwDevice; }
};
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从构造函数来看，接下来就是搜hwDevice()方法，在AudioFlinger.cpp有好多地方调用，它就是hal的audio
