Audio outStream and Volume Gain

最新推荐文章于 2025-03-29 11:17:53 发布

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本文深入解析Android音频HAL层，涵盖HAL、Kernel与Codec寄存器关键概念。介绍HAL硬件层结构，包括audio_module、audio_hw_device及hw_module_methods_t，探讨RK3399项目中的音频实现，并简述Kernel层面的ALSA驱动。

Audio Stream and Volume Gain

Audio Stream and Volume Gain

音频outstream简介

audio框架在Android系统中占据很大用户市场，音频的复杂，Android框架一直在调整中。
看一张高通的音频各个场景的路径：
这里写图片描述

这张图片来着高通，各个芯片方案路线基本一致。对于HAL上层已经在前面两篇文章进行了分析，这篇重要分析HAL、 Kernel、CODEC寄存器。
用项目RK3399 来理解。

HAL

HAL hardware Layer是与kernel最接近的一层，通过IOCTL与kernel进行通信。将对应的操作封装到厂商动态链接库。
简述如何实现HAL层模块。
先简单介绍重要的三个结构体：
hw_module_t: 描述硬件模块基类
hw_device_t: 描述硬件设备基类
hw_module_methods_t: 打开硬件模块种包含的硬件设备，获得指向硬件设备结构体的指针。
这里写图片描述

Audio HAL实现步骤

1 struct audio_module

/**
 * Every hardware module must have a data structure named HAL_MODULE_INFO_SYM
 * and the fields of this data structure must begin with hw_module_t
 * followed by module specific information.
 */
struct audio_module {
    struct hw_module_t common;
};

定义 audio_module 的 HAL_MODULE_INFO_SYM 变量

struct audio_module HAL_MODULE_INFO_SYM = {
    .common = {
        .tag = HARDWARE_MODULE_TAG,
        .module_api_version = AUDIO_MODULE_API_VERSION_0_1,
        .hal_api_version = HARDWARE_HAL_API_VERSION,
        .id = AUDIO_HARDWARE_MODULE_ID,
        .name = "QCOM Audio HAL",
        .author = "The Linux Foundation",
        .methods = &hal_module_methods,
    },
};

2 struct audio_hw_device

struct audio_hw_device {
    /**
     * Common methods of the audio device.  This *must* be the first member of audio_hw_device
     * as users of this structure will cast a hw_device_t to audio_hw_device pointer in contexts
     * where it's known the hw_device_t references an audio_hw_device.
     */
    struct hw_device_t common;



    /** set the audio volume of a voice call. Range is between 0.0 and 1.0 */
    int (*set_voice_volume)(struct audio_hw_device *dev, float volume);


    int (*set_master_volume)(struct audio_hw_device *dev, float volume);


    int (*get_master_volume)(struct audio_hw_device *dev, float *volume);


    int (*set_mode)(struct audio_hw_device *dev, audio_mode_t mode);

    /* mic mute */
    int (*set_mic_mute)(struct audio_hw_device *dev, bool state);
    int (*get_mic_mute)(const struct audio_hw_device *dev, bool *state);

    /* set/get global audio parameters */
    int (*set_parameters)(struct audio_hw_device *dev, const char *kv_pairs);


    char * (*get_parameters)(const struct audio_hw_device *dev,
                             const char *keys);


    size_t (*get_input_buffer_size)(const struct audio_hw_device *dev,
                                    const struct audio_config *config);



    int (*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);

    void (*close_output_stream)(struct audio_hw_device *dev,
                                struct audio_stream_out* stream_out);

    /** This method creates and opens the audio hardware input stream */
    int (*open_input_stream)(struct audio_hw_device *dev,
                             audio_io_handle_t handle,
                             audio_devices_t devices,
                             struct audio_config *config,
                             struct audio_stream_in **stream_in,
                             audio_input_flags_t flags,
                             const char *address,
                             audio_source_t source);

    void (*close_input_stream)(struct audio_hw_device *dev,
                               struct audio_stream_in *stream_in);
    int (*set_master_mute)(struct audio_hw_device *dev, bool mute);
    int (*get_master_mute)(struct audio_hw_device *dev, bool *mute);
    ...
};

audio_hw_device 的定义中，第一个结构体成员就是 struct hw_device_t 类型的，而其他的结构体成员都是函数指针， open_output_stream 函数就是用来打开播放音频的扬声器设备，open_input_stream 函数则是用来打开录音用的麦克风设备。

3 struct hw_module_methods_t 函数列表

hardware\qcom\audio\hal\audio_hw.c

static struct hw_module_methods_t hal_module_methods = {
    .open = adev_open,
};

hardware\qcom\audio\hal\audio_hw.c

static int adev_open(const hw_module_t *module, const char *name,
                     hw_device_t **device)
{
    int i, ret;
    /hw_device 初始化
    adev->device.common.tag = HARDWARE_DEVICE_TAG;
    adev->device.common.version = AUDIO_DEVICE_API_VERSION_2_0;
    adev->device.common.module = (struct hw_module_t *)module;
    adev->device.common.close = adev_close;
    /函数列表...
    adev->device.init_check = adev_init_check;
    adev->device.set_voice_volume = adev_set_voice_volume;
    adev->device.set_master_volume = adev_set_master_volume;
    adev->device.get_master_volume = adev_get_master_volume;
    adev->device.set_master_mute = adev_set_master_mute;
    adev->device.get_master_mute = adev_get_master_mute;
    adev->device.set_mode = adev_set_mode;
    adev->device.set_mic_mute = adev_set_mic_mute;
    adev->device.get_mic_mute = adev_get_mic_mute;
    adev->device.set_parameters = adev_set_parameters;
    adev->device.get_parameters = adev_get_parameters;
    adev->device.get_input_buffer_size = adev_get_input_buffer_size;
    adev->device.open_output_stream = adev_open_output_stream;
    adev->device.close_output_stream = adev_close_output_stream;
    adev->device.open_input_stream = adev_open_input_stream;
    adev->device.close_input_stream = adev_close_input_stream;
    adev->device.dump = adev_dump;
    ...
    return 0