PCM DUMP

最新推荐文章于 2024-04-03 11:04:47 发布

dhf898989

最新推荐文章于 2024-04-03 11:04:47 发布

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本文链接：https://blog.youkuaiyun.com/dhf898989/article/details/47336163

本文详细介绍了如何在Linux内核中实现PCM DUMP，利用ALSA Capture接口和USBAudio设备创建音频循环。通过在sound/usb/pcm.c文件中添加和替换操作集，实现AudioCapture节点，并最终添加新的AudioCapture节点以完成Kernel级别的音频处理。

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【ALSA】【USBAudio】【PCMDUMP】

基本原理

通过ALSA Capture 提供的接口，在kernel实现Audioloop.

Kernel实现

1. 实现AudioCapture节点操作集

在sound/usb/pcm.c加入如下代码：

struct usb_dummy_capture{
        struct snd_pcm_substream *pcm_substream;
        snd_pcm_format_t pcm_format;    /* current audio format (for hw_params callback) */
        unsigned int channels;          /* current number of channels (for hw_params callback) */
        unsigned int cur_rate;          /* current rate (for hw_params callback) */
        unsigned int period_bytes;      /* current period bytes (for hw_params callback) */
        unsigned int running: 1;        /* running status */
        unsigned int hwptr_done;        /* processed byte position in the buffer */
        unsigned int transfer_done;             /* processed frames since last period update */

};

static struct usb_dummy_capture g_dummy_capture;

static struct snd_pcm_hardware snd_usb_dummy_hardware =
{
        .info =                 SNDRV_PCM_INFO_MMAP |
                                SNDRV_PCM_INFO_MMAP_VALID |
                                SNDRV_PCM_INFO_BATCH |
                                SNDRV_PCM_INFO_INTERLEAVED |
                                SNDRV_PCM_INFO_BLOCK_TRANSFER |
                                SNDRV_PCM_INFO_PAUSE,
        .formats = SNDRV_PCM_FMTBIT_S16_LE,
        .rates    = SNDRV_PCM_RATE_48000,
        .rate_min = 48000,
        .rate_max = 48000,
        .channels_min = 2,
        .channels_max = 2,
        .buffer_bytes_max =     1024 * 1024,
        .period_bytes_min =     64,
        .period_bytes_max =     512 * 1024,
        .periods_min =          2,
        .periods_max =          1024,
};


static int snd_usb_dummy_open(struct snd_pcm_substream *substream)
{
    g_dummy_capture.pcm_substream = substream;
        struct snd_pcm_runtime *runtime = substream->runtime;

        runtime->hw