浅析alsa声卡驱动snd_pcm_start函数－将音频数据真实的发送到外部音频接口硬件

来源：互联网发布：时时彩组选计划软件编辑：程序博客网时间：2024/04/30 23:06

转载自链接：浅析alsa声卡驱动snd_pcm_start函数－将音频数据真实的发送到外部音频接口硬件-gliethttp-ChinaUnix博客 http://blog.chinaunix.net/uid-20564848-id-74236.html

将音频数据真实的发送到外部音频接口硬件
/**
* snd_pcm_start - start all linked streams
* @substream: the PCM substream instance
*/
int snd_pcm_start(struct snd_pcm_substream *substream)
{
    // 启动发送,将streams中的所有音频数据递交到硬件[luther.gliethttp]
    // 执行snd_pcm_action_start
    // ==> snd_pcm_do_start
    // ==> substream->ops->trigger(substream, SNDRV_PCM_TRIGGER_START);
    // ==> 即调用soc_pcm_ops.soc_pcm_trigger
    // ==> platform->pcm_ops->trigger
    // ==> 最后调用s3c24xx_pcm_trigger启动s3c24xx处理器的DMA通道发送音频数据到外围接口硬件[luther.gliethttp]
    // 这里的platform就是s3c24xx_soc_platform
    // struct snd_soc_platform s3c24xx_soc_platform = {
    //   .name       = "s3c24xx-audio",
    //   .pcm_ops    = &s3c24xx_pcm_ops,
    //   .pcm_new   = s3c24xx_pcm_new,
    //   .pcm_free   = s3c24xx_pcm_free_dma_buffers,
    //};
    // static struct snd_pcm_ops s3c24xx_pcm_ops = {
    //   .open       = s3c24xx_pcm_open,
    //   .close       = s3c24xx_pcm_close,
    //   .ioctl       = snd_pcm_lib_ioctl,
    //   .hw_params   = s3c24xx_pcm_hw_params,
    //   .hw_free   = s3c24xx_pcm_hw_free,
    //   .prepare   = s3c24xx_pcm_prepare,
    //   .trigger   = s3c24xx_pcm_trigger,
    //   .pointer   = s3c24xx_pcm_pointer,
    //   .mmap       = s3c24xx_pcm_mmap,
    //};
   return snd_pcm_action(&snd_pcm_action_start, substream,
                  SNDRV_PCM_STATE_RUNNING);
}

0 0