Android音频驱动-ASOC之PCM HW Params

最新推荐文章于 2025-06-20 21:16:13 发布

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最新推荐文章于 2025-06-20 21:16:13 发布 · 3.2k 阅读

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CC 4.0 BY-SA版权

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#android

本文详细探讨了Android音频驱动中ASOC(Advanced Linux Sound Architecture)子系统PCM硬件参数设置的过程，从ALSA的HW_param流程入手，逐层剖析了从soc_pcm_hw_params到平台driver的hw_params操作，包括codec_dai和cpu_dai的驱动实现细节，为理解Android音频驱动的工作原理提供深入见解。

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ALSA的HW_param流程

soc_pcm_hw_params => rtd->dai_link->ops->hw_params => codec_dai->driver->ops->hw_params =>
cpu_dai->driver->ops->hw_params => platform->driver->ops->hw_params

struct pcm *pcm_open(unsigned int card, unsigned int device,
                     unsigned int flags, struct pcm_config *config)
{
    struct pcm *pcm;
    struct snd_pcm_info info;
    struct snd_pcm_hw_params params;
    struct snd_pcm_sw_params sparams;
    char fn[256];
    int rc;

    pcm = calloc(1, sizeof(struct pcm));
    if (!pcm || !config)
        return &bad_pcm; /* TODO: could support default config here */

    pcm->config = *config;

    snprintf(fn, sizeof(fn), "/dev/snd/pcmC%uD%u%c", card, device,
             flags & PCM_IN ? 'c' : 'p');

    pcm->flags = flags;
    pcm->fd = open(fn, O_RDWR);

    if (ioctl(pcm->fd, SNDRV_PCM_IOCTL_INFO, &info)) {
        oops(pcm, errno, "cannot get info");
        goto fail_close;
    }

    param_init(&params);
    param_set_mask(&params, SNDRV_PCM_HW_PARAM_FORMAT,
                   pcm_format_to_alsa(config->format));
    param_set_mask(&params, SNDRV_PCM_HW_PARAM_SUBFORMAT,
                   SNDRV_PCM_SUBFORMAT_STD);
    param_set_min(&params, SNDRV_PCM_HW_PARAM_PERIOD_SIZE, config->period_size);
    param_set_int(&params, SNDRV_PCM_HW_PARAM_SAMPLE_BITS,
                  pcm_format_to_bits(config->format));
    param_set_int(&params, SNDRV_PCM_HW_PARAM_FRAME_BITS,
                  pcm_format_to_bits(config->format) * config->channels);
    param_set_int(&params, SNDRV_PCM_HW_PARAM_CHANNELS,
                  config->channels);
    param_set_int(&params, SNDRV_PCM_HW_PARAM_PERIODS, config->period_count);
    param_set_int(&params, SNDRV_PCM_HW_PARAM_RATE, config->rate);

    param_set_mask(&params, SNDRV_PCM_HW_PARAM_ACCESS,
                       SNDRV_PCM_ACCESS_RW_INTERLEAVED);

    if (ioctl(pcm->fd, SNDRV_PCM_IOCTL_HW_PARAMS, &params)) {
        oops(pcm, errno, "cannot set hw params");
        goto fail_close;
    }

    /* get our refined hw_params */
    config->period_size = param_get_int(&params, SNDRV_PCM_HW_PARAM_PERIOD_SIZE);
    config->period_count = param_get_int(&params, SNDRV_PCM_HW_PARAM_PERIODS);
    pcm->buffer_size = config->period_count * config->