Re: ALSA snd_xferi_t buffer arrangment

[James Courtier-Dutton <James@superbug.co.uk>]

Assaf Hoffman wrote:
> Thank you for your reply.
> Please let me clarify. What you say is that my device can deliver a raw
> ICE958 data from the capture channel to the DMA buffer and the ALSA
> stack will know how to deal with it? No need for the device to strip
> down the payload and only then transfer it to the DMA buffer?
> In case the sound card can strip down the IEC958 frames into raw sound
> data + ch status + user data, how would the ALSA stack expect the data?
> Is there an API for that?
> Thanks again.
> 

If you don't strip the IEC958 frames, tell ALSA the format is:
SNDRV_PCM_FMTBIT_IEC958_SUBFRAME_LE
SNDRV_PCM_FMTBIT_IEC958_SUBFRAME_BE
If you do strip the IEC958 frames, tell ALSA the format is:
SNDRV_PCM_FMTBIT_S24_LE or
SNDRV_PCM_FMTBIT_S16_LE

Or whatever format your hardware decides to send.

The API for this is contained in the following structure in the sound
driver:
This example is from the snd-emu10k1 driver.

static struct snd_pcm_hardware snd_emu10k1_capture =
{
        .info =                 (SNDRV_PCM_INFO_MMAP |
SNDRV_PCM_INFO_INTERLEAVED |
                                 SNDRV_PCM_INFO_BLOCK_TRANSFER |
                                 SNDRV_PCM_INFO_RESUME |
                                 SNDRV_PCM_INFO_MMAP_VALID),
        .formats =              SNDRV_PCM_FMTBIT_S16_LE,
        .rates =                SNDRV_PCM_RATE_8000_48000,
        .rate_min =             8000,
        .rate_max =             48000,
        .channels_min =         1,
        .channels_max =         2,
        .buffer_bytes_max =     (64*1024),
        .period_bytes_min =     384,
        .period_bytes_max =     (64*1024),
        .periods_min =          2,
        .periods_max =          2,
        .fifo_size =            0,
};


As you can see, it tells use that this device can do only
SNDRV_PCM_FMTBIT_S16_LE format.

James


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