[alsa-devel] PulseAudio and SNDRV_PCM_INFO_BATCH

[Raymond Yau]

> >> Are all soc audio driver use cyclic dma ?
> >
> > I'm not sure I understand the question. All audio drivers use some
> > kind of cyclic DMA.
>
> The ALSA API requires the driver to provide a cyclic sample buffer (or
> something that behaves like one).
>
> However, not all hardware works this way.  USB and FireWire require the
> driver to continually queue new packets, whose size and timing are
> determined by the bus clock and are not directly related to the ALSA
> ring buffer.  These drivers use double buffering; the actual DMA happens
> from those packets, not from the ring buffer.
>

If those queued packets/urb cannot be rewind, snd_pcm_rewindable should
return zero for those driver