[alsa-devel] What does snd_pcm_delay() actually return?
perex at perex.cz
Fri Jun 13 10:14:33 CEST 2008
On Fri, 13 Jun 2008, Takashi Iwai wrote:
> - Add some new API functions,
I would prefer to extend the current API than to change meaning of hw_ptr
to handle extra latencies.
> * To give the accuracy of the position inquiry (optional)
> This requires some new kernel <-> user-space stuff.
> * To query the known latency
> Ditto, or we may reuse snd_pcm_hw_params_fifo_size()?
Yes, fifo_size was designed to announce possible extra latency to
> * To query the position being played (optionally)
> This can be simply hwptr + latency.
> - Don't change snd_pcm_delay(). Keep as is now.
> About the period model -- it's a bit more tough problem.
> I once already made a patch to allow user-apps to use a system timer
> for more flexible period settings. But, it was for very old version
> of ALSA. Better to write from the scratch again...
I think that the current PCM API concept is tightly period based. You
cannot change it easily. It would be probably better to move to
"byte-stream" in next revision of PCM API.
Jaroslav Kysela <perex at perex.cz>
Linux Kernel Sound Maintainer
ALSA Project, Red Hat, Inc.
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