[alsa-devel] What does snd_pcm_delay() actually return?

Lennart Poettering mznyfn at 0pointer.de
Fri Jun 13 16:29:23 CEST 2008

On Fri, 13.06.08 15:55, Jaroslav Kysela (perex at perex.cz) wrote:

> On Fri, 13 Jun 2008, Lennart Poettering wrote:
> > c) snd_pcm_hw_params_get_buffer_size() - snd_pcm_update_avail()
> >    returns the fill level, but only works on mmap.
> snd_pcm_update_avail() works (or should work) also for standard r/w
> ops.

Ok, so it's just the documentation that needs fixing? Quoting: "Using
of this function is useless for the standard read/write
operations. Use it only for mmap access."

> > d) The snd_pcm_hw_params_get_fifo_size() was supposed to return the
> >    'difference' between a) and c), but was never actually used
> >    for that.
> Nope. It's maximum latency added by an extra fifo/queue (it does not 
> depend if it's hw or sw fifo). For variable fifo size, we need to extend 
> API.

Ok, so it's an upper ceiling for the difference between a) and c), right?


Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net         ICQ# 11060553
http://0pointer.net/lennart/           GnuPG 0x1A015CC4

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