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From: Clemens Ladisch <clemens@ladisch.de>
To: Alan Horstmann <gineera@aspect135.co.uk>
Cc: Takashi Iwai <tiwai@suse.de>, alsa-devel@alsa-project.org
Subject: Re: _mmap_playback_avail() short
Date: Mon, 28 Nov 2011 22:12:53 +0100	[thread overview]
Message-ID: <4ED3F955.4090904@ladisch.de> (raw)
In-Reply-To: <201111251510.27592.gineera@aspect135.co.uk>

Alan Horstmann wrote:
>> It seems that at a period boundary event snd_pcm_mmap_playback_avail() may
>> not return a full period size, but is a few bytes short.  If avail_min is
>> set to one whole period (which Portaudio at present does),
>> snd_pcm_direct_poll_revents() zeroes the revent due to the check of
>> snd_pcm_mmap_playback_avail() against avail_min.  POLLOUT is therefore not
>> indicated, and the app does not write any data, causing an Xrun.

This sounds like a bug in the rate plugin.  snd_pcm_rate_sync_hwptr()
tries to properly align pointer values at period boundaries, but its
algorithm doesn't work when a period does not start at the buffer start
(i.e., when the number of periods is not an integer), and this
restriction is not actually enforced by snd_pcm_rate_hw_refine_cchange().

As a workaround, try snd_pcm_hw_params_set_periods_integer().


Regards,
Clemens

  parent reply	other threads:[~2011-11-28 21:13 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-10-31 17:38 Default device XRUNs with perriods=2 Alan Horstmann
2011-11-03 10:03 ` _mmap_playback_avail() short (was: Default device XRUNs with perriods=2) Alan Horstmann
2011-11-25 15:10   ` Alan Horstmann
2011-11-27  1:40     ` Raymond Yau
2011-11-28 11:03       ` Alan Horstmann
2011-11-28 21:12     ` Clemens Ladisch [this message]
2011-11-29 14:07       ` _mmap_playback_avail() short Alan Horstmann
2011-11-29 15:21         ` Clemens Ladisch
2011-11-29 22:07           ` Alan Horstmann

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