On Mon, 20 Apr 2009, Nicola Mfb wrote: > Hi! > I'm sorry if this is an old issue but I did not found help in > archives/alsaweb/google and I'm new to alsa, so this report is what I > guessed reading sources and compiling test apps for about 2 days, and > the following assumptions may be completely wrong. > > Asterisk has an alsa channel that works fine when using plughw:0,0 > both for read and for writing, but if use plug:dmix/plug:dsnoop or > default with a dmix/dsnoop wrapper in /etc/asound.conf it does not > emit any sound. It uses select on poll fd descriptor to know if the > pcm is ready to be sent output samples. > The select will never return as it seems the dmix plugin is not able > to signal when is ready. > I noted that using snd_pcm_wait works well but cannot be used in > asterisk as it needs to select on two fd. > I guess that snd_pcm_wait with dmix check the shared memory and not > the fd descriptor. > So should poll/select be avoided completely in applications (as they > does not know if the default pcm is a dmix) and asterisk alsa channel > be rewritten or is there a workaround? Asterisk does not use snd_pcm_poll_descriptors_revents to translate events returned from poll to correct poll event. Also, only file descriptor number from snd_pcm_poll_descriptors() - asterisk should handle correctly returned poll events as well. See chan_alsa.c - readdev / writedev variables and sound_thread(). Jaroslav ----- Jaroslav Kysela <perex@xxxxxxxx> Linux Kernel Sound Maintainer ALSA Project, Red Hat, Inc. _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
