On Fri, 4 Sep 2009, Lennart Poettering wrote: > Heya! > > I am looking for a way to find out whether the clocks of two > snd_pcm_t's are perfectly in sync and don't deviate (or only deviate > by a constant phase). > > i.e. for real duplex devices that use the same crystal for input and > output this should tell me "Yes" for the playback snd_pcm_t tested > against the recording snd_pcm_t; and for all other, unrelated audio > devices it should return "No". > > I found snd_pcm_info_get_sync() in the docs, but its documentation is > a bit terse, so I am wondering if this might be what I want. Is it? > > Does this (untested) code snippet do what I hope it does? Hi, Nope. The snd_pcm_info_get_sync() function identifies streams with "sample sync and sample synchronized start". All standard soundcards have only one clock source, so if snd_pcm_info_get_card() number matches, the streams will most probably run in sync. I cannot recall from my mind, if any card has two clock sources - maybe only old Gravis UltraSound hardware with GF1 and CS4231 chips, but it's history. Also, professional hardware can run with word clock sync (wire connection carrying sample clock) or S/PDIF clock sync. But it's matter of user configuration. I would suggest to match card number as default for used streams and add an user option to modify the stream word clock configuration for your app. 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
