On Fri, 04.09.09 07:52, pl bossart (bossart.nospam@xxxxxxxxx) wrote: > > > 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). > > short answer:no > You would need hardware that would count the bit clock transitions and > provide the delta. Few devices provide this in the consumer space, and > when they do they actually perform an asynchronous sample-rate > conversion on the fly (cf. Freescale DSP563xx). Analog Devices also > provides dedicated sample-rate converters that perform this comparison > and resampling; they are typically used when multiple masters are > present. > All this nice hardware wouldn't work anyway for USB where audio is > transmitted in packets every ms; it's hard to guess what the real > audio speed is. But that should already be good enough for my purposes. I mostly care that over a longer period of time the deviation between input and output (or two outputs) is bounded. That means, if there is a fixed time deviation between recording and playback and I know only that it is fixed but don't know exactly what it is I am already a happier man. > That's the reason why I introduced the resampling enable/disable in > the PA module-loopback code, only the user/system designer will know > if you have one master or more, and whether you should enable > variable-rate interpolation. but why shouldn't this information be queriable from the drivers? Drivers do know a lot about the hardware they drive, so they should now about clocks, too. Lennart -- Lennart Poettering Red Hat, Inc. lennart [at] poettering [dot] net http://0pointer.net/lennart/ GnuPG 0x1A015CC4 _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
