John Rigg ha scritto: > On Mon, Sep 17, 2007 at 08:44:03PM +0100, John Rigg wrote: > >> On Mon, Sep 17, 2007 at 12:22:19PM +0200, Ludovico Verducci wrote: >> >>> Hello all! >>> >>> I'm developing a complex multichannel audio distribution system where >>> multiple linux boxes will stream audio data over ethernet and then >>> should play audio at sample level resolution synchronization. The boxes >>> clocks are synchronized over ethernet using PTP. >>> I need to keep in synch the audio board's clocks and I can't use an >>> external wordclock nor s/pdif. >>> >> Won't this cause serious clock jitter problems? I don't see how the >> PCI bus can deliver precise enough timing, considering how much other >> data it has to handle. >> I didn't mean to directly drive the audio board's clock over the PCI bus. I think this is simply not feasible. But I think that using control signals periodically exchanged over PCI between the audio board and the kernel could be possible (if the hardware could support a similar feature, of course) to skew the board's clock to keep it in synch with a software reference. As far as I know the delta family boards drivers support the synchronization of up to 4 audio boards over PCI: at the moment I'm reverse engineering the hardware trying to understand how this can be accomplished. > > And I can't see any way that the clocks can be synced to sample > accuracy over ethernet. That's what external word clocks are for. > Even with a word clock I suspect that the latency of the > ethernet connection would be too high to allow sample accurate sync > of the audio. > > John > The machines real time clocks are synched over ethernet using Precision Time Protocol. This protocol can achieve below 1 microsecond synchronization accuracy. This should be fine to sample level synch at 48 KHz. Regards, Ludovico _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
