On Tue, Sep 18, 2007 at 10:07:05AM +0200, Ludovico Verducci wrote: > 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: > >>> 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. Ah, I misunderstood what you meant. > 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. I'm aware that some Windows users are using several Delta 1010s without external sync, but I'm not sure how it is done (or how good it sounds). AFAIK it would require a VCXO so that the frequency of the card's clock could be varied by enough to keep it in sync (ie. making the clock oscillator part of a phase locked loop). Looking at the PCI card on the 1010, I can only see standard fixed-frequency crystals. The only PLLs appear to be the internal PLL in the S/PDIF receiver and the 4046 PLL chip for the word clock input signal. John _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
