From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ludovico Verducci Subject: Re: Enabling in-kernel synch for M-Audio boards Date: Tue, 18 Sep 2007 10:07:05 +0200 Message-ID: <46EF8729.3080901@alice.it> References: <46EE555B.9000700@alice.it> <20070917194403.GA3655@localhost> <20070918065723.GA2512@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mercurio1.dnshostplan.com (dns22.dnshostplan.com [151.1.210.227]) by alsa0.perex.cz (Postfix) with ESMTP id 69EAA24471 for ; Tue, 18 Sep 2007 10:07:09 +0200 (CEST) Received: from host9-74-static.89-82-b.business.telecomitalia.it ([82.89.74.9] helo=[10.10.1.203]) by mercurio1.dnshostplan.com with esmtpa (Exim 4.68) (envelope-from ) id 1IXY6p-0000KL-7R for alsa-devel@alsa-project.org; Tue, 18 Sep 2007 10:07:03 +0200 In-Reply-To: <20070918065723.GA2512@localhost> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: alsa-devel-bounces@alsa-project.org Errors-To: alsa-devel-bounces@alsa-project.org To: alsa-devel@alsa-project.org List-Id: alsa-devel@alsa-project.org 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