From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Cochran Subject: Re: [very-RFC 0/8] TSN driver for the kernel Date: Mon, 13 Jun 2016 21:51:36 +0200 Message-ID: <20160613195136.GC2441@netboy> References: <1465686096-22156-1-git-send-email-henrik@austad.us> <20160613114713.GA9544@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, alsa-devel@vger.kernel.org, netdev@vger.kernel.org, henrk@austad.us, Arnd Bergmann To: Henrik Austad Return-path: Content-Disposition: inline In-Reply-To: <20160613114713.GA9544@localhost.localdomain> Sender: linux-media-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Mon, Jun 13, 2016 at 01:47:13PM +0200, Richard Cochran wrote: > 3. ALSA support for tunable AD/DA clocks. The rate of the Listener's > DA clock must match that of the Talker and the other Listeners. > Either you adjust it in HW using a VCO or similar, or you do > adaptive sample rate conversion in the application. (And that is > another reason for *not* having a shared kernel buffer.) For the > Talker, either you adjust the AD clock to match the PTP time, or > you measure the frequency offset. Actually, we already have support for tunable clock-like HW elements, namely the dynamic posix clock API. It is trivial to write a driver for VCO or the like. I am just not too familiar with the latest high end audio devices. I have seen audio PLL/multiplier chips that will take, for example, a 10 kHz input and produce your 48 kHz media clock. With the right HW design, you can tell your PTP Hardware Clock to produce a 10000 PPS, and you will have a synchronized AVB endpoint. The software is all there already. Somebody should tell the ALSA guys about it. I don't know if ALSA has anything for sample rate conversion or not, but haven't seen anything that addresses distributed synchronized audio applications. Thanks, Richard