From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pierre-Louis Bossart Subject: Re: [very-RFC 0/8] TSN driver for the kernel Date: Mon, 20 Jun 2016 13:08:27 +0200 Message-ID: <9a5abd48-4da3-945d-53c9-b6d37010ab0d@linux.intel.com> References: <1465686096-22156-1-git-send-email-henrik@austad.us> <20160613114713.GA9544@localhost.localdomain> <20160613195136.GC2441@netboy> <20160614121844.54a125a5@lxorguk.ukuu.org.uk> <5760C84C.40408@sakamocchi.jp> <20160615080602.GA13555@localhost.localdomain> <5764DA85.3050801@sakamocchi.jp> <20160618224549.GF32724@icarus.home.austad.us> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by alsa0.perex.cz (Postfix) with ESMTP id 3EF6F26507F for ; Mon, 20 Jun 2016 13:08:16 +0200 (CEST) In-Reply-To: <20160618224549.GF32724@icarus.home.austad.us> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: alsa-devel-bounces@alsa-project.org To: Henrik Austad , Takashi Sakamoto Cc: alsa-devel@alsa-project.org, netdev@vger.kernel.org, Richard Cochran , linux-kernel@vger.kernel.org, Arnd Bergmann , linux-media@vger.kernel.org List-Id: alsa-devel@alsa-project.org > Presentation time is either set by > a) Local sound card performing capture (in which case it will be 'capture > time') > b) Local media application sending a stream accross the network > (time when the sample should be played out remotely) > c) Remote media application streaming data *to* host, in which case it will > be local presentation time on local soundcard > >> This value is dominant to the number of events included in an IEC 61883-1 >> packet. If this TSN subsystem decides it, most of these items don't need >> to be in ALSA. > > Not sure if I understand this correctly. > > TSN should have a reference to the timing-domain of each *local* > sound-device (for local capture or playback) as well as the shared > time-reference provided by gPTP. > > Unless an End-station acts as GrandMaster for the gPTP-domain, time set > forth by gPTP is inmutable and cannot be adjusted. It follows that the > sample-frequency of the local audio-devices must be adjusted, or the > audio-streams to/from said devices must be resampled. The ALSA API provides support for 'audio' timestamps (playback/capture rate defined by audio subsystem) and 'system' timestamps (typically linked to TSC/ART) with one option to take synchronized timestamps should the hardware support them. The intent was that the 'audio' timestamps are translated to a shared time reference managed in userspace by gPTP, which in turn would define if (adaptive) audio sample rate conversion is needed. There is no support at the moment for a 'play_at' function in ALSA, only means to control a feedback loop.