linux-kernel - Re: [alsa-devel] [very-RFC 0/8] TSN driver for the kernel

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Date:	Mon, 20 Jun 2016 14:18:38 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Cc:	Henrik Austad <henrik@...tad.us>,
	Takashi Sakamoto <o-takashi@...amocchi.jp>,
	alsa-devel@...a-project.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...aro.org>,
	linux-media@...r.kernel.org
Subject: Re: [alsa-devel] [very-RFC 0/8] TSN driver for the kernel

On Mon, Jun 20, 2016 at 01:08:27PM +0200, Pierre-Louis Bossart wrote:
> 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.

Thanks for the info.  I just skimmed Documentation/sound/alsa/timestamping.txt.

That is fairly new, only since v4.1.  Are then any apps in the wild
that I can look at?  AFAICT, OpenAVB, gstreamer, etc, don't use the
new API.

> 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.

Documentation/sound/alsa/timestamping.txt says:

  If supported in hardware, the absolute link time could also be used
  to define a precise start time (patches WIP)

Two questions:

1. Where are the patches?  (If some are coming, I would appreciate
   being on CC!)

2. Can you mention specific HW that would support this?


Thanks,
Richard