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

Richard Cochran
2016-06-13T19:51:41Z

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