Re: [Jack-Devel] Writing an IEEE 802.1BA (AVB) compliant network backend for Jack2

On Mon, Feb 28, 2011 at 07:59:01PM -0600, Duncan Gray wrote:
> I sat on the IEEE1788 standards committee when we were working on
> the timing portion of the spec and the beginning of the
> zeroconf-like discovery protocols.
> 
> To implement AVB, the intention (as far as Jack would be concerned)
> would be to get a NIC card that will most definitely implement the
> timing protocol. A consumer app that only does streaming is the
> "killer app"; and that was the only concern of Broadcom and Marvell
> -- who were major participants. This does not concern itself with
> latency, but rather with delivery. These apps stream with virtual
> timing from disk. Then the reproduce to iPods that will recover
> timing as cheaply as possible to achieve robust buffering with
> fairly low jitter playback.

i dont really understand this.
you mean streaming from harddisk to multiple endpoints,
all playing phase synced ?

with soundcards that generate their own clocks, and dont allow for rate
control ?

if one allows 3ms of diff, we can do this with netjack for quite some
time. 3ms is not relevant for comsumer applications imo.

if the soundcard allow software to gradually adjust the clock, we could
do this without resampling.
the problems start when there is packet loss and high jitter.
(such as an internet connection over the atlantic or somthing, here it
gets interesting.)


> 
> The anticipated audio app (consumer or pro) is that a VERY SPECIAL
> Audio NIC would be created that would buffer the stream and present
> it to the hardware with a strict-timed interrupt and look like an
> audio card. That card has an analog Phase-Locked-Loop controlled by
> the AVB (which is a derivative of IEEE 1588) and the timing
> information in the stream control of IEEE 1788.

you mean an audio nic in a computer ?
or in the embedded audio soundcard ?

> 
> Such NICs will become available on a very long schedule, and a
> company called Lab-X can point you to vendors leading the way.
> Perhaps someone from the Jack core crew should speak to Lee Minich
> at Lab-X about a push to open some for driver work. There is also an
> industry alliance for AVB, AVnu (Akin to the dreaded Firewire
> industry alliance.)

well... there seems to be some silicon out there....
ptp patches seem to be ready for mainlining. and will probably hit the
tip tree soon.
http://www.spinics.net/lists/arm-kernel/msg116310.html

with a reasonably good ptp timer in the kernel.
this is all easy stuff.


-- 
torben Hohn

1298951192.17392_0.ltw:2,a <20110301034548.GC23120 at siel dot b>