[linux-audio-dev] Linux Alsa Audio over 1394 - a Thesis

[Steve Harris]

On Wed, Feb 26, 2003 at 11:17:31 +0100, Martijn Sipkema wrote:
> > > I'm not sure, but it seems the audio transport over FireWire does not
> > > deliver a constant number of frames per packet. Does this mean that
> > > JACK cannot support FireWire audio without extra buffering?
> > 
> > ISO packets are a fixed size, so there will be a constant number of
> > frames per packet.
> 
> No, I don't think so. The packets are a fixed size and they are sent at
> a fixed interval which means the number of samples per packet will
> differ by one. That what it says in the paper. And that is what JACK
> won't support properly because it is considered a 'broken' design.

The bottom level packets are sent at fixed time intervals (obviously,
corresponding to the frame clock of the bus), but these packets are tiny
and you get millions of them per second. A useful packet of audio data
will be made up of a bunch of these.

According to the mLAN spec you need a buffer of around ~250us (depending
on format) to collate the packets.

- Steve