[linux-audio-user] open source firewire

Mark Knecht markknecht at gmail.com
Sun Nov 28 13:14:27 EST 2004


On Sun, 28 Nov 2004 10:55:46 -0600, Ryan Gallagher
<ruinaudio at comcast.net> wrote:
> Guys,
> 
> Something to consider when planning to develop a firewire audio
> interface...  I'm still unable to get decent jackd/alsa performance (sub
> 50ms latency and clear sound w/full duplex) with my seemingly well
> supported USB emi 2|6.  I mean has anyone gotten decent low latency (sub
> 12ms) performance with a full-duplex USB device?
> 
> (BTW, yes I have appropriate patches applied, I'm able to get decent
> latency/performance from my onboard generic Intel Corp. 82801DB/DBL/DBM
> (ICH4/ICH4-L/ICH4-M) chip.  It did work better before jack periods were
> forced to be powers of 2.)
> 
> Anyway, to get to the point... isn't it true that firewire by virtue of
> it's similar-to-USB-nature suffers from the same limitations as USB?
> Iirc I was told that whatever limitations causing the (IMO) extreme
> suckage of USB audio on linux will be present in a firewire interface.
> 
> I'm speaking from distant memory here as I've given up on my ~$400 USB
> investment, which now collects dust.
> 
> What a shame it would be to expend effort and $$$ to find there's some
> <cat /dev/random> issue that prevents firewire audio from working
> acceptably.
> 
> -ry
> 
> 

Ryan,
   Good points to keep in mind. However, I can say that I use
DigiDesign/Pro Tools 1394 under Windows with latencies that you would
term acceptable so I know it *can* be done. Whether is can be done
under Linux is another question.

   *Most* 1394 devices under Windows use the normal Windows 1394
driver. QUESTION: Are the Linux 1394 drivers up to the task? I'm not
sure. I own 6 1394 peripherals. (3 hard drives, an external CDROM, an
external DVD and a video conferencing camera.) All work perfectly
under Windows. Under Linux 3 work, 3 do not. There are only about 5
people developing the 1394 stack under Linux. The stack has been in
development since 1999. This does not make me confident about Linux
and 1394 unless this hardware project was to undertake ensuring that
the 1394 stack gets attention from our hardware/software developers
should it need it.

   I will also raise the question 'why can't USB attain the latencies
you want under Linux?' I *think* they can be attained under Windows,
so why not Linux? Does this say something about the USB stack? USB
support under Alsa? I don't know and I'm not capable of finding out.

   Unfortunately, Alsa (as I see it, and which is probably an
uninformed view) is really only a few people. I think that there are
not enough people developing Alsa, and then developing Alsa drivers,
to ensure it works as well as the hardware specs can support.

   As background, I helped write the 1394-2000. (Small contributions
only, but I was part of the committee.) I can say with certainty that
hardware like we are talking about was contemplated in the committee
meetings. I firmly believe that this project is completely within the
capabilities of 1394. Whether we are good enough hardware and software
designers would have to be shown. On this point I am confident.

Cheers,
Mark



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