Re: [Jack-Devel] Merge Firewire Device

Hi Tim

On Sat, Jan 05, 2013 at 02:49:31AM -0500, Tim H. wrote:
> I found the below documentation which explains how to "aggregate"
> multiple Audio devices:
> 
> http://jackaudio.org/multiple_devices
> 
> My question is if anyone has an experience with this and my specific
> device.  I have two Presonus Firebox's which have essentially 4
> inputs and 6 outputs each.  I'm looking to merge two of these
> firewire devices for a recording project I have coming up ...

Since the two devices you're looking at are both firewire interfaces they
will both be managed by the "firewire" jack backend (not ALSA).  This uses
FFADO (www.ffado.org) to interact with the device.  Theoretically, if there
are multiple supported firewire devices found by FFADO, FFADO will aggregate
them automatically.  The inputs and outputs from each respective device will
be available for use via jack and you should be able to accomplish your
task.  There shouldn't be a need to utilise the information at the link you
provided since the aggregation is taken care of at the FFADO level.

There are a few significant caveats.  The first is that the code which
manages the multiple devices hasn't seen a huge amount of testing.  It has
been successfully used by a few people, but due to differences between
interfaces these past experiences can't be taken to mean that it will work
with two Fireboxes.  As far as I am aware, no one has tried FFADO with more
than one Firebox before, so the best thing to do would be to test it and see
what happens.

Secondly, the reports we (FFADO) have received indicate that while FFADO can
theoretically cater for unsynchronised devices, the resulting system is more
stable overall if the two devices are clocked synchronously.  This can be
accomplished on many interfaces by linking work clocks together.  However,
from memory the Firebox doesn't have word clock I/O.  One trick you can use
in this case is to connect the SPDIF output from one device to the SPDIF
input of the other and arrange for the second Firebox to sync to SPDIF. 
This should effectively lock both devices to the same clock.

> Any advice, or tips you can provide would be helpful.  I plan on
> hooking these up Monday for some initial testing.

The best advice I can give is to try it and see.

It should be noted that if trouble is encountered, it is probably more
applicable to post your findings to the ffado-devel list because it will
more than likely be the FFADO code which needs to be fixed.  Details about
ffado-devel can be found on the FFADO website (www.ffado.org).

> Side question:  The device has 2 firewire ports on the back.  I know
> Presonus doesn't auto-support daisy chaining on this device.  But,
> would the other port act as a Firewire "through".  Else, I'll have
> to hook up a second firewire PCI card.

It would be interesting to know why Presonus don't support the daisy
chaining.  Again, try it and see if it works.  FFADO itself won't care. 
Since two Fireboxes won't go close to consuming all of the available
Firewire bus bandwidth, the only issue I can see is if there is something in
the Firebox hardware or firmware which precludes this configuration from
working.

Regards
  jonathan

1357376325.22797_0.ltw:2,a <20130105085824.GA11445 at marvin dot atrad dot com dot au>