30 Mar
2019
30 Mar
'19
7:37 p.m.
On 30.03.19 04:52, Paul Davis wrote:
On Fri, Mar 29, 2019 at 4:57 PM Max
<abonnements(a)revolwear.com
<mailto:abonnements@revolwear.com>> wrote:
Fernando Lopez-Lezcano discussed the pitfalls of using the MOTU AVB
external audio interfaces with Linux in his paper [1] and also in the
keynote at LAC-19.
Let's start another thread around this card.
Fernando mentioned that different firmwares expose different issues,
but
downgrading is possible. Issues are:
1. Channels are not persistent and swap around.
2. Total number of channels has been reduced in newer firmwares.
3. An endless card acquisition loop between Jack and Pulseaudio
caused by
the long time the card needs to switch sampling rate.
4. Seemingly erratic behavior, opening the device fails, fails again,
again, then works suddenly.
issue 4 is not resolvable via firmware changes. it seems part of the
device design.
I think 3 and 4 may actually be the same issue.
I have a couple of questions and experiences.
Is there a table of the firmware versions somewhere (linuxaudio wiki?)
which tell me which versions has which features (removed)?
fernando mentioned a post on "linux musicians" which describes each one.
for reference, I guess the thread is this one:
https://www.linuxmusicians.com/viewtopic.php?f=6&t=18046
It's a rather long thread with some interesting tidbits here and there.
Someone even wrote a test program, but one has to be signed in to see
attachments on this forum.
Three takeaways from this thread:
1. AVB might be supported by the kernel at some point, which would allow
to use the AVB interfaces without the USB connection.
See: https://github.com/L-Acoustics/avdecc for a multiplatform
implementation.
2. Firmware 1.2.8. is the last one which provides 64 channels via USB
Class Compliant, downgrade to this version if more then 24 channels are
needed.
The old firmwares are downloadable here:
http://motu.com/techsupport/technotes/firmwarechangelog/
3. There is no way to change the number of channels through ALSA or via
the configuration panel of the web-interface. It's static.
Are all the Class Compliant models having the same
quirks as listed
above? For example the
MOTU UltraLite AVB versus the MOTU 624 AVB?
Is it possible to use the Thunderbolt port to connect the card to a
Linux computer?
Why can't I tell ALSA to use only the first 2, 4 whatever channels of
the device? I can only open the device if all channels are
connected. Is
this always like that or is that a limitation of MOTU's implementation?
ALSA doesn't work that way. You open a device. You tell it how many
channels you want to use.
That's what I thought, but apparently it only succeeds to open an ALSA
device if the number of channels match.
On my laptop with only one USB bus, If I connected
the MOTU 624 AVB
and
then another high speed usb device, the computer could not connect the
later, because the MOTU reserved all the bandwith for itself.
Connecting
the other device and then the MOTU worked.
this is correct, and likely a sensible design choice. others may
disagree. i actually threw away a webcam because i mistakenly believed
that it was no longer working (because of this issue).
That's hilarious. I only stumbled upon this issue by looking at dmesg
output because of something unrelated. Thankfully the dmesg output is
quite verbose and clear about what's going on.