On 3/15/21 9:37 AM, Fernando Lopez-Lezcano wrote:
...
Motu's original firmware for the AVB interfaces was upgraded early on to
be able to do up to 64 channels on usb2 (which I have been using
extensively). It was latter downgraded to just 24. I started a ticket
and was told that they were having (unspecified) problems with it.
There is a hack that makes it possible to connect the linux usb driver
to the proprietary usb endpoints of the audio interface and thus run at
up to 64 channels (for 44.1/48KHz sampling rate, of course). This
involves kernel patches and also manually switching the interface to the
proprietary mode through an hhtp/json command (otherwise it just uses
the class compliant endpoints[*] after you plug it in). This very long
thread has information about this:
https://linuxmusicians.com/viewtopic.php?f=6&t=18046&sid=3deb30fa5d04d5240741640f329aa2ea
< just for the record, latest update >
I am using one of the solutions in that thread successfully (so far :-),
see pages 40/41 for the latest. Running in an 8M with the latest firmware.
"Drumfix"s modified ua101 driver with matched kernel patches and
blacklisting (as outlined in the thread) seems to work just fine in
proprietary mode (64 channels at 48KHz sampling rate). No channel
hopping or buzzing high frequency artifacts.
A caveat: this solution does NOT really work if the kernel is a realtime
preemption kernel (patched with the RT patch and configured with
CONFIG_PREEMPT_RT). Well, it works but the video performance is really
bad in my system, choppy with periodic long lags (~> 0.5 sec) in the
GUI. This is apparently due to the many context switches happening in
the RT kernel because of the high rate of interrupts.
It DOES work fine in a "normal" kernel configured with CONFIG_PREEMPT=y
(what drumfix advised), which is what I am currently using. I can run
jackd at 128x2 which is not bad (with a few xruns if I switch desktops
and all that, otherwise fine).
...
[*] I imagine there is some initial handshake that tells the card that
the motu driver is accessing it, and that is obviously missing in linux
That is indeed the case. The aforementioned solution still requires a
curl command to switch the motu to proprietary mode, but the recent root
hack has enabled someone to figure out the usb commands used to do that,
so this may be incorporated into the driver in the future.
Best,
-- Fernando
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