[PlanetCCRMA] M-Audio 24Ao w. updated firmware on linux nowadays ?

[Fernando Lopez-Lezcano]

On 10/26/20 10:10 AM, anders.vinjar at bek.no wrote:
> Hi everyone.

Hi,

> I've had some issues under Linux with channel swapping on an M-Audio
> 24Ao interface connected as a class compliant USB audio interface.
> 
> The internet from last year tells me this was a issue with the then new
> firmware, and at the time suggested downgrading as a solution.

If the hardware you have can be downgraded (I believe to 1.2.8+ or 
something like that) then do that and you should be fine. Regretfully 
newer hardware versions cannot be downgraded.

> Before i attempt downgrading, i'd like to ask: is anyone using such a
> card using more recent firmware, and successfully running it under Linux
> without the channel swapping bugs?

The short answer is not really.
The long answer is, maybe (and the answer is long)

There is a very interesting thread here, where I found stuff I have tried:

https://linuxmusicians.com/viewtopic.php?f=6&t=18046&sid=36bb42c1f0e44c69d3d5141b0a414621

This is mainly focused in the Ultra Lite AVB but is relevant to other 
AVB cards. Worth reading through it. There are experimental patches and 
an experimental driver in there...

I have tried and I am currently using the patch that can use the AVB 
cards using their proprietary USB endpoints instead of the regular class 
compliant endpoints (the reason for this in my case is to be able to use 
64 channels under linux and the newer firmware). This requires both a 
modified snd-usb module and the kernel itself. Once booted into that 
modified kernel the card will be recognized as before, but it is 
possible to activate the proprietary mode inside the Motu card by 
sending three setting changes through http. Once all the pieces are in 
place the card can be used with 64 channels (or 32 or 24) with the newer 
versions of the firmware.

With an RT patched kernel (5.9.1) the performance is reasonable (using 
it in 64 channel mode, I have not tried 32 or 24). I do not see channel 
hopping, but sometimes the card goes into a mode where there is a high 
frequency buzz or noise. Restarting jack usually gets rid of that. I 
have not found a definite way to avoid that entirely. I am running this 
in an 8M and an 16A (so it should behave in the same way in a 24Ao).

Sometimes the "buzzy sound" reoccurs, sometimes the audio interface can 
run for a day with no problems. Some kernel options recommended at the 
end of that thread seems to make things behave better. It would appear 
from the nature of those options that the Motu hardware is very 
sensitive to getting a completely constant and reliable stream of USB 
packets.

I also tried very briefly an experimental driver (also in that thread) 
based on the ua101 driver. This was not successful - I still got channel 
hopping. I did not try again with some suggested changes that appeared 
later in the thread...

Hope this helps....

-- Fernando