Re: accidental revert of Presonus 1824c quirk ?

[Roy Vegard Ovesen <roy.vegard.ovesen@gmail.com>]

On Fri, Jan 09, 2026 at 01:21:38AM +0100, fenugrec@mail.com wrote:
> That is so strange ! At least we're running the exact same system & kernel so we can rule out a few things .
> 
> I wonder if pulseaudio/pw settings could have an impact on the hopping between altsettings ?
> I'm not running pipewire, and in pulse's pavucontrol I had the presonus "profile" disabled.

Normally I'm running pw, but for this testing I have stopped pipewire completely
and use alsa directly. So far I have observed:

- Reaper, Ardour and arecord are working fine.

- When testing arecord I have to use -D plughw:S1824c to get direct control of
the device. If I use -D sysdefault:CARD=S1824c it always uses sampling rate 176400
for the device and, I assume, converts in software to the sample rate that I requested.

- By monitoring USB traffic with Wireshark I see that when for example I run arecord
it first checks and sets the clock selector, then it checks and sets the sample
rate, next it sets the interface with altsetting according to the sample rate.
When recording is done it sets the interface with altsetting to 0.

I'm wondering if one way to make the 1824c panic is by setting an invalid
sample rate and interface/altsetting combination. For example setting
sample rate to 96000 and interface/altsetting to 1/1 for playback
and/or 2/1 for recording. Are you able to monitor USB traffic when
arecord fails and check if it tries to set an invalid sample rate
and interface/altsetting combo?

So far I have not been able to break the device in this testing session,
but I will crack on.

-- 
Roy Vegard