OpenWrt: unexpected disconnect requiring manual restart of ModemManager

Aleksander Morgado aleksander at
Mon Apr 27 07:36:48 UTC 2020

Hey Enrico,

> sorry for the intrustion and for going over this again but...
> You mentioned the Librem5 and it's use of MM.


> I was wondering if I could use one of my QMI modems to do phone calls.
> I seen the voice interfaces, but audio routing remains a mistery to me even today. :)
> E see there are projects like:
> ... but, it seems it relies on the fact the SIMCOM modems exposes an ALSA-compatible PCM interface, right?
> but, is there a way to use a QMI modem as a phone? What about audio routing specifically?
> Or is this modem-specific and, does it in general require particular firmware or some hardware connected to the module for audio?

That's the key thing, you need to have the audio managed out of
ModemManager, either as a separate physical channel doing the audio
right away, or via some other way, e.g. a ttyUSB port that you could
use to route audio in userspace. In that latter case, we flag the
ttyUSB as "Audio port" with udev tags, so that MM doesn't even try to
probe it.


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