Problems with modems/Example config for QMI-based modem,

[Jakob Hasse <jakob hasse smart-home-technology ch>]

Hello,

We want to integrate different modems into our embedded system. 
Recently, our Linux-distributor decided to introduce NetworkManager. 
When we switch to NetworkManager, network connectivity via 3G/2G is 
never reliable: the connection either succeeds only sporadically or not 
at all. This happens on three types of modems from two different 
vendors. When we set up the modems manually with pppd or with a QMI test 
program, everything works fine an reliably, also automatically after boot.
Could you give me advice what steps to do to produce debug/log output to 
then come back here and have someone look at it?

Furthermore, it would be really nice to have an example configuration 
file for /etc/NetworkManager/system-connections/ to configure a modem 
with QMI connection. All the examples I had so far (seem to) only 
establish the connection with pppd.

Another problem is that it often happens that we use NetworkManager on 
devices which changes some settings and afterwards we can't even use the 
old methods to establish a connection. This is really scary since it 
basically renders our devices unusable so far. Is it possible to tell 
NetworkManager to put the device in the original state again after using it?

I also have a question to ModemManager but don't know whether I'm right 
with it here:
We want to send AT commands to the modems while they serve an internet 
connection. Normally, this is possible since the Modems all have 
multiple serial interfaces. But when using ModemManager, it locks all 
serial interfaces of the modems and we can't use them anymore. I know 
that ModemManager can send AT commands with "mmcli --command" but only 
in debug mode, so apparently not for production use. Is it possible to 
send commands another way with ModemManager or prevent it from locking 
all AT interfaces?

Thank you and All the Best,
Jakob

--
Jakob Hasse
Software Developement

E: jakob hasse smart-home-technology ch
T: +41 44 552 02 66

Smart Home Technology GmbH
www.smart-home-technology.ch