fibocom: Minimum PDP context ID

[Sven Schwermer]

Hi Aleksander,

On 3/29/22 10:59, Aleksander Morgado wrote:
> If you used QMI, then the Modem3gpp.SetInitialEpsBearerSettings()
> method would end up modifying that CID=1.
> But that doesn't mean you cannot change them using the profile manager
> APIs also. When using QMI, you can do both things, although if your
> plan is to change the initial EPS bearer settings, you should better
> use the specific method for that. The fact that you can use the
> profile manager APIs is just a side effect of having one profile
> associated to the initial EPS bearer settings, and ModemManager will
> not attempt to hide that from the user. We could improve all this and
> allow the profile management APIs flag specifically which profile is
> used as initial EPS bearer settings, e.g. by flagging it with
> MM_BEARER_APN_TYPE_INITIAL (if we're not doing it already! I recall
> thinking about adding that but not sure if I did).

Unfortunately, QMI doesn't seem to be an option. Even though, the MA510 
has a QMI USB configuration, it's impossible to bring up the connection 
with that. Also, it's not officially supported.

Beside the initial EPS bearer issue mentioned before, the MA510 only 
seems to really work with CID=1. Whenever ModemManager configures a 
context with CID!=1, e.g. CID=2, the subsequent +GTRNDIS=1,2 works OK 
and querying the RNDIS state confirms that it used CID=2. However, the 
periodic bearer connection checks using +CGACT? returns

+CGACT: 1,1
+CGACT: 0,2

Which marks the bearer intermediately as not connected and the ECM 
connection is torn down on the host. Querying with +CGCONTRDP confirms 
that the modem is actually only using CID=1.

This leads me to wonder what's the best way to force ModemManager to 
always use CID=1 for this particular modem model? Any ideas?

Best regards,
Sven