Connect Cinterion modem with SWWAN fails with unknown error

[Sven Schwermer]

Hi again,

I did some more work and now I am able to connect manually (without ModemManager). All that’s required is the AT^SWWAN=1,1 command if the APN is already correctly configured. I checked this via AT+CGDCONT?. Note, that this only works for CID=1. After changing the APN for CID=1, the modem must be forced to re-attach since the modem auto-attaches after power-up. More on this can be found in the chapter “Attaching to LTE Networks” in AT manual. Another interesting fact is that the modem appends a string to the APN after it has attached, in my case “.mnc009.mcc242.gprs”. I’m not sure if this is common.

In order to debug the command sequence issued by ModemManager, I extracted all commands sent by the ModemManager from the debug logs incl. their timing. I then replayed them with the same (similar) timing manually from a script, i.e. without ModemManager running. I made sure that the modem was freshly booted in both cases. Curiously, when replaying the commands, the AT^SWWAN commands succeeds. This leaves me a little puzzled.

Does ModemManager issue commands concurrently? I saw in the logs both “device open count is 2 (open)” and “device open count is 3 (open)”. Could that mean that sometimes two AT commands are sent at the same time?

Best regards,
Sven
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