ModemManager and MQTT messages over DBUS

Mohamed Aouadhi med.aouadhi at
Sun Apr 16 00:47:43 UTC 2023


I am using a Quectel EC21 modem, connected to an imx6ul soc via usb (UART
is also available), everything works fine and I have connectivity without

So my usecase is putting both the cpu and the modem, and I am able to do
that, but the wakeup should be from a remote MQTT message coming from my
server which will wakeup the modem first, that in turn wakeup the cpu using
the RI pin.

I have played around with this and it is only possible if I use the modem's
MQTT stack, as it will maintain the TCP connection even in sleep mode. I am
configuring the MQTT endpoint using AT commands (through mmcli --commands).

The problem is that I am not able to receive the messages when subscribing
to a topic, even though I know the message arrived (I can see the raw data
when putting modemmanager in Debug mode).

So my question is, is it possible to receive the MQTT URCs (+QMTRECV for
example) over DBUS so that my application could handle them after wakeup,
and if not what path should I follow ?

Note:  I tried probing the USB AT interface for incoming URCs but I wasn't
able to receive them, probably because modemmanager is concurrently using
it as well ?

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