Help on an invalid modem case

[Louis-Alexis Eyraud]

Hi,

my team and I are using for testing purposes an 3G USB modem (Huawei E352) that has an unexpected behaviour with ModemManager 1.12.10 and later stable versions (1.12.12 and 1.14.0).
The 3G modem is used as a broadband one and every time it disconnects, it encounters AT serial timeouts and is eventually declared as invalid by ModemManager then removed from modem list.

Jul 02 08:42:27.226342 tap-00006711 ModemManager[1225]: <debug> [1593679347.226334] (ttyUSB1): --> 'ATE0<CR>'
...
Jul 02 08:42:30.453896 tap-00006711 ModemManager[1225]: <debug> [1593679350.453872] (ttyUSB1): --> 'ATV1<CR>'
Jul 02 08:42:33.679831 tap-00006711 ModemManager[1225]: <warn>  [1593679353.679807] (tty/ttyUSB1) at port timed out 2 consecutive times
...
Jul 02 08:42:59.421551 tap-00006711 ModemManager[1225]: <error> [1593679379.421503] (tty/ttyUSB1) at port timed out 10 consecutive times, marking modem '/org/freedesktop/ModemManager1/Modem/0' as invalid
...
Jul 02 08:43:02.667893 tap-00006711 ModemManager[1225]: <debug> [1593679382.667880] Modem (Huawei) '/sys/devices/pci0000:00/0000:00:1c.0/0000:01:00.0/usb4/4-1' completely disposed

Only an external action (unplug/unplug, electrical action) makes it reappear, manual scan via mmcli does not.

So I have two questions:
1) Is there something in the debug logs that may explain these systematic serial timeouts?
I'm not sure ModemManager is at fault here (like some actions leading to unrecoverable errors) or the modem device is simply defective...

2) When the modem is declared invalid, is a there a way using libmm-glib to detect or be notified of such event occurrences?
The device disappearance at ModemManager and NetworkManager level is an obvious one but since it is quite a common event, we would like to know if something more specific can be observed.

Thanks in advance for the help.

Regards,

Louis-Alexis Eyraud
Embedded software engineer
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