E3372h-325 does not work on primary port

There is just another alternative for E3372h. It is sold as "Brovi USB LTE modem E3372-325".

  Hardware |         manufacturer: ZOWEE TECHNOLOGY (HEYUAN) CO., LTD.
           |                model: E3372-325
           |    firmware revision: 3.0.2.61(H057SP7C983)

USB VID:PID 12d1:155e

It creates 3 virtual UARTs and they are labeled by udev rule 77-mm-huawei-net-port-types.rules as follows

• 1. ID_MM_PORT_TYPE_AT_PPP
• 2. non AT port
• 3. ID_MM_PORT_TYPE_AT_PRIMARY

The problem is that the firmware is complete rubbish and the 3rd port is broken. It does not follow any communication standard. It somehow responds to AT commands, but only some of them, and it's all in the wrong format, wrong line endings, etc. I have tried sending several AT commands to this port to get it to behave, but it does not help. So, of course, ModemManager is confused and can't understand any response from this modem.

What I have tried was to switch these labels in the udev rule

SUBSYSTEMS=="usb", ATTRS{bInterfaceClass}=="ff", ATTRS{bInterfaceSubClass}=="02", ATTRS{bInterfaceProtocol}=="01", SUBSYSTEM=="tty", ENV{ID_MM_PORT_TYPE_AT_PPP}="1"
SUBSYSTEMS=="usb", ATTRS{bInterfaceClass}=="ff", ATTRS{bInterfaceSubClass}=="02", ATTRS{bInterfaceProtocol}=="02", SUBSYSTEM=="tty", ENV{ID_MM_PORT_TYPE_AT_PRIMARY}="1"

to these (swapped the ID_MM_PORT_TYPE_AT_PPP and ID_MM_PORT_TYPE_AT_PRIMARY)

SUBSYSTEMS=="usb", ATTRS{bInterfaceClass}=="ff", ATTRS{bInterfaceSubClass}=="02", ATTRS{bInterfaceProtocol}=="01", SUBSYSTEM=="tty", ENV{ID_MM_PORT_TYPE_AT_PRIMARY}="1"
SUBSYSTEMS=="usb", ATTRS{bInterfaceClass}=="ff", ATTRS{bInterfaceSubClass}=="02", ATTRS{bInterfaceProtocol}=="02", SUBSYSTEM=="tty", ENV{ID_MM_PORT_TYPE_AT_PPP}="1"

After this change, ModemManager detects the modem correctly, I got the WAN interface with CDC-NCM with IP address.

I'm sorry, I can't test the modem further now, so I don't know if the provided network really works. I have also used the older ModemManager 1.20.4 available in Debian, but no relevant change has been made to the Huawei plugin source code since then, so I assume the problem is still present with the latest ModemManager.

I will certainly continue to investigate this modem, test the whole functionality, test with newest ModemManager version, but for now ....

Primary purpose of filling this issue is

• document the behavior of the E3372-325 with possible workaround
• ask what to do next. If my assumptions will be correct, should I propose a patch to 77-mm-huawei-net-port-types.rules doubeling the lines - once for PID!=155e and once for PID==155e?