mjhjmtu

We are using the 3G modem Telit LE910-NAG (I'm aware that it is not recommended for new development but for now I cannot change it). I’m using it on a Linux OpenWRT platform.

I followed the direction from the document CE/DE/LE910, HE/LE920 Linux USB Driver - User Guide (https://www.telit.com/wp-content/uploads/2017/09/Telit_Linux_USB_Driver_User_Guide_CE_DE_LE910_HE_LE920_r0.pdf) and add the driver option for serial port and qmi_wwan for network adapter.

Device USB ID is 0x1201 and I have 5 ttyUSBx listed when the modem is on.
The document mention:

please refer to the proper AT commands User Guide for port arrangement description.

But looking at the following: http://ec-mobile.ru/user_files/File/Telit/telit_le9x0_at_commands_reference_guide_r14.pdf I didn’t find serial port arrangement.

1) So, can you help me understand how the port are mapped and what port I should use to configure my modem?

My second issue is about how to configure the serial port to communicate with the modem. I can use the port ttyUSB2 with minicom without issues. But we need to use it in a script with only echo and cat (the board does not have a lot of space).
Echo works find but when I try to read the data with cat I have some weird results (line or character duplicated or missing) and cat is handling (need to kill it with ctrl+Z).
I try different configuration with stty (stty /dev/ttyUSB2 raw, ssty /dev/ttyUSB2 -echoe -echo -echok) but without success. Also, when I try to set the serial port speed it fail:
root@OpenWrt:~# stty -F /dev/ttyUSB2 115200
stty: /dev/ttyUSB2: cannot perform all requested operations

There is no other process accessing the serial port and I’m root.

2) So which port should I use to do this and how can I configure it?

Thank you very much for your help.