I have a sim800c usb modem to be able to send and receive sms on the router, I can't configure it correctly. I want to use smsd.
Can you guide me?

It's ok, there is a modul kmod-usb-serial-ch341 to install.

so have you tried and does it work?

yes, thank-you. It works

I encounter another problem, sometimes the modem changes ports, it alternates between /dev/ttyUSB0 et /dev/ttyUSB1 (smsd makes an error)
How can we do?

Which router and firmware version?

In what situation it change ttyUSB interface?

The modem is GL-SFT1200 version 4.14.90
After 1 or 2 days for no particular reason.

It looks like the modem is reloaded and then it create another interface.

Please try a more powerful power adapter.

I put a 27w power supply but I still have the same problem. Is it possible to fix the port?

It depends on the USB power output of the router. So if you modem is separated powered it may work better.

Unfortunately when USB devices reload the port number may just change to next available one.

Thank you for your answers,
I think there is another problem, I'm having a little trouble getting the modem to be recognized. Here is my approach, I reset the firmware without the modem, I install the ch341 module, I plug in the modem ((sim800c) and it works (with minicom or smstool3). After a reboot it malfunctions again (AT commands not recognized or port change). There is a problem that I can't understand

After reboot, does the modem load at all? i.e. it create ttyUSB ports?

Can you get the log?

I tried on a raspberry and it works (with minicom) or putty with window.
When I do the same thing with the sft1200, it no longer works correctly (the minicom outputs are not identical, it adds Call ready and sms Ready regularly), is it because of another process which is requesting it?
The log is correct :
Tue Jun 11 14:24:44 2024 kernel: [ 8629.270990] ch341 1-1:1.0: ch341-uart converter detected
Tue Jun 11 14:24:44 2024 kernel: [ 8629.279468] usb 1-1: ch341-uart converter now attached to ttyUSB0

it worked for 12 hours, then after a port change and a reboot, the modem no longer works... Do you have an idea for a compatible modem? I just want to send or receive sms (domotique).