Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I am running Debian on an Embedded system and am trying to use minicom to periodically get the signal strength of my USB EVDO modem using the AT+CSQ command.

When the modem is not connected, I can simply use minicom to connect to the port and execute this command. However, when the modem connects to the network, commands in minicom no longer work (ie. nothing happens or is echoed to the screen).

Any assistance with obtaining the signal strength while connected is appreciated.

share|improve this question

There are two ways to achive this:

If your mobile device provides more than one serial port (/dev/ttyUSB1 or /dev/ttyACM1 for example) you could use this one to query the signal level.

if you only have one serial, you have to put more effort into it and use a GSM 7.10 Serial Port Multiplexing. A implementation can be found at;a=summary

There is also a Debian package in Squeeze for gsm0710muxd,m see

hth, cheerio Steve

share|improve this answer
My USB modem is connected to /dev/ttyACM0 on my system. The system also has ttyS0 and ttyS1 but I assume those are for the RS-232 connections. The modem only has one port. I'm not sure I follow your logic about having multiple ports. – kittyhawk Aug 18 '10 at 19:42
Many GSM USB Modems like Option GT380 or Sierra Wireless MC8790 provides more than one serial line. Consider to use a device which provides more than one serial interface, or use the multiplexing. – Lairsdragon Aug 18 '10 at 20:10

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.