The Chromium Projects

Search this site

Except as otherwise noted, the content of this page is licensed under a Creative Commons Attribution 2.5 license, and examples are licensed under the BSD License.

Debugging 3G

Contents

  1. 1 Communicating directly with a modem with the AT command set
  2. 2 A notable exception:  Gobi Modems
  3. 3 Using minicom
  4. 4 Collecting Additional Logging
  5. 5 Testing Download Speeds

Communicating directly with a modem with the AT command set

Most modems support AT commands which control the modem and query for information.   On a Chromium Notebook you can use the socat command to communicate with the modem.  You need a machine with a test image installed (or you can use gmerge socat if you are familiar with the dev server) .  For example:
  • Type ALT-CTL-T to enter the crosh shell.
  • Type shell to enter the bash shell
  • Figure you which usb device to use with: ls /dev/ttyACM* /dev/ttyUSB*
  • Stop modem manager if it is running: sudo stop modem-manager
  • Type sudo socat - /dev/ttyACM1,crnl or sudo socat /dev/ttyUSB0 to communicate with the modem
  • Ensure that the modem is enabled with the command:  "AT+CFUN=1"
For example:
crosh> shell
chronos@localhost / $ sudo stop modemmanager
chronos@localhost / $ ls /dev/ttyACM* /dev/ttyUSB*
/dev/ttyUSB0 /dev/ttyUSB1 /dev/ttyUSB2
chronos@localhost / $ socat - /dev/ttyUSB1
ATZ
OK
AT+CFUN=1
OK
ATI
Manufacturer: Qualcomm Incorporated
Model: ......
Revision:....
ESN: 0x80d...
+GCAP: +CIS707A, ....

chronos@localhost / $
Depending on the modem, you can try different AT commands, e.g. "AT+CGMI", "AT+CGSN", etc. 

A notable exception:  Gobi Modems

While modems based on the Qualcomm Gobi chipset support AT commands, Chromium OS uses the Qualcomm connection management API to control these modems. 

Using minicom

One can also use minicom to communicate with the modem.  This program is available in test images (or you can use  gmerge socat if you are familiar with the dev server) .
  • Type ALT-CTL-T to enter the crosh shell.
  • Type shell to enter the bash shell
  • Figure you which usb device to use with: ls /dev/ttyACM* /dev/ttyUSB*
  • Stop modem manager if it is running: sudo stop modem-manager
  • Type sudo minicom -s
  • Ignore, "WARNING: configuration file not found"
  • Use the down arrow key and enter to choose the menu Serial port setup
  • Type A to edit the Serial Device, changing it to /dev/ttyACM1 or /dev/ttyUSB1
  • Press enter to return to the top level configuration menu
  • Use the arrow keys and enter to select Exit which will exit configuration and let you communicate with the modem.
  • Use CTRL-A x to exit and CTRL-A z for help

Collecting Additional Logging

Restart modem manager and run it manually with additional logging enabled.
localhost test # cd ~chronos/Downloads
localhost test # script
localhost test # stop modemmanager
localhost test # modem-manager --log-level=DEBUG &

when done, exit the shell started by the script command, and analyze the ~chronos/Downloads/typescript file.

Testing Download Speeds

Chromium images include the sftp client, and also wget and curl for downloading.  If you have a test build, it contains iperf too.  You will need to enable developer mode on the platform before you are able to access the shell. 
  • Flip the dev switch to enable developer mode.
  • Reboot the system
  • Wait for system to wipe stateful partition.
  • When booted, press ATL-CTL--F2 (right arrow) to enter shell
  • Use username chronos or root. No password necessary.
  • You can now use sftp, curl, wget or iperf for testing performance.