I'm attempting to setup a Siemens TC35i GSM Modem with my Raspberry PI using an USB to RS232 adaptor. http://www.abcproducts.com/abc-products-rs-232-usb-to-9-pin-db9-serial-adaptor-cable and create a web interface with php-serial.)

I'd much rather use serial, however for some reason the GSM modem does not seem to receive any data (although it is being transmitted).

The USB to RS232 seems to work fine for the most part, until however I reboot / cycle my Pi.

If I plug my USB device in, the modem lights up nicely and access /dev/ttyUSB0 through a web browser and / or minicom without any problems and can do so for days without any issue.

As soon as I restart or cycle my Pi however, it will not work unless I unplug the device, then plug it back in again.

This is not always ideal... So I have been looking for workarounds - specifically this usbreset C script (https://gist.github.com/x2q/5124616) - which I have set to run on boot.

This almost resolves my issue... However it requires me to start up minicom, before it will send SMS again.

Ideally - I'd like to be able to resolve these issues on boot so if I want to use the GSM modem, I won't have to complete steps a, b, c and so on.

Does anyone have any thoughts as to why this might be happening? FYI - I also tried using ruby-serialport - same results.

  • Can you paste the output of dmesg somewhere ? Perhaps there are some errors when booting up that could help pinpoint the issue. – Lawrence Nov 4 '13 at 4:07
  • Hi Lawrence - it's quite long so I will add a link to the output instead. rpi.linkpc.net/stackoverflow/dmesg.output Thanks. – ash Nov 5 '13 at 6:10
  • Did you unplug the USB Serial device when you pasted that dmesg output ? Are you using a Powered Hub ? – Lawrence Nov 6 '13 at 12:20
  • No, the USB serial device was still plugged in when I pasted the dmesg output and had only just been rebooted. I'm not using a Powered USB hub no - happy to purchase one though if required - thanks for your help Lawrence. – ash Nov 7 '13 at 7:17
  • I would start with that. The last few lines of the dmesg output show the device disconnecting and then reconnecting, perhaps that hiccup is causing the issue ? Just a wild guess here though ! – Lawrence Nov 7 '13 at 13:07

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