Re: Using screen to talk to modems via AT commands

On Mon, 17 Apr 2017 08:00:01 -0700
Tim Harvey <tharvey-UMMOYl/[email protected]> wrote:

> Greetings,
> 
> I've often asked users I'm helping with modem support on Linux to use
> GNU screen to issue AT
> commands to modems to get their details (ie ATI), however I've noticed
> this doesn't work for me anymore on perhaps newer modems and I'm
> guessing its related to a missing stty setting relative to CRLF.
> 
> So the following works from bootup on an MC8790 for example:
> # echo -e "ATI\r\n" > /dev/ttyUSB3
> # cat /dev/ttyUSB3
> ATI
> Manufacturer: Sierra Wireless, Inc.
> Model: MC8790
> Revision: K1_0_2_8AP C:/WS/FW/K1_0_2_8AP/MSM6290/SRC 2008/09/17 14:00:22
> IMEI: 352974021856935
> IMEI SV: 3
> FSN: D661380183210
> 3GPP Release 6
> +GCAP: +CGSM,+DS,+ES
> 
> 
> OK
> ^C
> 
> However if I use 'screen /dev/ttyUSB3 57600,cs8' I find that AT
> commands are never recognized - I get no response from the modem as if
> it didn't catch the right line termination.
> 
> Any ideas as to what's going on here and how I could use screen and/or
> stty to resolve it or what the proper stty settings are to avoid this.
> 
> Regards,
> 
> Tim

Hey,

what version of screen do you use and which distribution?

if it worked before, first thing which would help is narrowing down working/not working version
( https://ftp.gnu.org/gnu/screen/ )
And then perhaps using git bisect to narrow it down to specific change
(use screen-v4 branch for that http://git.savannah.gnu.org/cgit/screen.git/log/?h=screen-v4 )

Cheers,
Amadeusz