Using GNU screen for AT commands

[Tim Harvey]

On Tue, Apr 11, 2017 at 1:13 AM, Aleksander Morgado
<aleksander at aleksander.es> wrote:
> On Mon, Apr 10, 2017 at 10:25 PM, Tim Harvey <tharvey at gateworks.com> wrote:
>>>>> My apologies if this isn't the right place to ask this. I've googled
>>>>> around for the past couple of hours and haven't come up with anything
>>>>> concrete other than people saying to use a different app.
>>>>
>>>> Yeah, like minicom, right? ;)
>>
>> yes among others (picocom, atinout, tmux) but I see the same results
>> with minicom and picocom (and the others are not standard packages).
>> Are you using some stty settings prior to running minicom?
>
> I usually just "minicom -D /dev/ttyUSB0" for example, without any
> specific baudrate settings unless it's a real RS232 device (i.e. not
> USB). Then 8N1 is the usual default for all modems, I have never seen
> one using any other thing.
>
> Is ModemManager able to talk to the TTY? Or not even that?

Yes, ModemManager works and to debug this I looked at its code to see
what it was doing the other day:
https://cgit.freedesktop.org/ModemManager/ModemManager/tree/src/mm-port-serial.c#n1055.
I didn't see anything there that surprised me but I haven't compared
with what screen/minicom were doing.

It's rather strange... I've 'always' used screen and/or minicom for AT
commands such as ATI in the past and I can't pin down when it stopped
working. I've got a handful of sierra wireless modems that I could
swear I've talked to via screen/minicom that exhibit this. I'm almost
certain it has something to do with CRLF and the modem just not seeing
the proper termination character for its AT command interpreter.

Tim