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Re: [gpsd-dev] gpsd - AT command control on modems

From: Luca Weiss
Subject: Re: [gpsd-dev] gpsd - AT command control on modems
Date: Sat, 13 Jul 2019 18:32:11 +0200

Hi Gary,
sorry for not replying earlier but I didn't get your reply (or any of the 
other replies here) into my inbox, so I just now accidentally saw in the 
webinterface that there have been replies. I'm not subscribed to the list, so 
maybe you used "Reply" instead of "Reply all" ?

Anyways, replying to your reply:

> Dunno why you would use the socket AND specify the device.

I copied the command from somewhere; I'll use the service file in Alpine for 
launching gpsd next time, it was just a quick way to get it working.

> Afterwards, not before?  USB2 not USB1?

Doesn't matter, if before or after from what I can tell.

Yes, ttyUSB2, because that's used for "AT command communication" and ttyUSB1 
is used for "GPS NMEA message output" according to a document from Quectel.

> Don't bother,  That would be very hard.  Just do:
>         # echo ""AT+QGPSEND" > /dev/ttyUSB2

What's bugging me there is that the modem is still doing all the hard work 
with GPS even when nobody is using the gps coordinates and is probably using a 
lot of energy (remember, it's a phone with a battery^^).

> > I've also seen that ofono provides a "location reporting api"; and
> > there's also modemmanager which provides seemingly the same
> > functionality;
> No idea.  Might be soemthing easy and standard, might be bizarre and
> proprietary.
> we would need some doc to know.

The modem has a lot of weird assistance data stuff that I don't quite 
understand, partly because - as far as I understand it - some tool is needed 
to upload the assistance data (which can be downloaded from a website as a 
file) to the modem and then some AT commands have to be run to use that file.

But other than that, the only important commands for the GNSS part of the 
modem are:

AT+QGPS=1 for turning ON the GNSS
AT+QGPSEND for turning OFF the GNSS

The command manual can be found at [1]

Also replying to Paul:

> How about adding that to /etc/gpsd/device-hook (see man gpsd)?

Does the deactivation hook get called when no application is using gpsd 
anymore - which would fit the power requirements mentioned above? Thanks for 
the pointer!



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