Re: Sending commands to device while gpsd is running

[Gary E. Miller]

Yo Filip!

I'm replying to the list.  I only take offlist email from paying
clients.
 On Thu, 30 Dec 2021 23:28:14 +0100
Filip Kubicz <filip@kubicz.engineer> wrote:

>  > You are skipping a lot of details.  What version gpsd?  How are
>  > you starting gpsd?  Are you using the "-n" option?  Was gpsd
>  > running when you did the below? 
>  >    
> 
> gpsd 3.21. I understand that I should update to 3.23.1 whenever
> possible.

Yup.  A lot of "Quectel Querks" fixed in the newer version.

> You are right, there is no -n option. I'll add it to allow gpsd to
> get the data before the client connects.

It does a lot more than that.  Just do it.

> In the above situation, both
> gpsd and client are running. Command in this case is
> "$PQTMCFGEINSMSG,1,1,0,0,10*3F\r\n". Which may not be correct NMEA,
> but it's only for the receiver. Not for gpsd to worry about.

Yes, but gpsd has to worry about the response.  Not sure what gpsd
would do with $COMMANDACKOK.

>  > > When I just send the command over UART, the command succeeds and
>  > > the device sends back $COMMANDACKOK*16   
>  >  
>  > Which, of course, is invalid NMEA...  We can deal with that
>  > "querk" later. 
>  >    
> 
> In this case it doesn't matter if this is valid NMEA, because gpsd
> doesn't need to parse it.

Yes, and no.  If it confuses the packetizer, then there will be problems.

> Best case would be to let the client
> program receive it. But probably it's not that simple, as gpsd would
> have to know that it should just pass certain commands, and parse all
> the other usual NMEA sentences.

gpsd passes back all receiver NMEA already.  Not sure if that is
detected as NMEA.

>  > > What would be the best way to send a command to a device while
>  > > gpsd is running?   
>  >  
>  > Besst depends a lot on what language you prefer.  gpsctl works, or
>  > you can code up a bit of Python, C, etc.  The protocol is simple. 
>  >    
> 
> I have a Python client, which does session.stream(gps.WATCH_ENABLE |
> gps.WATCH_NEWSTYLE) and then session.next(). From what you say I
> guess you mean using gps.send()? Isn't it "Deprecated and unstable"
> according to https://gpsd.gitlab.io/gpsd/client-howto.html ?

gps.send() in Python is not gps_send() in C.  Different animals.


> I don't want to do any of the magic that gpsctl performs here:
> gpsctl:PROG: switching to match packet type 1:
> $GNRMC,105549.43,V,,,,,,,301221,,,N,V*11\x0d\x0a [...]
> gpsctl:PROG: => Probing for Garmin NMEA

Nor will you have to, once "-n" is working.  That is not even gpsctl, that
is from libgps.

> I only want to shuttle a command to the receiver over UART, without
> competing with gpsd for the serial port access. I can use python API
> or command line.

If you look at ubxtool, it does a lot of gps.send().  Pretty easy
once you have the boilerplate set.  or gpsctl.

>  > > The commands are NMEA-like text. The commands are 
>  > > independent from the daemon operation.   
>  >  
>  > Yeah.  "NMEA like".  Just enough like NMEA to confuse things.  A
>  > lot. 
> 
> That's another story, that I will add support in gpsd for parsing
> position from $PQTMINS message. But let's leave it for now and take
> care of the commands first.

If you do that, send it here, and I'll add it to drivers/driver_nmea0183.c
Another "Quectel Querk".  You will find many more of those...

IF you  have a raw capture with some $PQTMINS then send it here.  That
can be used for a regression test and to validate its decode.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        gem@rellim.com  Tel:+1 541 382 8588

            Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin

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