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Re: [gpsd-users] poll ubx-rxm-rtcm as shown in page 93 of zed-f9p integr

From: Gary E. Miller
Subject: Re: [gpsd-users] poll ubx-rxm-rtcm as shown in page 93 of zed-f9p integration manual
Date: Fri, 19 Apr 2019 11:28:05 -0700

Yo Svenn!

On Fri, 19 Apr 2019 19:11:20 +0200
Svenn Are Bjerkem <address@hidden> wrote:

> I am looking into code of ubxtool to look for a way to ask the gps to
> tell me about the RTCM data it has received.


        # ubxtool -p MON-COMMS

        version 0 nPorts 4 txErrors 0x0 reserved1 0
        protIds 0x0/1/5/ff (UBX/NMEA/RTCM3/None)
          Port: 0x100 (UART1)
           txPending 0 txBytes 143075741 txUsage 0 txPeakUsage 16
           rxPending 0 rxBytes 0 rxUsage 0 rxPeakUsage 0
           overrunErrs 0 msgs 0/0/0/0 reserved 0 0 skipped 0
          Port: 0x200 (UNKb)
           txPending 0 txBytes 170940265 txUsage 0 txPeakUsage 0
           rxPending 0 rxBytes 459762783 rxUsage 6 rxPeakUsage 15
           overrunErrs 0 msgs 62531/0/0/0 reserved 0 0 skipped 27
          Port: 0x300 (USB)
           txPending 0 txBytes 190703 txUsage 1 txPeakUsage 31
           rxPending 0 rxBytes 531 rxUsage 0 rxPeakUsage 0
           overrunErrs 0 msgs 29/7/0/0 reserved 0 0 skipped 80
          Port: 0x101 (UNKa)
           txPending 0 txBytes 459755279 txUsage 0 txPeakUsage 0
           rxPending 0 rxBytes 170554901 rxUsage 4 rxPeakUsage 12
           overrunErrs 0 msgs 3374/0/0/0 reserved 0 0 skipped 0

You need to check this line to see RTCM3 recception is enabled, and
where in the "msgs" data to look for it:
    protIds 0x0/1/5/ff (UBX/NMEA/RTCM3/None)

So here, RTCM3 message count will be the third field.  Then look
in "msgs" for each port.  On  the 0x0200 port:
     msgs 29/7/0/0 reserved 0 0 skipped 80

That means 29 UBX, 7 NMEA, and zero RTCM messages were "Number of
successfully parsed messages for each protocol."

Sadly the output of UBX-MON-COMMS does not exactly match the
documentation, so a bit of guesswork is required.

> gpsd log tells me that
> it relays rtcm data at regular intervals to the gps, but the RTK led
> does not go off,

I'm sure the gpsd log has a lot more to say.  What did it say?

> so I am trying to follow the data stream of the RTCM
> from the ntrip url down into the gps. I guess this particular
> easy-access poll function has not been implemented yet.

I guess you missed it.  Not that it will help much...

> u-center ntrip client is able to read the same RTCM data, feed it to
> the gps and make the LED go off (RTK float at least)

Send me the u-center code and I'll cut/paste it.

Likely not going to happen.  so maybe packet captures of both gpsd
and u-center to see what is going on.  There are a lot of undocumented
magi incantations involved...

> What I am chasing here is using two F9P modules one for rover and one
> for base. The base will use survey-in to find its coordinate, and
> then start outputing RTCM correction data to the rover. The F9Ps are
> connected to raspberry pi through usb. radio communication is done
> through 868 long range radio also connected to raspberry pi on usb.

Very common, but the common way to do it is not what you are doing.

Usually you feed the RTCM3 outport 2 of the base and feed that to
the rover.  No gpsd involvment required.

> For a start, I am using a nearby RTCM source transported by
> which is the one I fed to u-center.

Any way I could see that feed?

> Of course, u-center may have done some configuration behind the scene
> which I am not aware of. u-center tends to do that.

Yup.  Much dark magic here.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  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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