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Re: Questions about decoding subframe messages (ublox F9P)

From: Curtis Olson
Subject: Re: Questions about decoding subframe messages (ublox F9P)
Date: Tue, 26 May 2020 22:07:53 -0500

On Tue, May 26, 2020 at 4:33 PM Gary E. Miller <address@hidden> wrote:
u-blox port numbering is random, and badly documented.  You'll need to
run experiments to figure what is what.

On windows you get to play guess the com port I suppose, but on LInux it pretty consistently comes up as /dev/ttyACM0 ... unless I have gpsd running and give the port over to virtualbox, and then give it back and have forgotten to kill gpsd, at which point ACM0 is tied up so it instantiates itself as ACM1.
> also have Windows 10 in a virtual box so I can run u-center and talk
> to the receiver that way.

Can't help you there.

It's not as bad as it sounds, except u-center is really weird and I'm still not sure I have it completely figured out.
Dunno which port is the xbee port.

I had this figured out a few months ago and got the gps location to the xbee and relayed off as a proper mncors request and then the web correction messages started coming back and the gps got to the point of a floating fix or some thing, but I was indoors through a gps repeater so I didn't get too concerned about not having a full locked in rtk solution.
As you can hear, many people new to the F9P, and friends, doing
different hings in different ways.  Hard to separate them in my

Now that I'm watching the mailing list, I can see you are involved in several deep threads ... I appreciate all the guidance and knowledge!
I took a longer look at the F9P doc.  The ONLY way it sends subframes
is the UBX-RXM-SFRBX messages.  Which you are getting.  gpsd does not
yet decode those, as they are new.  gpsd only sends you the raw messages,
the ones that you have been seeing.

Ok, this was my read too from the F9P doc.  So ok, good, part of all this is that I really wanted to make sure I wasn't missing something obvious.
Until someone updates the gpsd decoder to handle RXM-SFRBX that is
a good as it gets.  Other drivers can decode the subframe from other
vendors, "just" needs some plumbing.

I see the driver_ubx.c code, and see that it does something with RXM-SFRB messages (not in ublox8/9) but doesn't specifically handle the RXM-SFRBX message.  It's getting late tonight, but if I can get my brain cells stirred around enough in the morning, maybe I'll take a crack at adding some plumbing, see how far I get.

Nothing you want to do will be easy.

I ran my autonomous boat project this evening and all it did was go in circles, so you might be on to something there. :-)
And it does, and you are seeing them.  Understanding what that hex means is a hole 'nother level of hurt.

 One step at a time ... I've already learned way more than I wanted to. :-)

Thanks again for all  your help,

Curtis Olson
University of Minnesota, Aerospace Engineering and Mechanics, UAS Lab

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