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Re: Questions about decoding subframe messages (ublox F9P)

From: Gary E. Miller
Subject: Re: Questions about decoding subframe messages (ublox F9P)
Date: Tue, 26 May 2020 14:32:42 -0700

Yo Curtis!

On Tue, 26 May 2020 16:13:57 -0500
Curtis Olson <address@hidden> wrote:

> > You also appear to be using ports 0x200, 0x300, 0x101 and 0x201?
> > What for?  How?
> If there are messages configured for the SPI and I2C ports, I suspect
> that just came from a default config?  Those aren't connected to
> anything.

IN, not out.  Coming from outside the chip.

> For all of this discussion, I am connecting up via the USB port and
> talking to it from my desktop computer (running Fedora 32 Linux.)

u-blox port numbering is random, and badly documented.  You'll need to
run experiments to figure what is what.

> 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.

> This unit is the simple rtk2b from ardusimple.  We have a cell
> network xbee (running a micropython script) and can login and receive
> virtual rtk corrections via the mncors (state of Minnesota) system.
> The xbee needs to know the receiver location in order to make a
> proper mncors request, so we need the unit configured to send some
> minimal positional info to the xbee port.  This same port is set up
> to receive the RTK correction packets.

Dunno which port is the xbee port.

> *BUT* I don't care about RTK right now ... that is some other future
> project, I don't want to convolute this thread with RTK stuff, 

As you can hear, many people new to the F9P, and friends, doing
different hings in different ways.  Hard to separate them in my

> I'm
> just explaining what we have and how it's configured.  For now we
> just want the F9P so we can get the raw/subframe messages.

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.

Until someone updates the gpsd decoder to handle RXM-SFRBX that is
a good as it gets.  Other drivers can decode the subframea from other
vendors, "just" needs some plumbing.

> Ultimately, when the system is deployed in a UAV, it will be connected
> through UART1, not USB, so that is why we had UART1 setup to output
> the same messages.  Maybe we jumped ahead assuming some of the
> intermediate stuff would be smoother sailing.

Nothing you want to do will be easy.

> I apologize, I don't think I understand this question.  The
> ublox_ZED-F9P interface document has 8 instances of "subframe".

The answer was: UBX-RXM-SFRBX, which you did enable, and is your only
option.  I failed to notice it is the ONLY way in the F9P, and not
supported yet by gpsd.

> we purchased this specific model gps because it has the
> capability of outputting the subframe messages.

And it does, and you are seeing them.  Understanding what that hex
means is a hole 'nother level of hurt.

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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