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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 16:13:57 -0500

On Tue, May 26, 2020 at 3:14 PM Gary E. Miller <address@hidden> wrote:
Much better.  Now the STATUS and CONFIG replies are there.

Next time "-v 2" makes it esier to read.

Notice this:

    version 0 nPorts 5 txErrors x0 reserved1 0
    protIds 0x0/1/5/ff (UBX/NMEA/RTCM3/None)
      Port: 0x100 (UART1)
       txPending 0 txBytes 73334073 txUsage 2 txPeakUsage 99

Overloaded tx buffer.

You also appear to be using ports 0x200, 0x300, 0x101 and 0x201?
What for?  How?

Hi Gary,

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.

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.)  I also have Windows 10 in a virtual box so I can run u-center and talk to the receiver that way.

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.

*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, 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.

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.

How did you enable the subframes?  And I do not mean UBX-RXM-SFRBX subframes.

I apologize, I don't think I understand this question.  The ublox_ZED-F9P interface document has 8 instances of "subframe".  Several of them reference getting satellite health info from the subframe, and the remaining instances all refer to the RXM-SFRBX message.  If I was going to take a wild guess at answering your question, we purchased this specific model gps because it has the capability of outputting the subframe messages.  Normally we run on commodity ublox8 recievers (like from mrobotics or hobbyking) and those do not have the capability to output these low level messages.  I am probably missing the intent of your question entirely?  Sorry?

You can see all your output messages enabled this way:

$ ubxtool -g CFG-MSGOUT,0,0,1200  -P 27.10

Wow, that's a useful command!  I definitely need to get more familiar with ubxtool ... I wrote my own code to figure out the baud and upload configuration settings to a ublox the 'hard way' and it works for our simple (ublox6, ublox8) scenarios, but ubxtool is pretty cool all the things it can do. 

Anyway, if I completely missed on your subframe question, please help me understand what you meant?


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

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