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[gpsd-dev] ✘Moving to NMEA 4.0 (extended) PRNs

From: Gary E. Miller
Subject: [gpsd-dev] ✘Moving to NMEA 4.0 (extended) PRNs
Date: Thu, 2 May 2019 19:39:42 -0700

Yo All!

I have been working on getting the ZED-F9T to work in its default NMEA
4.10 mode.  It sometimes puts NMEA 4.0 PRNs into NMEA 4.10 sentences.
Sometimes worse.

The ZED NMEA 4.10 will refer to a single satellite using multiple
different PRNs, in the same cycle.

This confused gpsd, and me.

Some people like to use both u-blox binary and NMEA sentences mixed
together, which turned into a big mess with conflicting PRNs.

Up until now, gpsd used whatever PRN the GPS said it was.  With NMEA
4.10 and u-blox 9, this is no longer sustainable.

From now on gpsd will try to convert GPS provided PRNs into NMEA 4.00
extended numbering.  Or at least start to try.  The last git push
started this change.

Why not NMEA 4.10 extended?  No one is ready for NMEA 4.10 extended
numbering which uses gnssid, svid and sigid to identify signals.

Fixing the PRNs uncovered other examples of non NMEA compliant sentences
in the regressions.  So many regressions changed.  The most obvious
change is that NMEA 4.0 extended puts the SBAS PRN in the range 33-64
and 152-158, not 120-158 as u-blox does.  Some other GPS put BeiDou
in the range 201-237 instead of the proper 401-437.

Other than the PRN numbers, nothing else changed.

If you want a qlimpse of how crays this is, look at Appendix A
of the "u-blox ZED-F9T Interface Description".  You can find it on
the u-blox site:

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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