✘MAX-M8Q strangeness

[Gary E. Miller]

Yo All!

New options for ubxtool: -t and -tt

The first adds a timestamp of the UNIX epoch to the output.

The second also adds a timestamp of the UTC time.

Why bother?  A MAX-M8Q was acting weird.

Here you can see the ouput of a MAX-M8Q set to 1Hz, binary only:

pi3 ~ # ubxtool -tt -v 2
[...]
1594088011.2340 Tue Jul  7 02:13:31 2020
UBX-NAV-PVT:
  iTOW 180829000 time 2020/7/7 02:13:31 valid x37
  tAcc 11 nano -292404 fixType 3 flags x3 flags2 xa
  numSV 23 lon -1213143056 lat 440688580 height 1110147
  hMSL 1131497 hAcc 1731 vAcc 3139
  velN 4 velE 2 velD -5 gSpeed 5 headMot 0
  sAcc 223 headAcc 10882764 pDOP 116 reserved1 0 19168 35
  headVeh 9034 magDec 0 magAcc 0
    valid (validDate ValidTime fullyResolved)
    fixType (3D)
    flags (gnssFixOK diffSoln)
    flags2 ()
    psmState (Not Active)
    carrSoln (None)

The UTC time of the system (NTP locked) and the PVT match to the
second.

If I enable NMEA, there is a several second delay.  Here 3 seconds:

pi3 ~ # ubxtool -tt -v 2 -e NMEA -w 20
[...]
1594088258.9893 Tue Jul  7 02:17:38 2020
UBX-NAV-PVT:
  iTOW 181073000 time 2020/7/7 02:17:35 valid x37
  tAcc 13 nano -248606 fixType 3 flags x3 flags2 xa
  numSV 21 lon -1213142489 lat 440689434 height 1100017
  hMSL 1121367 hAcc 2116 vAcc 3996
  velN 29 velE -3 velD 177 gSpeed 29 headMot 0
  sAcc 373 headAcc 11180100 pDOP 113 reserved1 0 19168 35
  headVeh 9034 magDec 0 magAcc 0
    valid (validDate ValidTime fullyResolved)
    fixType (3D)
    flags (gnssFixOK diffSoln)
    flags2 ()
    psmState (Not Active)
    carrSoln (None)

A little later it goes to 6 seconds:

pi3 ~ # ubxtool -tt -v 2
[...]
1594088407.3367 Tue Jul  7 02:20:07 2020
UBX-NAV-PVT:
  iTOW 181219000 time 2020/7/7 02:20:01 valid x37
  tAcc 11 nano -221827 fixType 3 flags x3 flags2 xa
  numSV 24 lon -1213142702 lat 440689218 height 1104094
  hMSL 1125444 hAcc 1827 vAcc 3221
  velN 4 velE -2 velD 34 gSpeed 5 headMot 0
  sAcc 322 headAcc 11355104 pDOP 109 reserved1 0 19168 35
  headVeh 9034 magDec 0 magAcc 0
    valid (validDate ValidTime fullyResolved)
    fixType (3D)
    flags (gnssFixOK diffSoln)
    flags2 ()
    psmState (Not Active)
    carrSoln (None)

The serial port speed is 9600.  Doing the same thing on a NEO-M8N
does not show the problem.  I don't think the problem is a full 
serial port buffer as the delay is in even seconds.

Yet another reason not to trust a single GNSS receiver for your time...

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        gem@rellim.com  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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