Re: More on NMEA time oscillating problem

[Gary E. Miller]

Yo Steven!

On Thu, 25 Mar 2021 14:59:02 -0500
Steven Sommars <stevesommarsntp@gmail.com> wrote:

> My previous description was erroneous, so I'll explain my observations
> again.

What o you think you got wonrg last time?

> Uputronics board with Ublox MAX-M8Q.
> identifies as PROTVER=18.00

Good.

> Baud rate = 9600, except where stated.

Bad.

> Host = RPi4.   (GPIO)
> gpsd version varies.   Started directly by root.
>            gpsd [-b] -n /dev/ttyS0 /dev/pps0              # -b used
> for NMEA only tests
> chrony 3.4
> 
> refclock SHM 0 delay 0.5 refid NMEA
> refclock SHM 2 offset 0.0  refid PPS

Can you verify no MAGIC_HAT option?

> Plus two local servers with "noselect"

Bad, no quorum.

> I've used gpsd with default configurations for years, no ubxtool.

Note the gpsd default changes regularly.

> During unrelated debugging, I ran gpsd from git head on March 9, 2021.
> The serial arrival time oscillated.  See plot in offset1.jpg.

Looks "normal".

> In addition to the oscillation, chrony was often in alarm.

I would expect that as no quorum.

> The oscillation was gpsd version dependent: 3.21 was fine.  3.22 (and
> git head) was not.

I depends on a lot more than gpsd version.

> No manual ublox configuration was done during this time.

But did you reset to factory first?

>  gpsd was
> doing its thing, of course.
> I also rebooted and power cycled the Rpi; no change.
> 
> Next, I enter the domain of ubxtool by varying the serial line rate.
> 4800 baud was too slow.
> 9600 and up worked fine for gpsd 3.21

Not really.  And as 3.21 eneables different messages, 9600 is even worse.

>   gpsd 3.22 was more
> interesting, see plot offset2.gif

Nothing interesting, exactly as you should expect.

> At 9600 / 19200 baud chrony was in alarm about half the time.  At
> 38,400 baud or higher the alarms went away.

Of course that also means you PPS is broken.

> 3.22 (and git head) were fine when gpsd was started with the "-b"
> option.

For some definition of "fine".  You disabled data that others want
enabled.

> I'm reporting this as an oddity; simple workarounds exist.

Nothing odd.  Exactly as previously discussed here.

> If this is pilot error, I'd like to correct my procedures.

The plots are exactly as I would expect.

> If this is a ublox config problem, I could get a new board.

Nope, as expected.

>  [I have
> already tried ubxtool -p RESET]

Shoulda mentione that first.

All you have proven, again, is that your PPS is not working, your baud
rate is too slow and your chronyd config has no quorum.

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

pgpYbsMzo_4VB.pgp
Description: OpenPGP digital signature