Re: NMEA but no PPS in ntp, Ubuntu 18.04.5

[Gary E. Miller]

Yo Steve!

On Tue, 1 Dec 2020 11:54:04 -0600
Steve Bourland <sbourland@swri.org> wrote:

> > Yes, get a fix first.  You can use cgps to know when ou have a fix.
> So from cgps on the server today:

Only 5 sats used, and they have marginal SNR.  On the ragged edge of a 3D
fix.

> (Sorry, I did some whitespace editing in hopes that comes through
> well on the other end)

Good enough.  Adding as text attachment avoids most email issues.

> So that looks to me like I have a fix or am I reading it incorrectly?

Yes, 3D fix with DGPS.  So gpsd should be sending PPS.

> % ntpq -pn
>       remote           refid      st t when poll reach   delay
> offset jitter
> ===============================================================================
> xSHM(0)     .NMEA.        0 l    -   16  377   0.0000 -173.812 23.2042
>  SHM(1)     .PPS.         0 l    -   16    0   0.0000

But no PPS.  You also do not have enough other chimers.  Hard to
vote with only 2 voters.

> # ppstest /dev/pps0
> trying PPS source "/dev/pps0"
> found PPS source "/dev/pps0"
> ok, found 1 source(s), now start fetching data...
> source 0 - assert 1606844580.999843801, sequence: 87291 - clear 
> 1606844581.099837210, sequence: 87291

That is good.  What is your gpsd command line?  See it this way:
        # pstree -paul | fgrep gpsd

> So is this a case where gpsd is feeding the kernel pps but not ntp's 
> shared memory?

Uh, you have if backwards.  The kernel feeds PPS to gpsd.  Then gpsd
uses a SHM to eed it to ntpd.

> The shared memory looks "correct" to me as best I can  tell:

Yeah, but what is in the SHM?

What does ntpshmmon show you?  Somthing like this:

# ntpshmmon
ntpshmmon: version 3.21.1~dev
#      Name  Seen@                 Clock                 Real                 L 
Prc
sam NTP0 1606845882.050103448 1606845881.573978673 1606845867.999628191 0 -20
sam NTP1 1606845882.050114664 1606845881.462974487 1606845881.462907608 0 -30
sam NTP1 1606845882.463990992 1606845882.463088891 1606845882.463021608 0 -30

> Although with the perms at 600 for segments 1 and 2, could that be
> the issue?

You need to be running gpsd and ntpd as root, of course.

> I would think if that were the case the NMEA would have
> the same problem?

Yes.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        gem@rellim.com  Tel:+1 541 382 8588

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    "If you can't measure it, you can't improve it." - Lord Kelvin

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