Re: GPS Mac OS challenges

[Gary E. Miller]

Yo Marc!

On Fri, 10 Dec 2021 15:42:40 -1000
Marc Rosen <marc.rosen@mac.com> wrote:

> 1. Work w Gary's help to set up gpsd and ntp on my MBP laptop - this
> seems to work although hard to verify since ntpshmmon not succeeding
> yet

A -D 4 log would confirm things similar to ntpshmmon.

> 2. Original goal - have a reliable time source for off grid usage
> where accuracy to 0.5 secs is needed

Good.

> I'm using a ham radio digital mode which requires time sync. The
> program I'm using, WSJT-X, uses the Mac system time - identical to
> what is seen in the system date-time dialog and in the menu bar clock
> - upper right

Not uncommon.

> It appears that the system dialog uses an ntp server - time.apple.com
> to source the official time.

It might just be used on startup to set the system time.  Or it may be
running all the time so you can't run your own ntpd.

> My thought was to run ntp locally and then set the system dialog to
> use 127.0.0.1 as the source 

You got that backwards.  ntpd sets the system time for you, continuously,
so you do not have to think about it.  You can not run system ntp and your
own ntpd at the same timme.

> The local ntp server is listening to the GPS NMEA feed from a USB
> connected radio - although a better GPS source could be substituted 

Huh?  I thought you had gpsd listending to the GPS NMEA feed.  Only
one daemon can use the GPS NMEA at any one time.

> Clearly there are easier ways to do this - but why not see if this
> could work

Have at it.

> 3. Next challenge seems to me to be how to test and prove it's
> working as expected 

The point of ntpd is that it talks to other ntpd to show you that
it has good time for you.

> I think some of my issues in the last couple days were that I shifted
> positions by 8000km and did not let the GPS get a fix - which took an
> awful long time , over an hour

A tad long, but not completely unreasonable for an old GPS with marginal
skyview.

> started gpsd this time just as:
> >  gpsd -n /dev/cu.usbmodem1203 -ND4   

The point of the -D 4 is to get the startup log, and send it here.

Care to share that?  The first 60 seconds?

> The reason I had the -F before was that I misunderstood or merged 2
> examples I saw The reason I have the hardcoded port

Common mistake.

> I don’t know
> how to make/use a generic gpsN port for the moment

As root:
        ln -s /dev/cu.usbmodem1203 /dev/gps0

But I never saw value in the effort.

> it just means I
> have to be aware of which physical USB-C port I plug the radio into

Always.  And it is more complicated than just what port you plug in to.

> *** after all this I see the following 
> Marcs-2020-MacBook-Pro-2:bin marc$ ntpq -p
>  remote           refid      st t when poll reach   delay offset  jitter
> ==============================================================================>
>  us.pool.ntp.org .POOL.          16 p    -   64    0    0.000   +0.000 0.001

That is broken.  The reach is zero, and that should have expanded to 4
servers.

> *SHM(0)          .GPS.            0 l   19   64  377    0.000 +0.701   9.466

You are getting "good" time from your NMEA.

> SHM(1)          .PPS.            0 l    -   64    0  0.000   +0.000   0.000

But no PPS.  I'll bet your GPS is not sending any PPS, so nothing for
your gpsd to receiver.

So macOs is not running an ntpd, and your hand made ntpd is setting
your system clock for you.  Nothing more to do, except fix your pool.

> *** when I run ntpshmmon ( as root), I get:

Same as before.  I got no ideas.  Maybe an strace would help.

> ****************************************
> output from gpsdebuginfo
> ****************************************

No need for that anymore.

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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