Re: GPSD Not Using /dev/pps0 But ppstest Shows /dev/pps0 is OK

[Joshua Quesenberry]

I just tried ntpshmmon again, this time while the command you recommended for creating the log and it IS outputting information now. Narrowing it down, it looks like `-n` is making the difference here. My application is also now seeing gps_data_t's toff and pps being populated. So now that I have the data coming through, I have a few questions about what I'm seeing.

1606955292 INFO  GPS: Sys Time: 1606955292265
1606955292 INFO  GPS: GPS Time: 1606955290.900000
1606955292 INFO  GPS: toff.real  - tv_sec: 1606955291, tv_nsec: 0
1606955292 INFO  GPS: toff.clock - tv_sec: 1606955291, tv_nsec: 593536920
1606955292 INFO  GPS: pps.real   - tv_sec: 1606955291, tv_nsec: 0
1606955292 INFO  GPS: pps.clock  - tv_sec: 1606955291, tv_nsec: 593536920

1606955292 INFO  GPS: Sys Time: 1606955292271
1606955292 INFO  GPS: GPS Time: 1606955291.000000
1606955292 INFO  GPS: toff.real  - tv_sec: 1606955291, tv_nsec: 0
1606955292 INFO  GPS: toff.clock - tv_sec: 1606955291, tv_nsec: 593536920
1606955292 INFO  GPS: pps.real   - tv_sec: 1606955291, tv_nsec: 0
1606955292 INFO  GPS: pps.clock  - tv_sec: 1606955291, tv_nsec: 593536920

What is the difference between toff and pps?

Should toff be equal to the time in gps_fix_t's time variable?

What is the difference between real and clock?

It looks like all four are aligned more with the GPS time than the System time, I was expecting them to be relating to the System time since the PPS timestamp comes from the Kernel? Is there some conversion happening to base them off GPS instead of System timestamp?

The tv_nsec portion of each isn't changing that often, I'm not sure what that means, seems like it should be incrementing by 100,000,000 each update since I have my GPS running at 10Hz?

On Wed, Dec 2, 2020 at 7:41 PM Gary E. Miller <gem@rellim.com> wrote:

Yo Joshua!

> On Wed, 2 Dec 2020 18:42:09 -0500
> Joshua Quesenberry <engnfrc@gmail.com> wrote:
>
> > I see similar sets of those PPS lines all throughout the file, last
> > set at lines 49185 - 49190. 
>
> My mistake.  Not sure what I did wrong, but there they are.
>
> The "accepted" means that SHM(2) should have gotten the PPS time.
> And yet you do not see it with ntpshmmon?  Very odd.
>
> This says that pps is on SHM(0):
>
> gpsd:INFO: PPS:/dev/pps0 ntpshm_link_activate: 0

Uh, oh.  I read that wrong.  0 means it is NOT activated.  I'll got look
at the code, and make the message more clear.

    GPSD_LOG(LOG_INF, &context.errout,
             "PPS:%s ntpshm_link_activate: %d\n",
             device->gpsdata.dev.path,
             device->shm_clock != NULL);

RGDS
GARY
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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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