Ah OK, I guess the part that was not clear to me was that chronyd _creates_
this socket when configured with refclock SOCK, rather than simply connecting
to it.
When I configured this and restarted chronyd and then gpsd, it did create the
socket file. However, `chronyc` does not report any updates being received from
this source.
I did not find an AppArmor profile that is currently being enforced on gpsd.
I did notice that AppArmor was preventing chronyd from creating
/run/chronyd.pps0.sock, so I corrected that and switched the configuration to:
refclock SOCK /run/chrony.ttyAMA1.sock refid GPS precision 1e-1
refclock SOCK /run/chrony.pps0.sock refid PPS precision 1e-7
However I still do not receive any updates.
Ryan
> On Sep 15, 2020, at 3:20 PM, Avamander <avaman...@gmail.com> wrote:
>
> > but also I don’t see that socket you’re referencing being created.
> > I don’t see any AppArmor logs that seem to indicate anyone was prevented
> > from creating this file.
>
> Have you actually told chrony to create it?
>
> > for a while but the PPS never updated:
>
> Yes, this is exactly why I suggested you check the AppArmor policy itself.
> When the pps device is inaccessible gpsd gives some vague error about the pps
> device and that's it. Open gpsd's log and verify it hasn't thrown an error
> about the pps device during startup.
>
> > I couldn’t readily find much documentation on SHM 0 vs SHM 1.
>
> Yes, this is awfully documented online.
>
>
>
> On Tue, Sep 15, 2020 at 10:08 PM Ryan Govostes <rgovos...@whoi.edu> wrote:
> Below Bill argued against using /var/run/chrony.ttyAMA0.sock, but also I
> don’t see that socket you’re referencing being created. I don’t see any
> AppArmor logs that seem to indicate anyone was prevented from creating this
> file. Perhaps the version is too old?
>
> I couldn’t readily find much documentation on SHM 0 vs SHM 1. I did find
> this, which suggests using SHM 1 instead of having chrony go directly to the
> PPS device, as in:
>
> refclock SHM 0 refid GPS precision 1e-1
> refclock SHM 1 refid PPS precision 1e-7
>
> https://gpsd.gitlab.io/gpsd/gpsd-time-service-howto.html#_feeding_chrony_from_gpsd
>
> I restarted chronyd with this configuration and watched `chronyc sources` for
> a while but the PPS never updated:
>
> 210 Number of sources = 2
> MS Name/IP address Stratum Poll Reach LastRx Last sample
>
> ===============================================================================
> #* GPS 0 4 377 22 +1104us[+4464us]
> +/- 100ms
> #? PPS 0 4 0 - +0ns[ +0ns]
> +/- 0ns
>
> I disabled systemd-timesyncd as you suggested, thanks.
>
> Ryan
>
> > On Sep 15, 2020, at 2:42 PM, Avamander <avaman...@gmail.com> wrote:
> >
> > First, disable systemd-timesyncd if you're using chrony: sudo systemctl
> > disable --now systemd-timesyncd
> >
> > Second, enable chrony, pretty sure it isn't enabled by default after
> > install: sudo systemctl enable chrony
> >
> > Why do you want to SHM 0 (non-PPS-corrected) NMEA time, instead of SHM 1 or
> > /var/run/chrony.ttyAMA0.sock?
> >
> > On Tue, Sep 15, 2020 at 9:36 PM Ryan Govostes <rgovos...@whoi.edu> wrote:
> > Thanks, I removed the offset and delay so the reference clock configuration
> > is now:
> >
> > refclock SHM 0 refid GPS precision 1e-1
> > refclock PPS /dev/pps0 refid PPS
> >
> > My intention is to have GPS set the system date and time and then have the
> > PPS signal keep it from drifting.
> >
> > After applying this, I ran again and am now getting:
> >
> > MS Name/IP address Stratum Poll Reach LastRx Last sample
> >
> > ===============================================================================
> > #x GPS 0 4 377 16 +587us[
> > +587us] +/- 100ms
> > #x PPS 0 4 160 82 -128ms[
> > -128ms] +/- 759ns
> >
> > The #x suggests that “time may be in error.” However I am still seeing gpsd
> > work (monitored via cgps) and the PPS device still appears to be working
> > (according to ppstest).
> >
> > Furthermore timedatectl suggests that the system clock is not synchronized:
> >
> > $ timedatectl status
> > Local time: Tue 2020-09-15 18:34:48 UTC
> > Universal time: Tue 2020-09-15 18:34:48 UTC
> > RTC time: n/a
> > Time zone: Etc/UTC (UTC, +0000)
> > System clock synchronized: no
> > systemd-timesyncd.service active: yes
> > RTC in local TZ: no
> >
> > What appears to be the problem?
> >
> > Ryan
> >
> > > On Sep 15, 2020, at 12:47 PM, Bill Unruh <un...@physics.ubc.ca> wrote:
> > >
> > >
> > >
> > > William G. Unruh __| Canadian Institute for|____ Tel: +1(604)822-3273
> > > Physics&Astronomy _|___ Advanced Research _|____ Fax: +1(604)822-5324
> > > UBC, Vancouver,BC _|_ Program in Cosmology |____ un...@physics.ubc.ca
> > > Canada V6T 1Z1 ____|____ and Gravity ______|_
> > > https://nam02.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.theory.physics.ubc.ca%2F&data=02%7C01%7Crgovostes%40whoi.edu%7C054736ed4c39434c82db08d8599714d3%7Cd44c5cc6d18c46cc8abd4fdf5b6e5944%7C0%7C0%7C637357852718387997&sdata=qHAUE4iPB4YLvLVCtFetR33HnDjEowrOa%2FpWLANdNpE%3D&reserved=0
> > >
> > > On Tue, 15 Sep 2020, Ryan Govostes wrote:
> > >
> > >> Hi all,
> > >>
> > >> I am setting up chronyd on an embedded Linux device to synchronize the
> > >> system clock using a GPS module. The GPS device sends NMEA strings over
> > >> the character device /dev/ttyAMA1 and I have also configured /dev/pps0,
> > >> both of which appear to be working OK.
> > >>
> > >> The system is running Ubuntu 18.04 and the latest package versions are
> > >> chronyd 3.2 and gpsd 3.17.
> > >>
> > >> I configured gpsd to listen to the serial device and then added these
> > >> lines to my chrony.conf:
> > >>
> > >> refclock SHM 0 refid GPS precision 1e-1 offset 0.9999 delay 0.2
> > >
> > > Why those figures for ooffset? That is 1 sec offset. NMEA is not that bad.
> > >
> > >
> > >> refclock PPS /dev/pps0 refid PPS
> > >>
> > >> When I run `chronyc sources` they both seem to be kind of working:
> > >>
> > >> 210 Number of sources = 2
> > >> MS Name/IP address Stratum Poll Reach LastRx Last sample
> > >>
> > >> ===============================================================================
> > >> #- GPS 0 4 377 12 +128ms[
> > >> +128ms] +/- 200ms
> > >> #* PPS 0 4 377 12 +6ns[
> > >> +119ns] +/- 203ns
> > >>
> > >> However it looks like the GPS source is “not combined”. Is this a
> > >> degraded state, e.g., it is using one of these two sources?
> > >
> > > Why would one want to combine GPS with PPS. PPS is good to the nanosecond
> > > level. GPS toabut 100 ms -- that is almost a million times worse. It
> > > would be like combining your wristwatch with some clock which says "its
> > > spring so it must be April".
> > >
> > >>
> > >> Also, I am not sure why the LastRx from the PPS (or frankly either)
> > >> ticks upwards so long—shouldn’t it constantly be receiving updates?
> > >
> > > Yout tell it that POLL is 4 which means 16 seconds. So every 16 seconds
> > > that
> > > clock is read. The driver massages the input ( once a second) to get rid
> > > of
> > > obvious outliers but reports to chrony once every 16 seconds. Note it is
> > > a bad
> > > idea to reduce the poll even further. Then obvious ouliers are not thrown
> > > out,
> > > and the ability to determine the rate of the clock is degraded.
> > >
> > >>
> > >> I am just using the precision / offset / delay figures that several
> > >> examples use. Is there documentation on calibrating these values?
> > >
> > > Get rid of the offset and delay. The GPS is useless except for setting
> > > actual
> > > number of the seconds.
> > >
> > >>
> > >> Finally, I read that using Unix sockets rather that shared memory is
> > >> preferable, but my chronyd does not seem to create those sockets.
> > >
> > > Why is it better? Leave things as they are. With PPS your time will be
> > > accurate to microseconds just as things are now. Do you need any better
> > > time?
> > > If you do need time to nanoseconds, then you will really have to throw
> > > away
> > > your computer (its ability to read interrupts is only at the microsecond
> > > level) and begin compensating for propagation delays in your gps unit, and
> > > also the sawtooth offset on the ns level due to your gps receiver
> > > innards. But
> > > then, why would you want to know the time to 1 billionth of a second?
> >
>
