Re: [chrony-users] Chrony configuration with GPS+direct PHC

["Kevin P. Fleming" <kevin@xxxxxxx>]

On Tue, May 25, 2021 at 7:00 AM Kevin P. Fleming <kevin@xxxxxxx> wrote:
>
> On Tue, May 25, 2021 at 6:47 AM Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:
> >
> > On Tue, May 25, 2021 at 06:37:31AM -0400, Kevin P. Fleming wrote:
> > > Unfortunately that was not successful; Chrony locks onto the PPS
> > > refclock for a few seconds, then changes to an external server and
> > > marks the PPS refclock as 'x'. Should I add a 'lock' directive to the
> > > PPS refclock to force it to be combined with the GPS refclock?
> > >
> > > If it's useful, I've posted a refclocks log at
> > > https://km6g.us/1-refclocks-log.txt.
> >
> > It looks like the GPS is still generating a PPS signal with 100ms
> > width. Maybe that setting to 500ms was not saved to EEPROM and it was
> > reset back after power cycle?
> >
> > Enabling the lock option would be recommended, but that is not related
> > to the PPS width problem.

Just to close out this thread: my initial attempt to configure the
timepulse (from a u-Blox M8N) was not successful, but the second
attempt was. The PPS refclock now shows up only once per second in the
reflocks log.

With that change made, and this configuration in chrony.conf:

refclock SHM 0 refid GPS precision 1e-1 offset 0.055 noselect
refclock PHC /dev/ptp3:extpps:nocrossts refid PPS width 0.5 lock GPS
precision 1e-7
pool us.pool.ntp.org iburst

I have these results:

root@edge21-b:~# chronyc sources
MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
#? GPS                           0   4   377    15    +38ms[  +38ms] +/-  100ms
#* PPS                           0   4   377    14    -15ns[  -45ns] +/- 1227ns
^- clock.fmt.he.net              1  10   377   568   -597us[ -588us] +/-   36ms
^- t2.time.gq1.yahoo.com         2  10   377   653   -718us[ -705us] +/-   37ms
^- 45.15.168.198                 2  10   373   678   +795us[ +809us] +/-   52ms
^- tick.srs1.ntfo.org            3  10   377   443  -1316us[-1312us] +/-  212ms

root@edge21-b:~# chronyc sourcestats
Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev
==============================================================================
GPS                        10   8   144   -129.155    142.247    +29ms  4121us
PPS                         6   3    81     -0.000      0.002     -1ns    12ns
clock.fmt.he.net           29  15  378m     +1.124      0.081   +178us   811us
t2.time.gq1.yahoo.com      17  11  275m     +1.111      0.182  +1929us   914us
45.15.168.198               9   4  154m     +0.994      0.288  +3233us   468us
tick.srs1.ntfo.org          6   3   86m     +1.319      3.044  +1241us  1371us

The SHM refclock shows a variable offset on top of the 55ms that I've
included in the configuration, but it's well within the 200ms
threshold for locking to the PPS refclock.

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