| Re: [chrony-users] Setting up Chrony with PPS |
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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 | unruh@xxxxxxxxxxxxxx
Canada V6T 1Z1 | and Gravity | www.theory.physics.ubc.ca/
On Sun, 21 Feb 2016, Deven Hickingbotham wrote:
I believe the stats that appear below with show that the system problem was
just poor antenna placement.
On 2/19/2016 7:46 AM, Miroslav Lichvar wrote:
When chronyd has some NTP sources, you may want to tweak the offset
value of the SHM refclock so the measured offset as reported in
"chronyc sourcestats" is close to zero and the PPS signal can be
locked to it properly.
Given the figures below, how should offset and delay be calculated?
Finally, any other suggestions for how to setup chrony.conf to quickly
converge to PPS time after startup or acquisition of GPS signal?
chrony.conf:
server 0.us.pool.ntp.org
server 1.us.pool.ntp.org
server 2.us.pool.ntp.org
server 3.us.pool.ntp.org
refclock PPS /dev/pps0 lock NMEA refid PPS
refclock SHM 0 offset 0.5 delay 0.2 refid NMEA noselect
You just copied those out of the chrony docs.
Your offset is -140ms, and you had 500ms offset, so make it 360.
Now your nmea offset fluctuates a lot, but it does not really matter since
it's time is used only to the nearest second anyway.
210 Number of sources = 6
MS Name/IP address Stratum Poll Reach LastRx Last sample
========================================================================
#* PPS 0 4 377 19 -24ns[ -194ns] +/-217ns
#? NMEA 0 4 377 17 -148ms[ -148ms] +/-102ms
^- services.quadranet.com 3 10 377 41 -2088us[-2088us] +/- 62ms
^- time-c.nist.gov 1 10 237 224 -37ms[ -37ms] +/- 80ms
^- clock.xmission.com 1 10 377 81 -8631us[-8631us] +/- 25ms
^- leeloo.scurvynet.com 2 10 377 662 -3173us[-3141us] +/- 89ms
OK, that looks much better. the fluction in the PPS is now ns, not ms.
(I certainly would not believe the time the ns accuracy, but it is probably
good to microseconds).
I am surprized that you have ms fluctuations in the network clocks. Again, it
looks like your network uses smoke signals, rather than wires/wireless, or
your network is really overused.
Your freq and frq skew for nmea below seem really large to me, but I must say
I have not run nmea for a long time.
Anyway, I would say that you are set up.
Look at the assert and clear flags in /sys to see if they are now stable.
210 Number of sources = 6
Name/IP Address NP NR Span Frequency Freq Skew Offset Std Dev
========================================================================
PPS 7 5 96 -0.002 0.011 -24ns 128ns
NMEA 8 7 113 +226.686 403.511 -148ms 5486us
services.quadranet.com 6 3 85m +0.913 1.222 -1893us 635us
time-c.nist.gov 10 8 241m +0.946 0.273 -36ms 955us
clock.xmission.com 17 9 275m +0.881 0.219 -8139us 1216us
leeloo.scurvynet.com 40 21 530m +1.072 0.228 -120us 4307us
Reference ID : 80.80.83.0 (PPS)
Stratum : 1
Ref time (UTC) : Sun Feb 21 15:10:09 2016
System time : 0.000000000 seconds fast of NTP time
Last offset : -0.000000242 seconds
RMS offset : 0.000015393 seconds
Frequency : 3.375 ppm fast
Residual freq : -0.002 ppm
Skew : 0.016 ppm
Root delay : 0.000000 seconds
Root dispersion : 0.000020 seconds
Update interval : 16.0 seconds
Leap status : Normal
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