Re: [chrony-users] GPS + PPS

[Dominik Auras <wohnung.elisabethstrasse@xxxxxxxxx>]

Hi,

thanks.

Chrony selects the PPS source now, but I observe a large offset of the system time. The offset to the PPS clock is nearly zero, as expected. But the system time is offset by >2000s to the NMEA and NTP time (I won't have internet access once deployed).

To the previously mentioned configuration, I've added simply noselect to the GPS refclock.

Any other idea?

BR, Dominik

2014-10-26 2:31 GMT+02:00 Tomalak Geret'kal <tom@xxxxxxxxx>:

On 26/10/2014 00:28, Dominik Auras wrote:

Hello!

I am trying to setup chrony for my new GPS. Unfortunately, chrony won't select any source if I enable both the NMEA and PPS source. I bet that my configuration is wrong ... but it is unclear to me how to configure the PPS.

Could you maybe explain me what I do wrong, or point me to something that explains it? Thank you in advance!

Part of my chrony.conf

server ptbtime1.ptb.de iburst noselect maxpoll 6 minpoll 6
refclock SHM 0 refid GPS offset 0.546 poll 6 delay 0.9999
refclock SHM 1 delay 0.2 refid PPS lock GPS
minsamples 64
makestep 1000 -1

Output of chronyc sources:

210 Number of sources = 3
MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
#x GPS                           0   6   377    82   -21.0s[ -21.0s] +/-  503ms
#x PPS                           0   4   377    22    +16ms[  +16ms] +/-  100ms
^x ptbtime1.ptb.de               1   6   377    46   -21.0s[ -21.0s] +/-   30ms

Output of chronyc sourcestats

210 Number of sources = 3
Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev
==============================================================================
GPS                        64  21   67m     -0.646      4.511   -21.0s    11ms
PPS                        64  23  1009      3.062      0.006    +16ms  3620ns
ptbtime1.ptb.de            64  33   69m      2..952      0.191   -21.0s   498us

The PPS is the rpi_gpio_ntp program running in the background.

chrony won't have internet access once it is deployed ...

BR, Dominik

I've had this problem in the past, but could never figure out what was going on. Listers suggested that it was a chrony bug but I was never able to gather enough information to pin it down.

Marking your SHM source as "noselect" prevents chrony from getting stuck when deciding which of the two refclock sources is a better match, but doesn't prevent the "lock GPS" declaration from linking the two SHM sources together.

So:

server ptbtime1.ptb.de iburst noselect maxpoll 6 minpoll 6
refclock SHM 0 refid GPS offset 0.546 poll 6 delay 0.9999 noselect
refclock SHM 1 delay 0.2 refid PPS lock GPS
minsamples 64
makestep 1000 -1

Perhaps give that a go.

Tom