| Re: [chrony-users] Improving local clock error |
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On Tue, 11 Dec 2018, STR . wrote:
Hi,
I see a constant ~15 ppm error in my local clock graphs using an
Uputronics uBlox MAX-M8Q GPS.
chrony-graph - https://imgur.com/a/efCFh2k
What do you mean by "local clock"? How do you know you
have a -15ppm error (ie what are you measuring?)
What are those graphs and where did you get the data? How did you get the
data?
If chrony is working at all, then the difference in rate between the system
clock and the GPS should flutuate around zero, with flucuations of perhaps
..1PPS. If you mean the real time clock, then chrony does not discipline that
There is no way to adjust its frequency.
In the tracking log, I think that the frequency offset is the comparison of
the rate of the system clock to utc if chrony were not correcting it. If the
local clock were really out by 15PPM then in a day the local clock would be
out many seconds.
How do I improve this, set 'maxclockerror' to 10 or 13 ppm?
No . Buy a new computer.
root@apu:~# chronyd -v
chronyd (chrony) version 3.4 (+CMDMON +NTP +REFCLOCK +RTC +PRIVDROP
-SCFILTER -SIGND +ASYNCDNS -SECHASH +IPV6 -DEBUG)
root@apu:~# uname -a
Linux apu 4.14.82 #0 SMP Tue Dec 4 11:28:56 2018 x86_64 GNU/Linux
chrony.conf - https://paste.ubuntu.com/p/8xvM7zzjGN/
chronyc log - https://paste.ubuntu.com/p/4SYks6ZR4S/
What are PHC{3,4}? Are the two PPS really independent or are they the same
gps source? Do their interrupts collide?
What else could I do to improve clock performance? It is looking good. It is
keeping time to microseconds, which you really cannot do much better than
that.
Cheers,
S
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