[ntp:questions] Support for "tickless" systems

David Taylor david-taylor at blueyonder.co.uk.invalid
Thu Nov 20 14:43:16 UTC 2014


On 20/11/2014 11:02, Miroslav Lichvar wrote:
[]
> It seems it's not running in the tickless mode and the problem with
> zero jitter is caused by something else.
>
> Do you have PPS kernel discipline enabled in your ntpd config (flag3)
> and which driver do you use? The PPS discipline is always disabled
> when the Linux kernel is compiled with NO_HZ, so I think that could
> explain what you are seeing. I'm not sure if that would be an ntpd bug
> or kernel bug, but I can look into it.

OK, well, this is a start if that's not tickless.  The relevant parts of 
the NTP configuration are:

server 127.127.22.0 minpoll 4 maxpoll 4
fudge 127.127.22.0  flag3 1  refid KPPS

server 127.127.28.0 minpoll 4 maxpoll 4
fudge 127.127.28.0 time1 0.138 refid GPSD

This is using the latest Raspberry Pi Linux kernel which has PPS support 
for the GPIO pins, ans this is confirmed working with the ppstest command:

pi at raspberrypi ~ $ sudo ppstest /dev/pps0
trying PPS source "/dev/pps0"
found PPS source "/dev/pps0"
ok, found 1 source(s), now start fetching data...
source 0 - assert 1416494463.000002094, sequence: 67962 - clear 
0.000000000, sequence: 0
source 0 - assert 1416494464.000002311, sequence: 67963 - clear 
0.000000000, sequence: 0
source 0 - assert 1416494465.000007529, sequence: 67964 - clear 
0.000000000, sequence: 0
source 0 - assert 1416494466.000002747, sequence: 67965 - clear 
0.000000000, sequence: 0
^Cpi at raspberrypi ~ $

Thanks for your comments on the bug report.

-- 
Cheers,
David
Web: http://www.satsignal.eu



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