[time-nuts] NTP on RaspberryPi

Chris Albertson albertson.chris at gmail.com
Sun May 26 12:30:47 EDT 2013


NTP does not really "sync" to a server.  What it does is "use the set
of reference clocks that pas the clock selection criteria".  THere is
an algorithm that determines if a reference clock is reasonable or
not.    A reference clock can be a GPS or another NTP server or a cell
phone service or any of a dozen other things but GPS and other servers
are by far the most common.

Your RPI is three leves removed from a GPS.  It is operating as
"stratum 3" the second RPI is stratum 2.  Both are doing really good
for using a networked ref. clock.   I would not blain the RPI.  If you
are doing better than a millisecond with no local PPS it is good.

On Sun, May 26, 2013 at 9:15 AM, folkert <folkert at vanheusden.com> wrote:
>> > Besides I got them to run NTP and they're too jittery for my taste.
>>
>> How good/bad were they?
>> What were you using for a time source?  Does it have PPS support?
>
> Here's ntpq -c pv for one of my RPIs after 25 days of uptime:
>
> associd=0 status=0615 leap_none, sync_ntp, 1 event, clock_sync,
> version="ntpd 4.2.6p5 at 1.2349-o Fri May 18 20:30:57 UTC 2012 (1)",
> processor="armv6l", system="Linux/3.8.10+", leap=00, stratum=3,
> precision=-20, rootdelay=25.184, rootdisp=73.646, refid=83.98.201.134,
> reftime=d54cac1f.18aa9126  Sun, May 26 2013 17:43:27.096,
> clock=d54cb273.b755933f  Sun, May 26 2013 18:10:27.716, peer=34195,
> tc=10, mintc=3, offset=0.182, frequency=-47.006, sys_jitter=0.377,
> clk_jitter=0.558, clk_wander=0.051
>
> Hmmm found out that it syncs to random hosts on the internet.
>
> Ok an other one which syncs against an other pc with PPS (and a few
> others):
>
> folkert at weerpi ~ $ ntpq -c rv
> associd=0 status=0615 leap_none, sync_ntp, 1 event, clock_sync,
> version="ntpd 4.2.6p5 at 1.2349-o Fri May 18 20:30:57 UTC 2012 (1)",
> processor="armv6l", system="Linux/3.8.10+", leap=00, stratum=2,
> precision=-20, rootdelay=0.807, rootdisp=7.669, refid=192.168.64.100,
> reftime=d54cb1e1.9d6e8f07  Sun, May 26 2013 18:08:01.614,
> clock=d54cb2e4.7d1cdae3  Sun, May 26 2013 18:12:20.488, peer=41936, tc=9,
> mintc=3, offset=0.220, frequency=-31.405, sys_jitter=0.647,
> clk_jitter=0.074, clk_wander=0.003
>
> folkert at weerpi ~ $ uptime
>  18:12:25 up 15 days,  3:48,  1 user,  load average: 0.12, 0.17, 0.15
>
>
> Folkert van Heusden
>
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-- 

Chris Albertson
Redondo Beach, California


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