On 27/11/2012 16:24, gabs wrote:
[]
The displayed jitter in loopstats or the peer list can be different from the
actual jitter of the source. This case is the reverse: low actual jitter,
15 us displayed jitter.
root@OpenWrt:/tmp# tail /tmp/ntp/loops
56257 76888.554 -0.000000080 6.553 0.000015259 0.000053 3
56257 76896.554 -0.000000098 6.553 0.000015259 0.000052 3
56257 76904.554 -0.000000071 6.553 0.000015259 0.000051 3
56257 76912.554 -0.000000061 6.553 0.000015259 0.000049 3
56257 76920.554 -0.000000091 6.553 0.000015259 0.000049 3
56257 76928.554 -0.000000008 6.553 0.000015259 0.000046 3
56257 76936.554 -0.000000048 6.553 0.000015259 0.000043 3
56257 76944.554 -0.000000014 6.553 0.000015259 0.000041 3
56257 76952.554 0.000000039 6.553 0.000015259 0.000038 3
56257 76960.554 0.000000016 6.553 0.000015259 0.000036 3
This is normal for this platform since ntpd seems to use the precision as the
lower bound for reported jitter. The precision is low as it takes 12 us to read
the clock and convert to NTP timestamp format.
For the RPi, I have no idea but I'll be getting one before the year ends :)
Oh, that's interesting, gabs. I know that Dave Hart has done some work
in that area, so in case it helps:
System with PPS signal showing zero jitter in the loopstats:
C:\>ntpq -c rv raspi-1
associd=0 status=011d leap_none, sync_pps, 1 event, kern,
version="ntpd 4.2.7p324@1.2483 Mon Nov 19 16:03:37 UTC 2012 (1)",
processor="armv6l", system="Linux/3.2.27-pps-g965b922-dirty", leap=00,
stratum=1, precision=-19, rootdelay=0.000, rootdisp=1.180, refid=PPS,
reftime=d45f851e.54f1a9c6 Tue, Nov 27 2012 18:29:50.331,
clock=d45f852a.b6780c11 Tue, Nov 27 2012 18:30:02.712, peer=5855, tc=4,
mintc=3, offset=-0.000842, frequency=-42.566, sys_jitter=0.001907,
clk_jitter=0.000, clk_wander=0.000
System working purely off LAN sync, non-zero jitter:
C:\>ntpq -c rv raspi-2
associd=0 status=0615 leap_none, sync_ntp, 1 event, clock_sync,
version="ntpd 4.2.7p321@1.2483 Fri Nov 16 15:06:21 UTC 2012 (1)",
processor="armv6l", system="Linux/3.2.27-pps-g965b922-dirty", leap=00,
stratum=2, precision=-19, rootdelay=0.505, rootdisp=3.978,
refid=192.168.0.3,
reftime=d45f84b4.981fcb01 Tue, Nov 27 2012 18:28:04.594,
clock=d45f8537.eb89aef6 Tue, Nov 27 2012 18:30:15.920, peer=7910, tc=5,
mintc=3, offset=-0.013495, frequency=-22.812, sys_jitter=0.036904,
clk_jitter=0.024, clk_wander=0.013
--
Cheers,
David
Web: http://www.satsignal.eu
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