[ntp:questions] ntpd: time reset problem
David Lord
snews at lordynet.org
Sat Sep 26 11:07:13 UTC 2009
David Lord wrote:
> Below are values for offset and jitter from polls at
> 30 min intervals.
>
> BR-304 gps18x-lvc gps18x-lvc
> rmc rmc rmc+pps
> polls offset polls offset polls offset
> % n (ms) % n (ms) % n (ms)
> 50 90 9.23 51 27 0.07 54 76 0.002
> 95 170 53.02 92 49 0.16 99 140 0.005
> 99.5 178 435.84 100 53 0.20 100 141 0.006
>
> Problem with BR-304 was lack of sensitivity and being
> unable to keep sufficient satellites in view, even
> though positioned with slightly better view of sky than
> the Garmin.
Oops again since I'd deleted jitter results as I'd missed sorting
them separate from the offsets. I'll put up a link to full table
of results, once I've finished trying various sources and also
settled on a reasonably consistent method for showing results.
These can even include those from when using chrony with
demand dial.
Anyway here are what I have so far:
Source Polls % offset jitter % offset jitter % offset jitter
@30min (ms) (ms) (ms) (ms) (ms) (ms)
(1) 141 54 0.002 99 0.005 100 0.006
(2) 100 51 0.07 92 0.16 100 0.20
(3) 179 50 9.23 95 53.02 99.5 435.8
(4) 203 50 0.185 0.086 95 0.642 0.255 99.5 1.111 0.488
(5) 53 50 0.165 0.070 95 0.621 0.246 99.5 0.673 0.333
(6) 164 50 1.928 95 9.162 99 21.48
(7) 174 50 0.847 95 2.548 99 6.548
VIA EPIA C3-600
NetBSD 4.1/4.99x/5.0 then 5.0.1
(1) GPS_NMEA gps18x-lvc + rmc + pps
(2) GPS_NMEA gps18x-lvc + rmc
(3) GPS_NMEA gs-br-304 + rmc
(4) SHM MSF + serial + "radioclkd2 -s timepps tty00:-dcd"
(5) SHM + PPS MSF + serial + "radioclkd2 -s poll tty00:-dsr"
(6) PARSE DCF77 + serial
(7) SHM DCF77 + serial + radioclkd2 + SHM
(not sure if using timepps kernel)
I didn't need serial-usb until very recently as all pcs here
except new netbook have serial port so a converter wasn't
needed when I tried out the GPS modules. I can't get converters
to work reliably from ttl out of either Conrad module or my
PPS extractor monostable both used for (5) above. I suspect a
ttl to rs232 conversion is needed or some simple hack.
David
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