[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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