[ntp:questions] ntpd: time reset problem

Unruh unruh-spam at physics.ubc.ca
Sat Sep 26 16:32:02 UTC 2009


David Lord <snews at lordynet.org> writes:

>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

Your number 3 is really terrible. That gps should not be delivering the
time if it cannot lock on to enough sattelites. To deliver times that
are 1/2 sec out is really pretty terrible. 


>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

What is 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.

The problem is the interrupt. There is no way to deliver an interrupt to
usb AFAIK. From what I understant, seems that there is random latency in the
 usb system as well.



>David




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