[time-nuts] NTP, Oncore and Allan deviation
Javier Herrero
jherrero at hvsistemas.es
Wed Oct 8 10:28:28 UTC 2008
Hello all,
I'm playing around with an NTP server using a Blackfin processor and
uClinux, and a Oncore M12M-Timing. The board is our H8606,
http://www.hvsistemas.com/en/prod/H8606.html , with the standard crystal
oscillator replaced with a FOX924B TCXO,
http://www.foxonline.com/pdfs/fox924.pdf . I've modified the kernel to
support PPS from the Oncore, with timestamping done through the
processor NMI and the cycles registers, yielding a 2.5ns resolution, and
the preliminary observed jitter in the timestamping seems better than
±25ns (previous to applying Oncore sawtooth correction). So until now,
it seems quite good :).
I was thinking if the Allan intercept parameter of the ntp daemon could
be optimized for this situation, since it has a default of 1500s that I
suppose that is the adequate value for general usage (synchronization of
a rather crappy computer oscillator from a WAN with quite spaced
pollings and relatively high delays), and I presume that could be
reduced for this system. Any thoughs would be appreciated :)
Best regards,
Javier
--
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Javier Herrero EMAIL: jherrero at hvsistemas.com
HV Sistemas S.L. PHONE: +34 949 336 806
Los Charcones, 17A FAX: +34 949 336 792
19170 El Casar - Guadalajara - Spain WEB: http://www.hvsistemas.com
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