[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 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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