[time-nuts] ***SPAM*** Oncore m12+t PPS sawtooth correction board.

Poul-Henning Kamp phk at phk.freebsd.dk
Wed Dec 3 01:49:54 EST 2014


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In message <DECE7BA6-65E7-4C1E-A424-7E258A020E84 at sfr.fr>, Mike Cook writes:

>> I'm using a soekris net4501 that I hacked according to
>> http://www.febo.com/time-freq/ntp/soekris/

>> Recenlty I felt the need to add hardware sawtooth correction.

For the net4501 that is probably a bad idea.

When you do the sawtooth correction in software, the hw-component
acts as a jitter to smooth out the net4501's ~120nsec timestamping
window.

Without this jitter, you will have the timestamps sit in the same
window for long periods of a time and then suddenly switch to to
the neighboring window rather rapidly.

With the jitter the switch gets "smeared" out over a longer
period of time, which is a more sensible input to a PLL.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.



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