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

Tom Wimmenhove tom.wimmenhove at gmail.com
Wed Dec 3 09:03:03 EST 2014


Poul,

This is a good point and I hadn't thought of that. I'll make sure the pin
header going over to the soekris board will still receive the 'dirty' PPS
signal, and route the corrected signal only to the SMA connector on the
board.

On Wed, Dec 3, 2014 at 1:49 AM, Poul-Henning Kamp <phk at phk.freebsd.dk>
wrote:

> --------
> 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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