[ntp:hackers] Comments invited

Poul-Henning Kamp phk at phk.freebsd.dk
Sun Dec 28 10:33:07 PST 2003


In message <3FEF1A4C.6BC3CD86 at udel.edu>, "David L. Mills" writes:

>During a leap second when
>the clock is for all purposes frozen, an idiot in a reading loop could
>torque the clock 2.5 microseconds into the first second after the leap.
>Not Earth shaking for sure, but maybe Earth wiggling.

I pointed the deficiencies of that aproach out to you a long time ago.

That is why FreeBSD does not guarantee timestamps to be increasing,
only to not decrease.

>I don't know if there are others than you with ambitious oscillators; we
>ran those here for some years and I got tired of upgrading the interface
>every time a new bus spec came along. First the PDP11 U bus, then the
>LSI-11 Q bus, then the SPARC S bus, then the PSA bus, then the PCI bus,
>then...

If you have a student with a soldering iron to spare, the soekris
net4501 (www.soekris.com) is an eminent and cheap hardware platform
for timestamping (http://phk.freebsd.dk/soekris-pps)  Just remove
the stock xtal and feed it a 30-40MHz frequency from an atomic driven
PLL chip.


-- 
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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