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[time-freq] Linux PPS and FreeBSD issues

John Ackermann N8UR jra at febo.com
Fri Dec 28 18:56:06 UTC 2007

Hi Gregg --

I'm by inclination a Linux guy, but unfortunately there is some sort of
bad juju between the kernel people and the NTP people, and as a result
getting decent PPS timekeeping out of Linux is an ongoing challenge.  I
run FreeBSD (actually, the CF-based nanoBSD version) on my Soekris
servers as that seems to be the best way to make things work.

There is a shared memory (shm) program called shmpps that can pick up a
PPS signal from a serial port and pipe it to NTP, but I've had trouble
keeping that going for long uptimes.

It's a shame that Linux seems, for reasons I don't understand, to be
unable/unwilling to have the necessary kernel stuff to avoid patches,
but it's been that way for years and I haven't seen any sign of changes...


Gregg Levine said the following on 12/27/2007 06:43 PM:
> Hello!
> I've been sorting through and reading messages on news://comp.protocols.ntp .
> It seems to be an interesting study. There is a group there (or it
> seems to me to be one.) that prefers FreeBSD exclusively. And there
> are people like myself who are concerned with the PPS inclusion into
> the Linux kernel. Accordingly there are kits available for this on the
> Kernel.org server. But only for and for The author
> of the kit is interested in updating this, but he's not clear on when
> it would be released for the later 2.6 ones.
> There is even one fellow who has NTP running on his Sun box from the
> same time period as the I486DX2, he's got it running rather nicely.
> But the big question for me is simply running Linux on hardware from
> the same time period, and naturally that's what I've been up to.
> The last I time I investigated FreeBSD was during the ramp up to
> version 4.0. I daresay I never got things to work properly then. I've
> heard some interesting complaints about building a kernel for that
> operating system, versus the others from the BSD family, and Linux.
> Would anyone care to comment?

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