Looking for ntp/PPS setup guide

[M. Warner Losh]

In message: <20040730000205.E834A5D09 at ptavv.es.net>
            "Kevin Oberman" <oberman at es.net> writes:
: > From: Gregory Bond <gnb at itga.com.au>
: > Date: Fri, 30 Jul 2004 09:38:32 +1000
: > Sender: owner-freebsd-stable at freebsd.org
: > 
: > 
: > We've got a GPS receiver to make an NTP server, and it has PPS output.
: > Is there a guide to how to set up PPS on recent (4.10-ish) FreeBSD
: > boxes?  Or I can put it on a 5.x box if that is better. I've had a
: > look in all the obvious places but the only references I can find are
: > to old (load a line discipline or patch a kernel) solutions.
: 
: I'd suggest the documentation at www.ntp.org, but it has a few errors
: and lacks a bit of FreeBSD specific bits.
: 
: First off, you will need to rebuild ntpd with the appropriate reference
: clocks, pps and whatever type of GPS you have. The software is in
: /usr/src/contrib/ntp/ntpd. You can look at the list of clock drivers and
: pick the one you need. If you look at the driver source, you will see
: that REFCLOCK and a driver specific variable need to be defined.
: 
: Go to /usr/src/usr.sbin/ntp/ntpd and rebuild ntpd with the clock driver:
: make clean
: make -DREFCLOCK -DCLOCK_yourclock
: make install
: 
: You need to rebuild you kernel with "options PPS_SYNC". You can run PPS
: without this and the man page even says it's more accurate that way, but
: my experience is that it is much more accurate with the kernel option.
: I use CDMA clocks and they my time is stable within 10 microseconds.

I've found that w/o PPS_SYNC, we get worse results than when we have
it enabled.Of course, most of my work with this is with a pps that is
from a HP5071A atomic clock :-)

: I did find that nptd 4.2 seemed to converge better than 4.1, so I built
: the ntp port instead of the standard one. I then just installed the ntpd
: from the port over the one in /usr/sbin. 4.2 is now the standard NTP in
: version 5 and I suspect it will be MFCed to STABLE soon.
: 
: Read the manual pages for pps and your GPS clock driver for how to set
: up ntp.conf for that clock. You will need to set up kernel PPS there.

This can be the hardest part.  The documentation is a little less than
stellar. :-(

Warner