David J Taylor wrote:
Hello All,
I've (temporarily) given up on the idea of using Linux for the OS, and
moved to FreeBSD, with the same GPS hardware, using some of the
information on this web page:
http://www.satsignal.eu/ntp/FreeBSD-GPS-PPS.htm
ntpq -p now says:
remote refid st t when poll reach delay offset
jitter
==============================================================================
*dns1.rmplc.co.u 195.66.241.3 2 u 25 64 1 6.889 1.226
0.615
91.220.127.250 130.88.200.6 3 u 24 64 1 5.600 4.940
0.274
GPS_NMEA(1) .PPS. 0 l 39 64 1 0.000 0.826
0.001
So, I *think* that everything is okay, and it is using the PPS signal.
There is one slight worry, which is what I see in /var/log/messages:
Feb 2 09:50:16 tock ntpd[1573]: refclock_nmea: time_pps_kcbind
failed: Operation not supported
Please note, I have not done any recompiling of the kernel at this
stage - just using the GENERIC kernel, because after reading the
comments from Per Hederland in the System software customisation
section of the above web page, it seemed unnecessary. Comments?
Thanks for your help!
Paul.
Paul,
I know little about FreeBSD, so I don't know what the error message
means. I would wait a little while, and if the "reach" for the
GPS_NMEA(1) reaches 377, I reckon you're OK. On the Intel Atom system
here, it shows offset: 0.002 and jitter: 0.004 (these are in milliseconds).
I would have expected the poll for the GPS/PPS driver to be 16, and not
64. Here's an extract of what I have in the ntp.conf:
________________________________
server 127.127.20.1 mode 0 minpoll 4 maxpoll 4 prefer
fudge 127.127.20.1 flag1 1 flag3 1 refid PPS
server 0.uk.pool.ntp.org iburst minpoll 10 maxpoll 10
server 1.uk.pool.ntp.org iburst minpoll 10 maxpoll 10
server 2.uk.pool.ntp.org iburst minpoll 10 maxpoll 10
________________________________
Forcing the Internet servers to be 1024s polling always. I don't have
any note that I needed to recompile the kernel, so perhaps it was an
install option.
If you find any errors on the Web page, or there is something you would
like explained better, or to add, please tell me. I'm glad you found it
helpful - well, some of it!
On NetBSD-5 with ntpd 4.2.6p5 the default is 64s.
I've just added the "minpoll 4 maxpoll 4" back to my ntp.conf
as it could reduce the 30 usec offset blips I get when logs are
rotated.
On my two pool servers I have named internet servers with
"minpoll 8 maxpoll 10 iburst" which gives reasonably fast
recovery from internet outages.
Temperature changes here mean that on pcs that don't have
a PPS source "minpoll 10" just doesn't work and leads to
ntpd stepping the clock.
David
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