[ntp:questions] Second attempt at GPS-18 based NTP server
snews at lordynet.org
Thu Feb 2 15:38:21 UTC 2012
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:
>> ntpq -p now says:
>> remote refid st t when poll reach delay offset
>> *dns1.rmplc.co.u 188.8.131.52 2 u 25 64 1 6.889 1.226
>> 184.108.40.206 220.127.116.11 3 u 24 64 1 5.600 4.940
>> GPS_NMEA(1) .PPS. 0 l 39 64 1 0.000 0.826
>> 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: 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!
> 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
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.
More information about the questions