[ntp:questions] Second attempt at GPS-18 based NTP server
user at mailinator.org
Sat Feb 4 06:15:28 UTC 2012
In article <jgg8pb$diq$1 at dont-email.me>, david-
taylor at blueyonder.co.uk.invalid says...
> > The generic BSD kernel does not enable PPS support by default. You must
> > recompile to enable PPS.
> > The page you quoted says the following in the section "System software
> > customization" (about 45% down the page in the Software section):
> > System software customisation
> > Need to add one line to the Kernel configuration:
> > options PPS_SYNC
> > and recompile the Kernel. On my 133MHz/48MB system this can take
> > several hours. Note the configuration suggestions below before you
> > recompile the kernel.
> But that was FreeBSD 5.4 and some six years ago. Note that I did not make
> the same remark about FreeBSD 8 - so whether that does or does not need
> recompiling is something I don't currently know.
I did FreeBSD 8.1 with that and it was ok, and I've done FreeBSD 9.0
Main advantage for me is kernel discipline narrows down in a few
minutes, instead of a few hours. Can get a 5-10 uS spike with
aircon/heater, but otherwise it'll drift around 0-2 uS.
Advice for those going for microsecond accuracy: Find the 14.318
crystal, and see if you can cover it in polystyrene. Takes the drift
from 10 to 2 us because air can no longer reach it, only the PCB temp,
and that has more thermal mass/slower time constant.
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