[ntp:questions] Second attempt at GPS-18 based NTP server

Rhys 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.
> 
> Cheers,
> David 

I did FreeBSD 8.1 with that and it was ok, and I've done FreeBSD 9.0 
recently.

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.

Rhys.



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