[ntp:questions] Re: Question to NTP developers

David L. Mills mills at udel.edu
Fri Aug 25 16:32:41 UTC 2006


Eugen,

You don't need a level converter. Compile the kernel with

options	PPS_SYNC
device	pps

and connect the PPS signal to the parallel port ACK pin (I forget which 
pin). Configure MINPOLL and MAXPOLL for 4. Use the fudge time1 option to 
wiggle the serial timecode offset close to the PPS offset. I do that 
here with two servers and find them within 30 microseconds of true tick.

The ATOM driver is useful to reduce residual jitter and as a means for 
fudge.

Dave

Eugen COCA wrote:
> David L. Mills wrote:
> 
>>Eugen,
>>
>>Are you using the PPS driver (22)?
> 
> 
> Dave,
> 
> No, I have FreeBSD and I use PPS to discipline the kernel.
> 
> I made in this morning a change, and I use now the 22 driver and see is
> there are any differences form the previous situation. I must think to
> use a MAX232 and an inverter to generate true RS232 levels (as the
> inverter will add some delay and, I'm sure, a small portion of jitter
> due to it's own 5V supply and MAX232 internal +/- 10V inverters).
> 
> I made a temperature stabilization of one of the servers mainboard
> crystal, and the results are quite encouraging. After all, I'm decided
> to buy this year a Rb box, to see if there are any changes !
> 




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