[ntp:questions] Re: NMEA refclock - PPS not working

R Jenkins not at pub.lished
Tue May 16 14:45:47 UTC 2006


"Hal Murray" <hmurray at suespammers.org> wrote in message 
news:LKCdnX6Y4-cq_vTZnZ2dnUVZ_sSdnZ2d at megapath.net...
>
>>I have an nForce 4 board here, and it has a "spread specturm" option in
>>the BIOS. I believe this option "fuzzes" the processor clock by a few
>>percent in either direction, in order to avoid outputting lots of RF
>>noise on a single frequency. This option was on by defualt on my board.
>>You might want to make sure it is disabled, as it could certainly cause
>>ntpd to do Bad Things.
>
> It's a common trick in modern PCs.  I doubt if it causes any troubles.
>
> Note that the clock only gets stretched.  If you shrink it you violate
> timings.  It's pretty easy to measure.  Just compare the cycle counter
> with the clock and notice that your clock is running a bit slower than
> expected.
>
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Hi,

thanks for the tip, this was something I checked early on when setting up 
NTP on that machine.

As you say, BIOSs often seem to have Spread Spectrum enabled by default.

Robert Jenkins.





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