John Allen wrote: [] > David, > > Yes, I have checked with and without FSB Spread Spectrum with both > HALs. > My observations for the 4 combinations are: > > Motherboard: A7N8X-X (nForce2) Windows XP SP 2 > > HAL: "ACPI Uniprocessor PC" (with APIC, halaacpi.dll): > 1) FSB Spread Spectrum = 0.50% : system clock unstable, NTP did not > synchronise 2) FSB Spread Spectrum = disabled : system clock > unstable, NTP did not synchronise > HAL: "Advanced Configuration and Power Interface (ACPI) PC" (no APIC, > Halacpi.dll) 3) FSB Spread Spectrum = 0.50% : system clock stable, > NTP synchronised 4) FSB Spread Spectrum = disabled : system clock > stable, NTP synchronised > It's a bit anecdotal, but it seems that FSB Spread Spectrum may not > make a big difference. However, I'm still running (3), I'll have to > check its behaviour over a longer period. > > It should be mentioned that according to the Microsoft KB article > http://support.microsoft.com/?kbid=821893 > there is a quite fundamental difference between the two DLLs: > - Halaapic.dll: uses the Real Time Clock (RTC) to generate clock > interrupts - Halacpi.dll: uses the 8254 Programmable Interval Timer > (PIT) to > generate clock interrupts > > John
That's most interesting, John. I suppose with the spread-spectrum its effect on NTP would depend on what period the spread is over, i.e. if the spread is over microseconds but NTP measures over milliseconds, the frequency may appear stable. You might want to enable the statistics collection and use a program like Meinberg's NTP Time Server Monitor: http://www.meinberg.de/english/sw/time-server-monitor.htm to see what the stability actually is. I'm also unclear whether the FSB speed will actually have any direct effect on the clocks seen by the processor, although it will obviously affect memory retrieval speed. The information on the HALs was of interest - I have a book in which some of this stuff is written up, but not the timing stuff (IIRC). "Windows Internals", fourth edition, is a good read (if you like that sort of thing). I would also appreciate seeing this type of information in the Support Twiki (as well as searchable by Google). Cheers, David _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
