[ntp:questions] drift modeling question

Martin Burnicki martin.burnicki at meinberg.de
Fri Jul 18 11:14:40 UTC 2008

David and Hal,

David Woolley wrote:
> Hal Murray wrote:
>> Most PCs have 2 xtals.  One at 14.xxx MHz (cheap, 4X color burst)
>> that drives the CPU and most motherboard logic through a magic clock
>> generator (PLL) chip, and another that is a 32 KHz watch crystal for
>> keeping time when the CPU is off.  The latter also makes interrupts
>> for the scheduler.
> Historically interrupts from the 32kHz clock have not been used, except,
> possibly, in powered down states to initiate a restart from suspend or
> hibernate.  It is possible that has changed very recently, but they
> certainly weren't used historically.

About which operating system(s) are you talking?

The PC's standard RTC chip can certainly generate cyclic interrupts.
However, if a cyclic interrupt from the RTC or from another timer chip is
used to drive the scheduler depends on the type and eventually on the
version of an operating system, isn't it? 

So one system may be using the RTC's interrupts and another one may not.

Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont

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