[ntp:questions] LAPIC timer and PIT

Jason Rabel jason at extremeoverclocking.com
Tue Sep 4 14:29:48 UTC 2007


> Spoon wrote:
> 
> > On a typical x86 motherboard, are the PIT (Programmable Interval Timer) 
> > and LAPIC (Local Advanced Programmable Interrupt Controller) timer 
> > driven by the same crystal?
> > 
> > In other words, will ntpd compute a similar frequency offset if I switch

> > from PIT to LAPIC timer?
> > 
> > Is the LAPIC timer in any way "better" than the PIT (resolution? 
> > precision? accuracy? overhead? anything else?)
> 
> Would someone care to comment?
> 
> Also, I'd be happy with links or pointers :-)

You have only one (or *maybe* two) crystal(s) on your MB. A PLL chip takes
that and generates all the various frequencies necessary for the components
to operate on the board. Stability & quality all falls back on that (cheap)
crystal. It doesn't matter how good the timer is if your timebase is no
bueno.

IIRC there is documentation on enabling / disabling APIC in the NTP Wiki.

As the name implies, APIC is a controller, not a timer. Don't get the two
confused.




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