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Groups > comp.os.ms-windows.programmer.nt.kernel-mode > #18

Re: timers

Cross-posted to 4 groups.

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> BTW, I think ACPI offers an additional timer that could be used
> for this purpose.At least Windows seems to go this route in it's
> implemenation of the DosTmrXXX equivalents.

It's not ACPI.  It's the hardware.  There are three major "timer" 
interrupt sources in a modern PC machine: channel #0 of the Programmable 
Interval Timer which is nowadays integral to the PCI-to-ISA or 
PCI-to-LPC bridge chip, the High Precision Event Timer on the 
host-to-PCI bridge chip, and the timers built in to each local APIC. 
There are additional sources of *counters*, such as the so-called "PM 
timer" and the TSC processor register, which don't generate timer 
interrupts.

Which is used when is not simple.  It's not possible to say "Windows 
uses X", because that varies from HAL to HAL and according to how 
Windows happens to have been bootstrapped on each particular occasion. 
KeQueryPerformanceCounter() calls HAL functions, and the 
USEPMTIMER/USEPLATFORMCLOCK and (old) USE8254 options, passed to the 
Windows boot loader and settable on boot manager entries, control how 
several of those HAL functions (varying by HAL, of course) behave.

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Re: timers Jonathan de Boyne Pollard <J.deBoynePollard-newsgroups@NTLWorld.COM> - 2011-08-09 13:21 +0100

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