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timers
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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