High Precision Event Timer (HPET)

This function provides a set of timers that can be used by the operating system. The timers are defined such that the operating system may assign specific timers to be used directly by specific applications. Each timer can be configured to cause a separate interrupt.

The processor provides eight timers. The timers are implemented as a single counter with a set of comparators. Each timer has its own comparator and value register. The counter increases monotonically. Each individual timer can generate an interrupt when the value in its value register matches the value in the main counter.

Timer 0 supports periodic interrupts.

The registers associated with these timers are mapped to a range in memory space (much like the I/O APIC). However, it is not implemented as a standard PCI function. The BIOS reports to the operating system the location of the register space using ACPI. The hardware can support an assignable decode space; however, BIOS sets this space prior to handing it over to the operating system. It is not expected that the operating system will move the location of these timers once it is set by BIOS.