| High Precision Event Timer Driver for Linux
|The High Precision Event Timer (HPET) hardware follows a specification
|by Intel and Microsoft which can be found at
|Each HPET has one fixed-rate counter (at 10+ MHz, hence "High Precision")
|and up to 32 comparators. Normally three or more comparators are provided,
|each of which can generate oneshot interrupts and at least one of which has
|additional hardware to support periodic interrupts. The comparators are
|also called "timers", which can be misleading since usually timers are
|independent of each other ... these share a counter, complicating resets.
|HPET devices can support two interrupt routing modes. In one mode, the
|comparators are additional interrupt sources with no particular system
|role. Many x86 BIOS writers don't route HPET interrupts at all, which
|prevents use of that mode. They support the other "legacy replacement"
|mode where the first two comparators block interrupts from 8254 timers
|and from the RTC.
|The driver supports detection of HPET driver allocation and initialization
|of the HPET before the driver module_init routine is called. This enables
|platform code which uses timer 0 or 1 as the main timer to intercept HPET
|initialization. An example of this initialization can be found in
|The driver provides a userspace API which resembles the API found in the
|RTC driver framework. An example user space program is provided in