1 High Precision Event Timer Driver for Linux 2 3The High Precision Event Timer (HPET) hardware follows a specification 4by Intel and Microsoft, revision 1. 5 6Each HPET has one fixed-rate counter (at 10+ MHz, hence "High Precision") 7and up to 32 comparators. Normally three or more comparators are provided, 8each of which can generate oneshot interrupts and at least one of which has 9additional hardware to support periodic interrupts. The comparators are 10also called "timers", which can be misleading since usually timers are 11independent of each other ... these share a counter, complicating resets. 12 13HPET devices can support two interrupt routing modes. In one mode, the 14comparators are additional interrupt sources with no particular system 15role. Many x86 BIOS writers don't route HPET interrupts at all, which 16prevents use of that mode. They support the other "legacy replacement" 17mode where the first two comparators block interrupts from 8254 timers 18and from the RTC. 19 20The driver supports detection of HPET driver allocation and initialization 21of the HPET before the driver module_init routine is called. This enables 22platform code which uses timer 0 or 1 as the main timer to intercept HPET 23initialization. An example of this initialization can be found in 24arch/x86/kernel/hpet.c. 25 26The driver provides a userspace API which resembles the API found in the 27RTC driver framework. An example user space program is provided in 28file:samples/timers/hpet_example.c 29
