Based on kernel version 3.16. Page generated on 2014-08-06 21:41 EST.
1 High Precision Event Timer Driver for Linux 2 3 The High Precision Event Timer (HPET) hardware follows a specification 4 by Intel and Microsoft which can be found at 5 6 http://www.intel.com/hardwaredesign/hpetspec_1.pdf 7 8 Each HPET has one fixed-rate counter (at 10+ MHz, hence "High Precision") 9 and up to 32 comparators. Normally three or more comparators are provided, 10 each of which can generate oneshot interrupts and at least one of which has 11 additional hardware to support periodic interrupts. The comparators are 12 also called "timers", which can be misleading since usually timers are 13 independent of each other ... these share a counter, complicating resets. 14 15 HPET devices can support two interrupt routing modes. In one mode, the 16 comparators are additional interrupt sources with no particular system 17 role. Many x86 BIOS writers don't route HPET interrupts at all, which 18 prevents use of that mode. They support the other "legacy replacement" 19 mode where the first two comparators block interrupts from 8254 timers 20 and from the RTC. 21 22 The driver supports detection of HPET driver allocation and initialization 23 of the HPET before the driver module_init routine is called. This enables 24 platform code which uses timer 0 or 1 as the main timer to intercept HPET 25 initialization. An example of this initialization can be found in 26 arch/x86/kernel/hpet.c. 27 28 The driver provides a userspace API which resembles the API found in the 29 RTC driver framework. An example user space program is provided in 30 file:Documentation/timers/hpet_example.c