forked from Qortal/Brooklyn
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
30 lines
1.5 KiB
30 lines
1.5 KiB
=========================================== |
|
High Precision Event Timer Driver for Linux |
|
=========================================== |
|
|
|
The High Precision Event Timer (HPET) hardware follows a specification |
|
by Intel and Microsoft, revision 1. |
|
|
|
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 |
|
arch/x86/kernel/hpet.c. |
|
|
|
The driver provides a userspace API which resembles the API found in the |
|
RTC driver framework. An example user space program is provided in |
|
file:samples/timers/hpet_example.c
|
|
|