31 строка
1.5 KiB
ReStructuredText
31 строка
1.5 KiB
ReStructuredText
|
===========================================
|
||
|
|
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
|