Initial import

1 files changed, 30 insertions, 0 deletions

diff --git a/Documentation/timers/hpet.txt b/Documentation/timers/hpet.txt
new file mode 100644
index 000000000..767392ffd
--- /dev/null
+++ b/Documentation/timers/hpet.txt
@@ -0,0 +1,30 @@
+		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
+
+	http://www.intel.com/hardwaredesign/hpetspec_1.pdf
+
+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:Documentation/timers/hpet_example.c