path: root/Documentation/timers/hpet.rst
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authorMauro Carvalho Chehab <>2019-06-12 14:53:00 -0300
committerJonathan Corbet <>2019-06-14 14:31:48 -0600
commit458f69ef36656dc74679667380422dd8063eabfb (patch)
treec44aafca54ae7d01160fe8ef09e7999594145a67 /Documentation/timers/hpet.rst
parent4ca9bc225e46eb7bc040dd948be7cb68975d80d3 (diff)
docs: timers: convert docs to ReST and rename to *.rst
The conversion here is really trivial: just a bunch of title markups and very few puntual changes is enough to make it to be parsed by Sphinx and generate a nice html. The conversion is actually: - add blank lines and identation in order to identify paragraphs; - fix tables markups; - add some lists markups; - mark literal blocks; - adjust title markups. At its new index.rst, let's add a :orphan: while this is not linked to the main index.rst file, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab <> Acked-by: Mark Brown <> Signed-off-by: Jonathan Corbet <>
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+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
+The driver provides a userspace API which resembles the API found in the
+RTC driver framework. An example user space program is provided in