2010-09-15 04:51:07 +00:00
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.\" Copyright (c) 2009 Alexander Motin <mav@FreeBSD.org>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd September 14, 2010
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.Dt HPET 4
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.Os
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.Sh NAME
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.Nm hpet
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.Nd High Precision Event Timer driver
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.Sh SYNOPSIS
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To compile this driver into the kernel,
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place the following lines in your
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kernel configuration file:
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.Bd -ragged -offset indent
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.Cd "device acpi"
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.Ed
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.Pp
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The following tunables are settable from the
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.Xr loader 8 :
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.Bl -ohang
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.It Va hint.hpet. Ns Ar X Ns Va .allowed_irqs
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is a 32bit mask. Each set bit allows driver to use respective IRQ,
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if BIOS also set respective capability bit in comparator's configuration
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register.
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Default value is 0xffff0000, except some known broken hardware.
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.It Va hint.hpet. Ns Ar X Ns Va .clock
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controls event timers functionality support. Setting to 0, disables it.
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Default value is 1.
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.It Va hint.hpet. Ns Ar X Ns Va .legacy_route
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controls "LegacyReplacement Route" mode. If enabled, HPET will steal IRQ0 of
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i8254 timer and IRQ8 of RTC. Before using it, make sure that respective
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drivers are not using interrupts, by setting also:
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.Bd -literal
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hint.attimer.0.clock=0
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hint.atrtc.0.clock=0
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.Ed
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Default value is 0.
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.It Va hint.hpet. Ns Ar X Ns Va .per_cpu
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controls how much per-CPU event timers should driver attempt to register.
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This functionality requires every comparator in a group to have own unshared
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IRQ, so it depends on hardware capabilities and interrupts configuration.
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Default value is 1.
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.El
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.Sh DESCRIPTION
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This driver uses High Precision Event Timer hardware (part of the chipset,
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usually enumerated via ACPI) to supply kernel with one time counter and
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several (usually from 3 to 8) event timers.
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This hardware includes single main counter with known increment frequency
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(10MHz or more), and several programable comparators (optionally with
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automatic reload feature).
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When value of the main counter matches current value of any comparator,
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interrupt can be generated.
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Depending on hardware capabilities and configuration, interrupt can be
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delivered as regular I/O APIC interrupt (ISA or PCI) in range from 0 to 31,
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or as Front Side Bus interrupt, alike to PCI MSI interrupts, or in so called
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"LegacyReplacement Route" HPET can speal IRQ0 of i8254 and IRQ8 of the RTC.
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Interrupt can be either edge- or level-triggered. In last case they could be
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safely shared with PCI IRQs.
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Driver prefers to use FSB interrupts, if supported, to avoid sharing.
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If it is not possible, it uses single sharable IRQ from PCI range.
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Other modes (LegacyReplacement and ISA IRQs) require special care to setup,
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but could be configured manually via device hints.
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.Pp
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Event timers provided by the driver support both one-shot an periodic modes
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and irrelevant to CPU power states.
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.Pp
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Depending on hardware capabilities and configuration, driver can expose each
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comparator as separate event timer or group them into one or several per-CPU
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event timers. In last case interrupt of every of those comparators within
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group is bound to specific CPU core. This is possible only when each
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of these comparators has own unsharable IRQ.
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.Sh SEE ALSO
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.Xr acpi 4 ,
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2010-09-15 07:04:14 +00:00
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.Xr eventtimers 7
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2010-09-15 04:51:07 +00:00
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.Sh HISTORY
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The
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.Nm
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driver first appeared in
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.Fx 6.3 .
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Support for event timers was added in
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.Fx 9.0 .
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