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<table class="head">
<tr>
<td class="head-ltitle">HPET(4)</td>
<td class="head-vol">Device Drivers Manual</td>
<td class="head-rtitle">HPET(4)</td>
</tr>
</table>
<div class="manual-text">
<section class="Sh">
<h1 class="Sh" id="NAME"><a class="permalink" href="#NAME">NAME</a></h1>
<p class="Pp"><code class="Nm">hpet</code> — <span class="Nd">High
Precision Event Timer driver</span></p>
</section>
<section class="Sh">
<h1 class="Sh" id="SYNOPSIS"><a class="permalink" href="#SYNOPSIS">SYNOPSIS</a></h1>
<p class="Pp">To compile this driver into the kernel, place the following lines
in your kernel configuration file:</p>
<div class="Bd Pp Bd-indent"><code class="Cd">device acpi</code></div>
<p class="Pp">The following tunables are settable from the
<a class="Xr">loader(8)</a>:</p>
<dl class="Bl-ohang">
<dt id="hint.hpet."><var class="Va">hint.hpet.</var><var class="Ar">X</var><var class="Va">.allowed_irqs</var></dt>
<dd>is a 32bit mask. Each set bit allows driver to use respective IRQ, if BIOS
also set respective capability bit in comparator's configuration register.
Default value is 0xffff0000, except some known broken hardware.</dd>
<dt id="hint.hpet.~2"><var class="Va">hint.hpet.</var><var class="Ar">X</var><var class="Va">.clock</var></dt>
<dd>controls event timers functionality support. Setting to 0, disables it.
Default value is 1.</dd>
<dt id="hint.hpet.~3"><var class="Va">hint.hpet.</var><var class="Ar">X</var><var class="Va">.legacy_route</var></dt>
<dd>controls "LegacyReplacement Route" mode. If enabled, HPET will
steal IRQ0 of i8254 timer and IRQ8 of RTC. Before using it, make sure that
respective drivers are not using interrupts, by setting also:
<div class="Bd Pp Li">
<pre>hint.attimer.0.clock=0
hint.atrtc.0.clock=0</pre>
</div>
Default value is 0.</dd>
<dt id="hint.hpet.~4"><var class="Va">hint.hpet.</var><var class="Ar">X</var><var class="Va">.per_cpu</var></dt>
<dd>controls how much per-CPU event timers should driver attempt to register.
This functionality requires every comparator in a group to have own
unshared IRQ, so it depends on hardware capabilities and interrupts
configuration. Default value is 1.</dd>
</dl>
</section>
<section class="Sh">
<h1 class="Sh" id="DESCRIPTION"><a class="permalink" href="#DESCRIPTION">DESCRIPTION</a></h1>
<p class="Pp">This driver uses High Precision Event Timer hardware (part of the
chipset, usually enumerated via ACPI) to supply kernel with one time counter
and several (usually from 3 to 8) event timers. This hardware includes
single main counter with known increment frequency (10MHz or more), and
several programmable comparators (optionally with automatic reload feature).
When value of the main counter matches current value of any comparator,
interrupt can be generated. Depending on hardware capabilities and
configuration, interrupt can be delivered as regular I/O APIC interrupt (ISA
or PCI) in range from 0 to 31, or as Front Side Bus interrupt, alike to PCI
MSI interrupts, or in so called "LegacyReplacement Route" HPET can
steal IRQ0 of i8254 and IRQ8 of the RTC. Interrupt can be either edge- or
level-triggered. In last case they could be safely shared with PCI IRQs.
Driver prefers to use FSB interrupts, if supported, to avoid sharing. If it
is not possible, it uses single sharable IRQ from PCI range. Other modes
(LegacyReplacement and ISA IRQs) require special care to setup, but could be
configured manually via device hints.</p>
<p class="Pp">Event timers provided by the driver support both one-shot an
periodic modes and irrelevant to CPU power states.</p>
<p class="Pp">Depending on hardware capabilities and configuration, driver can
expose each comparator as separate event timer or group them into one or
several per-CPU event timers. In last case interrupt of every of those
comparators within group is bound to specific CPU core. This is possible
only when each of these comparators has own unsharable IRQ.</p>
</section>
<section class="Sh">
<h1 class="Sh" id="SEE_ALSO"><a class="permalink" href="#SEE_ALSO">SEE
ALSO</a></h1>
<p class="Pp"><a class="Xr">acpi(4)</a>, <a class="Xr">apic(4)</a>,
<a class="Xr">atrtc(4)</a>, <a class="Xr">attimer(4)</a>,
<a class="Xr">eventtimers(4)</a>, <a class="Xr">timecounters(4)</a></p>
</section>
<section class="Sh">
<h1 class="Sh" id="HISTORY"><a class="permalink" href="#HISTORY">HISTORY</a></h1>
<p class="Pp">The <code class="Nm">hpet</code> driver first appeared in
<span class="Ux">FreeBSD 6.3</span>. Support for event timers was added in
<span class="Ux">FreeBSD 9.0</span>.</p>
</section>
</div>
<table class="foot">
<tr>
<td class="foot-date">September 14, 2010</td>
<td class="foot-os">FreeBSD 15.0</td>
</tr>
</table>
|
