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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> &#x2014; <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 &quot;LegacyReplacement Route&quot; 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 &quot;LegacyReplacement Route&quot; 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>