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58 lines
2.3 KiB
Groff
58 lines
2.3 KiB
Groff
.\" Copyright (c) 2010 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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd September 17, 2010
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.Dt ATRTC 4
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.Os
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.Sh NAME
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.Nm atrtc
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.Nd AT Real-Time Clock (RTC) driver
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.Sh SYNOPSIS
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This driver is a mandatory part of i386/amd64 kernels.
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.Pp
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The following tunable is settable from the
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.Xr loader 8 :
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.Bl -ohang
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.It Va hint.atrtc. 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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.El
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.Sh DESCRIPTION
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This driver uses RTC hardware to supply kernel with time-of-day clock
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with 1 second resolution and one event timer.
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This hardware uses base frequency of 32768Hz for advancing time-of-day clock
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and generating periodic interrupts.
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Interrupts could be generated with fixed number of frequencies, from 2Hz to
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8192Hz, obtained by dividing base frequency by one of supported power-of-2
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divisors.
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.Pp
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Event timer provided by the driver is irrelevant to CPU power states.
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.Sh SEE ALSO
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.Xr apic 4 ,
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.Xr attimer 4 ,
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.Xr eventtimers 4 ,
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.Xr hpet 4
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