.\" Copyright (c) 2010 Alexander Motin <mav@FreeBSD.org>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $FreeBSD: releng/12.2/share/man/man4/atrtc.4 330835 2018-03-13 09:42:33Z royger $
.\"
.Dd September 17, 2010
.Dt ATRTC 4
.Os
.Sh NAME
.Nm atrtc
.Nd AT Real-Time Clock (RTC) driver
.Sh SYNOPSIS
This driver is a mandatory part of i386/amd64 kernels.
.Pp
The following tunables are settable from the
.Xr loader 8 :
.Bl -ohang
.It Va hint.atrtc. Ns Ar X Ns Va .clock
controls event timers functionality support.
Setting to 0, disables it.
Default value is 1.
.It Va hw.atrtc.enable
Forces enabling or disabling of the device(s).
Setting to 0 disables it, setting to 1 enables it, bypassing any platform
configuration hints.
Default value is -1 (autodetect).
.El
.Sh DESCRIPTION
This driver uses RTC hardware to supply kernel with time-of-day clock
with 1 second resolution and one event timer.
This hardware uses base frequency of 32768Hz for advancing time-of-day clock
and generating periodic interrupts.
Interrupts could be generated with fixed number of frequencies, from 2Hz to
8192Hz, obtained by dividing base frequency by one of supported power-of-2
divisors.
.Pp
Event timer provided by the driver is irrelevant to CPU power states.
.Sh SEE ALSO
.Xr apic 4 ,
.Xr attimer 4 ,
.Xr eventtimers 4 ,
.Xr hpet 4