1.\" Copyright (c) 2010 Alexander Motin <mav@FreeBSD.org> 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.\" $FreeBSD$ 26.\" 27.Dd December 15, 2022 28.Dt ATRTC 4 29.Os 30.Sh NAME 31.Nm atrtc 32.Nd AT Real-Time Clock (RTC) driver 33.Sh SYNOPSIS 34This driver is a mandatory part of i386/amd64 kernels. 35.Pp 36The following tunables are settable from the 37.Xr loader 8 : 38.Bl -ohang 39.It Va hint.atrtc. Ns Ar X Ns Va .clock 40controls event timers functionality support. 41Setting to 0, disables it. 42Default value is 1. 43.It Va hw.atrtc.enabled 44Forces enabling or disabling of the device(s). 45Setting to 0 disables it, setting to 1 enables it, bypassing any platform 46configuration hints. 47Default value is -1 (autodetect). 48.El 49.Sh DESCRIPTION 50This driver uses RTC hardware to supply kernel with time-of-day clock 51with 1 second resolution and one event timer. 52This hardware uses base frequency of 32768Hz for advancing time-of-day clock 53and generating periodic interrupts. 54Interrupts could be generated with fixed number of frequencies, from 2Hz to 558192Hz, obtained by dividing base frequency by one of supported power-of-2 56divisors. 57.Pp 58Event timer provided by the driver is irrelevant to CPU power states. 59.Sh SEE ALSO 60.Xr apic 4 , 61.Xr attimer 4 , 62.Xr eventtimers 4 , 63.Xr hpet 4 64