1 .\" Copyright (c) 2010 Alexander Motin <mav@FreeBSD.org>
2 .\" All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
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.
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
32 .Nd AT Real-Time Clock (RTC) driver
34 This driver is a mandatory part of i386/amd64 kernels.
36 The following tunables are settable from the
39 .It Va hint.atrtc. Ns Ar X Ns Va .clock
40 controls event timers functionality support.
41 Setting to 0, disables it.
43 .It Va hw.atrtc.enabled
44 Forces enabling or disabling of the device(s).
45 Setting to 0 disables it, setting to 1 enables it, bypassing any platform
47 Default value is -1 (autodetect).
50 This driver uses RTC hardware to supply kernel with time-of-day clock
51 with 1 second resolution and one event timer.
52 This hardware uses base frequency of 32768Hz for advancing time-of-day clock
53 and generating periodic interrupts.
54 Interrupts could be generated with fixed number of frequencies, from 2Hz to
55 8192Hz, obtained by dividing base frequency by one of supported power-of-2
58 Event timer provided by the driver is irrelevant to CPU power states.