88 lines
3.2 KiB
Groff
88 lines
3.2 KiB
Groff
.\" 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.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd May 26, 2014
|
|
.Dt ATTIMER 4
|
|
.Os
|
|
.Sh NAME
|
|
.Nm attimer
|
|
.Nd i8254 Programmable Interval Timer (AT Timer) driver
|
|
.Sh SYNOPSIS
|
|
This driver is a mandatory part of x86 kernels.
|
|
.Pp
|
|
The following tunables are settable from the
|
|
.Xr loader 8 :
|
|
.Bl -ohang
|
|
.It Va hint.attimer. Ns Ar X Ns Va .clock
|
|
controls support for the event timer functionality.
|
|
Setting this value to
|
|
.Dv 0
|
|
disables it.
|
|
The default value is
|
|
.Dv 1 .
|
|
.It Va hint.attimer. Ns Ar X Ns Va .timecounter
|
|
controls support for the time counter functionality.
|
|
Setting this value to
|
|
.Dv 0
|
|
disables it.
|
|
The default value is
|
|
.Dv 1 .
|
|
.It Va hw.i8254.freq
|
|
allows overriding the default counter frequency.
|
|
The same value is also available at run-time via the
|
|
.Va machdep.i8254_freq
|
|
sysctl.
|
|
.El
|
|
.Sh DESCRIPTION
|
|
This driver uses i8254 Programmable Interval Timer (AT Timer) hardware
|
|
to supply the kernel with one timecounter and one event timer, and to generate
|
|
sound tones for the system speaker.
|
|
This hardware includes three channels.
|
|
Each channel includes a 16 bit counter which decreases with a known,
|
|
platform-dependent frequency.
|
|
Counters can operate in several different modes, including periodic and
|
|
one-shot.
|
|
The output of each channel has platform-defined wiring: one channel is wired
|
|
to the interrupt controller and may be used as event timer, one channel is
|
|
wired to the speaker and used to generate sound tones, and one timer is reserved
|
|
for platform purposes.
|
|
.Pp
|
|
The
|
|
.Nm
|
|
driver uses a single hardware channel to provide both time counter and event
|
|
timer functionality.
|
|
To make this possible, the respective counter must be running in periodic mode.
|
|
As a result, the one-shot event timer mode is supported only when time counter
|
|
functionality is disabled.
|
|
.Pp
|
|
The event timer provided by the driver is irrelevant to CPU power states.
|
|
.Sh SEE ALSO
|
|
.Xr apic 4 ,
|
|
.Xr atrtc 4 ,
|
|
.Xr eventtimers 4 ,
|
|
.Xr hpet 4 ,
|
|
.Xr timecounters 4
|