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Diffstat (limited to 'share/man/man4/attimer.4')
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diff --git a/share/man/man4/attimer.4 b/share/man/man4/attimer.4 new file mode 100644 index 000000000000..751b9ea1a203 --- /dev/null +++ b/share/man/man4/attimer.4 @@ -0,0 +1,77 @@ +.\" 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 September 14, 2010 +.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 event timers functionality support. Setting to 0, disables it. +Default value is 1. +.It Va hint.attimer. Ns Ar X Ns Va .timecounter +controls time counter functionality support. Setting to 0, disables it. +Default value is 1. +.It Va hw.i8254.freq +allows to override default counter frequency. +The same value is also available in run-time via +.Va machdep.i8254_freq +sysctl. +.El +.Sh DESCRIPTION +This driver uses i8254 Programmable Interval Timer (AT Timer) hardware +to supply kernel with one time counter and one event timer, and generate +sound tones for system speaker. +This hardware includes three channels. +Each channel includes 16bit counter, counting down with known, +platform-dependent frequency. +Counters can operate in several different modes, including periodic and +one-shot. +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 speaker and used to generate sound tones, and one timer is reserved +for platform purposes. +.Pp +Driver uses single hardware channel to provide both time counter and event +timer functionality. +To make it possible, respective counter must be running in periodic more. +As result, one-shot event timer mode supported only when time counter +functionality is disabled. +.Pp +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 |