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 September 14, 2010 28.Dt attimer 4 29.Os 30.Sh NAME 31.Nm attimer 32.Nd i8254 Programmable Interval Timer (AT Timer) driver 33.Sh SYNOPSIS 34This driver is a mandatory part of x86 kernels. 35.Pp 36The following tunables are settable from the 37.Xr loader 8 : 38.Bl -ohang 39.It Va hint.attimer. Ns Ar X Ns Va .clock 40controls event timers functionality support. Setting to 0, disables it. 41Default value is 1. 42.It Va hint.attimer. Ns Ar X Ns Va .timecounter 43controls time counter functionality support. Setting to 0, disables it. 44Default value is 1. 45.It Va hw.i8254.freq 46allows to override default counter frequency. 47The same value is also available in run-time via 48.Va machdep.i8254_freq 49sysctl. 50.El 51.Sh DESCRIPTION 52This driver uses i8254 Programmable Interval Timer (AT Timer) hardware 53to supply kernel with one time counter and one event timer, and generate 54sound tones for system speaker. 55This hardware includes three channels. 56Each channel includes 16bit counter, counting down with known, 57platform-dependent frequency. 58Counters can operate in several different modes, including periodic and 59one-shot. 60Output of each channel has platform-defined wiring: one channel is wired 61to the interrupt controller and may be used as event timer, one channel is 62wired to speaker and used to generate sound tones, and one timer is reserved 63for platform purposes. 64.Pp 65Driver uses single hardware channel to provide both time counter and event 66timer functionality. 67To make it possible, respective counter must be running in periodic more. 68As result, one-shot event timer mode supported only when time counter 69functionality is disabled. 70.Pp 71Event timer provided by the driver is irrelevant to CPU power states. 72.Sh SEE ALSO 73.Xr atrtc 4 , 74.Xr hpet 4 , 75.Xr eventtimers 7 76