.\"	$OpenBSD: acpicpu.4,v 1.10 2022/10/21 04:02:16 guenther Exp $
.\"
.\" Copyright (c) 2006 Michael Knudsen <mk@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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.\"
.Dd $Mdocdate: October 21 2022 $
.Dt ACPICPU 4
.Os
.Sh NAME
.Nm acpicpu
.Nd ACPI processor power and performance state
.Sh SYNOPSIS
.Cd "acpicpu* at acpi?"
.Sh DESCRIPTION
The
.Nm
driver provides support for extracting processor power and performance
levels from ACPI tables.
This information is used to enter deeper CPU power states when idle,
and can be used to throttle processor speed to reduce
power usage and extend battery life through the
.Va hw.setperf
.Xr sysctl 2
mechanism.
.Pp
.Nm
reports the C-states offered by ACPI using the format
.Dl C%d(%d@%d %s.%x@%#x)
where the respective fields are the ACPI state,
the reported power consumption,
the reported latency,
the method,
the flags on the method,
and the address for the method.
Inapplicable or unspecified fields are elided.
If the state won't be used for any reason then the entry will have a
.Sq !\&
prefix.
If the state is the fallback state used when no valid C-state entries were
found then flags will be a
.Sq !\& .
For the
.Va mwait
method the address is the hints value for the instruction.
.Sh SEE ALSO
.Xr sysctl 2 ,
.Xr acpi 4 ,
.Xr cpu 4 ,
.Xr intro 4 ,
.Xr apmd 8 ,
.Xr sysctl 8
.Sh HISTORY
The
.Nm
driver first appeared in
.Ox 3.9 .
.Sh AUTHORS
.An -nosplit
The
.Nm
driver was written by
.An Marco Peereboom Aq Mt marco@openbsd.org .
CPU power state (C-state) support was added by
.An Philip Guenther Aq Mt guenther@openbsd.org .