.\"
.\" Copyright (c) 2007, 2008, 2009 Rui Paulo <rpaulo@FreeBSD.org>
.\" Copyright (c) 2026 Enji Cooper <ngie@FreeBSD.org>
.\"
.\" SPDX-License-Identifier: BSD-2-Clause
.\"
.Dd September 6, 2026
.Dt ASMC 4
.Os
.Sh NAME
.Nm asmc
.Nd Apple System Management Controller driver
.Sh SYNOPSIS
To compile this driver into the kernel, place the following line in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd device asmc
.Sh DESCRIPTION
The
.Nm
driver controls the Apple System Management Controller (SMC for short)
found on Intel Apple systems.
.Pp
With this driver, you can configure your keyboard backlight
brightness, check temperatures of several sensors, check the speed of
the internal fans and check the status of the Sudden Motion Sensor.
.Pp
Variables related to the SMC control and inspection are exported via
.Xr sysctl 3
under the device tree
.Va dev.asmc .
.Sh KEYBOARD BACKLIGHT
The keyboard brightness on all laptop models, e.g., MacBook Pro, can be
controlled by writing a value to the
.Va dev.asmc.%d.light.control
sysctl MIB or with
.Xr backlight 8
utility.
.Pp
The following sysctl MIBs contains the raw value returned by the left
and right light sensors:
.Va dev.asmc.%d.light.left
or
.Va dev.asmc.%d.light.right .
.Sh TEMPERATURES
The number of temperature sensors and their description varies among
systems.
You can inspect the temperature sensors on your system by traversing
the
.Va dev.asmc.temp
sysctl MIB.
.Pp
All values are in degrees celsius.
.Sh SYSTEM FANS
The
.Va dev.asmc.fan.%d
sysctl tree contains the leaf nodes
.Va speed ,
.Va safespeed ,
.Va minspeed ,
.Va maxspeed
and
.Va targetspeed .
Each of these leaf nodes represent the current fan speed, the safest
minimum fan speed, the minimum speed and the maximum speed
respectively.
.Pp
All values are in RPM.
.Sh POWER MANAGEMENT
The
.Va dev.asmc.%d.auto_poweron
sysctl controls whether the machine automatically powers on when AC power
is restored after an unclean power loss
.Pq SMC key Dq AUPO .
A value of 1 enables automatic power-on; 0 disables it.
.Sh RAW SMC KEY ACCESS
When the kernel is compiled with the
.Dv ASMC_DEBUG
option, a set of sysctl nodes is provided under
.Va dev.asmc.%d.raw
for reading and writing arbitrary SMC keys by name.
.Pp
.Bl -tag -width "dev.asmc.%d.raw.value" -compact
.It Va dev.asmc.%d.raw.key
Set the 4-character SMC key name to access (e.g.,\&
.Dq AUPO ) .
Setting this automatically queries the key's length and type.
.It Va dev.asmc.%d.raw.value
Read or write the key's value as a hex string.
.It Va dev.asmc.%d.raw.len
The auto-detected value length in bytes (read-only).
.It Va dev.asmc.%d.raw.type
The 4-character SMC type string (e.g.,\&
.Dq ui8 ,
.Dq flt )
(read-only).
.El
.Pp
Example usage:
.Bd -literal -offset indent
sysctl dev.asmc.0.raw.key=AUPO
sysctl dev.asmc.0.raw.value
sysctl dev.asmc.0.raw.value=01
.Ed
.Sh SUDDEN MOTION SENSOR
The Sudden Motion Sensor (SMS for short) is a device that detects
laptop movement and notifies the operating system via an interrupt.
The sysctl MIBs present under
.Va dev.asmc.sms
all relate to the SMS.
.Pp
The most interesting usage of this device is to park the disk heads
when the laptop is moved harshly.
Configure
.Xr devd 8
the following way to automatically park your hard drives using
.Xr camcontrol 8 :
.Bd -literal -offset indent
notify 0 {
	match "system"		"ACPI";
	match "subsystem"	"asmc";
	action			"/sbin/camcontrol idle X";
};
.Ed
.Pp
Do not forget to change
.Ar X
in the command example to match the target hard drive, e.g.,
.Pa ada0 .
.Pp
Also, please note that parking the disk heads too many times can
dramatically reduce your hard drive's life span.
Do not rely solely on the SMS to protect your hard drive: good care and
common sense can increase your hard drive's life.
.Sh HARDWARE
The
.Nm
driver supports the Apple SMC on the following systems:
.Pp
.Bl -bullet -offset indent -compact
.It
iMac
.It
MacBook
.It
MacBook Air
.It
MacBook Pro
.It
Mac Mini
.It
Mac Pro
.El
.Sh FILES
.Bl -tag -width "/dev/backlight/asmc0" -compact
.It Pa /dev/backlight/asmc0
Keyboard
.Xr backlight 8
device node.
.Sh SEE ALSO
.Xr apple_bce 4 ,
.Xr backlight 8 ,
.Xr camcontrol 8 ,
.Xr devd 8 ,
.Xr sysctl 8
.Sh HISTORY
The
.Nm
driver first appeared in
.Fx 8.0 .
The driver was heavily modified in
.Fx 15.1
to support additional Apple SMC functionality and platforms.
.Sh AUTHORS
.An Rui Paulo Aq Mt rpaulo@FreeBSD.org
wrote
.Nm
as a 2007 Google Summer of Code project.
.Sh BUGS
This driver also supports ARM64 Mac models (in theory), but this has not
been tested yet.