acpi -- Advanced Configuration and Power Management support
The acpi driver provides support for the Intel/Microsoft/Compaq/Toshiba
ACPI standard. This support includes platform hardware discovery (superseding
the PnP and PCI BIOS), as well as power management (superseding
APM) and other features. ACPI core support is provided by the ACPI CA
reference implementation from Intel.
Note that the acpi driver is automatically loaded by the bootloader, and
should not normally be compiled into the kernel.
This support is still experimental, and thus there are many debugging and
tuning options which are managed via the kernel environment space, and
set in the loader(8) before booting the kernel.
Debugging is separated between layers and levels, where a layer is a portion
of the ACPI subsystem, and a level is a particular kind of debugging
Both layers and levels are specified as a whitespace-separated list of
tokens, with layers listed in debug.acpi.layer and levels in
debug.acpi.level. The supported layers are:
The supported levels are:
Selection of the appropriate layer and level values is important to avoid
massive amounts of debugging output. Check the code to see which you
Debugging output by the ACPI CA subsystem is prefixed with the module
name in lowercase, followed by a source line number. Output from the
FreeBSD-local code follows the same format, but the module name is uppercased.
To disable the acpi driver completely, set the kernel environment variable
hint.acpi.0.disabled to 1. Some i386 machines totally fail to operate
with some or all of ACPI disabled. Other i386 machines fail with
ACPI enabled. Non-i386 platforms do not support operating systems which
do not use ACPI. Disabling all or part of ACPI on non-i386 platforms may
result in a non-functional system.
The acpi driver comprises a set of drivers, which may be selectively disabled
in case of problems. To disable a sub-driver, list it in the kernel
environment variable debug.acpi.disable.
ACPI sub-devices and features that can be disabled:
bus (feature) Probes and attaches subdevices. Disabling will avoid
scanning the ACPI namespace entirely.
children (feature) Attaches standard ACPI sub-drivers and devices enumerated
in the ACPI namespace. Disabling this has a similar
effect to disabling ``bus'', except that the ACPI namespace
will still be scanned.
button (device) Supports ACPI button devices (typically power and
ec (device) Supports the ACPI Embedded Controller interface, used
to communicate with embedded platform controllers.
isa (device) Supports an ISA bus bridge defined in the ACPI namespace,
typically as a child of a PCI bus.
lid (device) Supports an ACPI laptop lid switch, which typically
puts a system to sleep.
pci (device) Supports Host to PCI bridges.
cpu (device) Supports CPU power-saving and speed-setting functions.
thermal (device) Supports system cooling and heat management.
timer (device) Implements a timecounter using the ACPI fixed-frequency
It is also possible to avoid portions of the ACPI namespace which may be
causing problems, by listing the full path of the root of the region to
be avoided in the kernel environment variable debug.acpi.avoid. The
object and all of its children will be ignored during the bus/children
scan of the namespace. The ACPI CA code will still know about the
OVERRIDING YOUR BIOS BYTECODE [Toc] [Back]
ACPI interprets bytecode named AML, ACPI Machine Language, provided by
the BIOS vendor as a memory image at boot time. Sometimes, the AML code
contains a problem that does not appear in the Microsoft implementation.
So we provide a way to override it with your own AML code.
In order to load your AML code, you must edit /boot/loader.conf and
include the following lines.
acpi_dsdt_name="/boot/acpi_dsdt.aml" #You may change the name.
In order to prepare your AML code, you will need the acpidump(8) and
iasl(1) utilities and some ACPI knowledge.
Enables loading of a custom ACPI DSDT.
Name of the DSDT table to load, if loading is enabled.
Selectively disables portions of ACPI for debugging purposes.
Disables all of ACPI.
Delay in milliseconds to wait for the EC to respond. Try
increasing this number if you get the error
Enables calling the VESA reset BIOS vector on the resume path.
Some graphic chips have problems such as LCD white-out after
resume. Try setting this to 0 if this causes problems for you.
Some systems' ASL may have problems because they look for names
of Microsoft operating systems. This tunable overrides the value
of the "\_OS" object from its default of "FreeBSD".
Override the interrupt to use.
Turn on verbose debugging information about what ACPI is doing.
Sets the speed of the CPU, if it supports multiple speeds, while
in the performance power profile.
Sets the speed of the CPU, if it supports multiple speeds, while
in the economy power profile.
Debugging information listing all sleep states and the number of
long and short sleeps for each one. The counters are reset when
hw.acpi.cpu.cx_lowest is modified.
Zero-based index of the lowest CPU idle state to use. A scheduling
algorithm will select between 0...index for the state to use
during the next sleep. To enable ACPI CPU idling control,
machdep.cpu_idle_hlt must be set to 1.
List of supported CPU idle states and their transition latency in
microseconds. Each state has a type, C1-3. C1 is equivalent to
the ia32 HLT instruction, C2 provides a deeper sleep with the
same semantics, and C3 provides the deepest sleep but additionally
requires bus mastering to be disabled. Deeper sleeps provide
more power savings but increased transition latency when an
ACPI is only found and supported on i386/ia32, ia64, and amd64.
loader.conf(5), acpiconf(8), acpidump(8), config(8), iasl(8)
Compaq Computer Corporation, Intel Corporation, Microsoft Corporation,
Phoenix Technologies Ltd., and Toshiba Corporation, Advanced
Configuration and Power Interface Specification, August 25, 2003,
The ACPI CA subsystem is developed and maintained by Intel Architecture
The following people made notable contributions to the ACPI subsystem in
FreeBSD: Michael Smith, Takanori Watanabe <takawata@jp.FreeBSD.org>,
Mitsuru IWASAKI <iwasaki@jp.FreeBSD.org>, Munehiro Matsuda, Nate Lawson,
the ACPI-jp mailing list at <acpi-jp@jp.FreeBSD.org>, and many other contributors.
This manual page was written by Michael Smith <msmith@FreeBSD.org>.
If the acpi driver is loaded as a module when it is already linked as
part of the kernel, odd things may happen.
FreeBSD 5.2.1 July 2, 2001 FreeBSD 5.2.1 [ Back ]