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ACPI(4)			 BSD Kernel Interfaces Manual		       ACPI(4)

     acpi -- Advanced Configuration and	Power Management support

     device acpi

     options ACPI_DEBUG
     options DDB

     The acpi driver provides support for the Intel/Microsoft/Compaq/Toshiba
     ACPI standard.  This support includes platform hardware discovery (super-
     seding 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 loader(8), and
     should only be compiled into the kernel on	platforms where	ACPI is	manda-

     The acpi driver is	intended to provide power management without user in-
     tervention.  If the default settings are not optimal, the following
     sysctls can be used to modify or monitor acpi behavior.

	     Enable dumping Debug objects without options ACPI_DEBUG.  Default
	     is	0, ignore Debug	objects.

	     AC	line state (1 means online, 0 means on battery power).

	     Debugging information listing the percent of total	usage for each
	     sleep state.  The values are reset	when hw.acpi.cpu.cx_lowest is

	     Lowest Cx state to	use for	idling the CPU.	 A scheduling algo-
	     rithm will	select states between C1 and this setting as system
	     load dictates.  To	enable ACPI CPU	idling control,	machdep.idle
	     should be set to acpi if it is listed in machdep.idle_available

	     List of supported CPU idle	states and their transition latency in
	     microseconds.  Each state has a type (e.g., C2).  C1 is equiva-
	     lent to the ia32 HLT instruction, C2 provides a deeper sleep with
	     the same semantics, and C3	provides the deepest sleep but addi-
	     tionally requires bus mastering to	be disabled.  States greater
	     than C3 provide even more power savings with the same semantics
	     as	the C3 state.  Deeper sleeps provide more power	savings	but
	     increased transition latency when an interrupt occurs.

	     Disable ACPI during the reboot process.  Most systems reboot fine
	     with ACPI still enabled, but some require exiting to legacy mode
	     first.  Default is	0, leave ACPI enabled.

	     Use the ACPI Reset	Register capability to reboot the system.
	     Some newer	systems	require	use of this register, while some only
	     work with legacy rebooting	support.

	     Suspend state (S1-S5) to enter when the lid switch	(i.e., a note-
	     book screen) is closed.  Default is "NONE"	(do nothing).

	     Suspend state (S1-S5) to enter when the power button is pressed.
	     Default is	S5 (power-off nicely).

	     Reset the video adapter from real mode during the resume path.
	     Some systems need this help, others have display problems if it
	     is	enabled.  Default is 0 (disabled).

	     Indicate whether the system supports S4BIOS.  This	means that the
	     BIOS can handle all the functions of suspending the system	to
	     disk.  Otherwise, the OS is responsible for suspending to disk
	     (S4OS).  Most current systems do not support S4BIOS.

	     Suspend state (S1-S5) to enter when the sleep button is pressed.
	     This is usually a special function	button on the keyboard.	 De-
	     fault is S3 (suspend-to-RAM).

	     Wait this number of seconds between preparing the system to sus-
	     pend and actually entering	the suspend state.  Default is 1 sec-

	     Suspend states (S1-S5) supported by the BIOS.

	     S1	     Quick suspend to RAM.  The	CPU enters a lower power
		     state, but	most peripherals are left running.

	     S2	     Lower power state than S1,	but with the same basic	char-
		     acteristics.  Not supported by many systems.

	     S3	     Suspend to	RAM.  Most devices are powered off, and	the
		     system stops running except for memory refresh.

	     S4	     Suspend to	disk.  All devices are powered off, and	the
		     system stops running.  When resuming, the system starts
		     as	if from	a cold power on.  Not yet supported by FreeBSD
		     unless S4BIOS is available.

	     S5	     System shuts down cleanly and powers off.

	     Enable verbose printing from the various ACPI subsystems.

     Tunables can be set at the	loader(8) prompt before	booting	the kernel or
     stored in /boot/loader.conf.  Many	of these tunables also have a matching
     sysctl(8) entry for access	after boot.

	     Enables loading of	a custom ACPI DSDT.

	     Name of the DSDT table to load, if	loading	is enabled.

	     Do	not use	the MADT to match ACPI Processor objects to CPUs.
	     This is needed on a few systems with a buggy BIOS that does not
	     use consistent processor IDs.  Default is 0 (disabled).

	     Selectively disables portions of ACPI for debugging purposes.

	     Enable less strict	ACPI implementations.  Default is 1, ignore
	     common BIOS mistakes.

	     Specify the number	of task	threads	that are started on boot.
	     Limiting this to 1	may help work around various BIOSes that can-
	     not handle	parallel requests.  The	default	value is 3.

	     Override any automatic quirks completely.

	     Beep the PC speaker on resume.  This can help diagnose sus-
	     pend/resume problems.  Default is 0 (disabled).

	     Set this to 1 to disable all of ACPI.  If ACPI has	been disabled
	     on	your system due	to a blacklist entry for your BIOS, you	can
	     set this to 0 to re-enable	ACPI for testing.
	     Delay in milliseconds to wait for the EC to respond.  Try in-
	     creasing this number if you get the error

	     Override the assumed memory starting address for PCI host

     hw.acpi.install_interface,	hw.acpi.remove_interface
	     Install or	remove OS interface(s) to control return value of
	     `_OSI' query method.  When	an OS interface	is specified in
	     hw.acpi.install_interface,	_OSI query for the interface returns
	     it	is supported.  Conversely, when	an OS interface	is specified
	     in	hw.acpi.remove_interface, _OSI query returns it	is not
	     supported.	 Multiple interfaces can be specified in a comma-sepa-
	     rated list	and any	leading	white spaces will be ignored.  For ex-
	     ample, "FreeBSD, Linux" is	a valid	list of	two interfaces
	     "FreeBSD" and "Linux".

	     Enables calling the VESA reset BIOS vector	on the resume path.
	     This can fix some graphics	cards that have	problems such as LCD
	     white-out after resume.  Default is 0 (disabled).

	     Allow override of whether methods execute in parallel or not.
	     Enable this for serial behavior, which fixes "AE_ALREADY_EXISTS"
	     errors for	AML that really	cannot handle parallel method execu-
	     tion.  It is off by default since this breaks recursive methods
	     and some IBMs use such code.

	     Turn on verbose debugging information about what ACPI is doing.
	     Override the interrupt to use for this link and index.  This ca-
	     pability should be	used carefully,	and only if a device is	not
	     working with acpi enabled.	 "%s" is the name of the link (e.g.,
	     LNKA).  "%d" is the resource index	when the link supports multi-
	     ple IRQs.	Most PCI links only have one IRQ resource, so the be-
	     low form should be	used.
	     Override the interrupt to use.  This capability should be used
	     carefully,	and only if a device is	not working with acpi enabled.
	     "%s" is the name of the link (e.g., LNKA).

     Since ACPI	support	on different platforms varies greatly, there are many
     debugging and tuning options available.

     For machines known	not to work with acpi enabled, there is	a BIOS black-
     list.  Currently, the blacklist only controls whether acpi	should be dis-
     abled or not.  In the future, it will have	more granularity to control
     features (the infrastructure for that is already there).

     To	enable acpi (for debugging purposes, etc.) on machines that are	on the
     blacklist,	set the	kernel environment variable hint.acpi.0.disabled to 0.
     Before trying this, consider updating your	BIOS to	a more recent version
     that may be compatible with ACPI.

     To	disable	the acpi driver	completely, set	the kernel environment vari-
     able hint.acpi.0.disabled to 1.

     Some i386 machines	totally	fail to	operate	with some or all of ACPI dis-
     abled.  Other i386	machines fail with ACPI	enabled.  Disabling all	or
     part of ACPI on non-i386 platforms	(i.e., platforms where ACPI support is
     mandatory)	may result in a	non-functional system.

     The acpi driver comprises a set of	drivers, which may be selectively dis-
     abled in case of problems.	 To disable a sub-driver, list it in the ker-
     nel environment variable debug.acpi.disabled.  Multiple entries can be
     listed, separated by a space.

     ACPI sub-devices and features that	can be disabled:

     all	  Disable all ACPI features and	devices.

     acad	  (device) Supports AC adapter.

     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 sim-
		  ilar effect to disabling "bus", except that the ACPI name-
		  space	will still be scanned.

     button	  (device) Supports ACPI button	devices	(typically power and
		  sleep	buttons).

     cmbat	  (device) Control-method batteries device.

     cpu	  (device) Supports CPU	power-saving and speed-setting func-

     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.

     quirks	  (feature) Do not honor quirks.  Quirks automatically disable
		  ACPI functionality based on the XSDT table's OEM vendor name
		  and revision date.

     pci	  (device) Supports Host to PCI	bridges.

     pci_link	  (feature) Performs PCI interrupt routing.

     sysresource  (device) Pseudo-devices containing resources which ACPI

     thermal	  (device) Supports system cooling and heat management.

     timer	  (device) Implements a	timecounter using the ACPI fixed-fre-
		  quency timer.

     video	  (device) Supports acpi_video(4) which	may conflict with
		  agp(4) device.

     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 ob-
     ject 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 avoided re-

     To	enable debugging output, acpi must be compiled with options
     ACPI_DEBUG.  Debugging output is separated	between	layers and levels,
     where a layer is a	component of the ACPI subsystem, and a level is	a par-
     ticular kind of debugging output.

     Both layers and levels are	specified as a whitespace-separated list of
     tokens, with layers listed	in debug.acpi.layer and	levels in

     The first set of layers is	for ACPI-CA components,	and the	second is for
     FreeBSD drivers.  The ACPI-CA layer descriptions include the prefix for
     the files they refer to.  The supported layers are:

     ACPI_UTILITIES	   Utility ("ut") functions
     ACPI_HARDWARE	   Hardware access ("hw")
     ACPI_EVENTS	   Event and GPE ("ev")
     ACPI_TABLES	   Table access	("tb")
     ACPI_NAMESPACE	   Namespace evaluation	("ns")
     ACPI_PARSER	   AML parser ("ps")
     ACPI_DISPATCHER	   Internal representation of interpreter state	("ds")
     ACPI_EXECUTER	   Execute AML methods ("ex")
     ACPI_RESOURCES	   Resource parsing ("rs")
     ACPI_CA_DEBUGGER	   Debugger implementation ("db", "dm")
     ACPI_OS_SERVICES	   Usermode support routines ("os")
     ACPI_CA_DISASSEMBLER  Disassembler	implementation (unused)
     ACPI_ALL_COMPONENTS   All the above ACPI-CA components
     ACPI_AC_ADAPTER	   AC adapter driver
     ACPI_BATTERY	   Control-method battery driver
     ACPI_BUS		   ACPI, ISA, and PCI bus drivers
     ACPI_BUTTON	   Power and sleep button driver
     ACPI_EC		   Embedded controller driver
     ACPI_FAN		   Fan driver
     ACPI_OEM		   Platform-specific driver for	hotkeys, LED, etc.
     ACPI_POWER		   Power resource driver
     ACPI_PROCESSOR	   CPU driver
     ACPI_THERMAL	   Thermal zone	driver
     ACPI_TIMER		   Timer driver
     ACPI_ALL_DRIVERS	   All the above FreeBSD ACPI drivers

     The supported levels are:

     ACPI_LV_INIT	      Initialization progress
     ACPI_LV_DEBUG_OBJECT     Stores to	objects
     ACPI_LV_INFO	      General information and progress
     ACPI_LV_REPAIR	      Repair a common problem with predefined methods
     ACPI_LV_ALL_EXCEPTIONS   All the previous levels
     ACPI_LV_VERBOSITY1	      All the previous levels
     ACPI_LV_VERBOSITY2	      All the previous levels
     ACPI_LV_ALL	      Synonym for "ACPI_LV_VERBOSITY2"
     ACPI_LV_VERBOSITY3	      All the previous levels
     ACPI_LV_VERBOSE	      All levels after "ACPI_LV_VERBOSITY3"

     Selection of the appropriate layer	and level values is important to avoid
     massive amounts of	debugging output.  For example,	the following configu-
     ration is a good way to gather initial information.  It enables debug
     output for	both ACPI-CA and the acpi driver, printing basic information
     about errors, warnings, and progress.


     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	upper-

     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	bug that does not appear when parsed by	the Microsoft imple-
     mentation.	 FreeBSD provides a way	to override it with your own AML code
     to	work around or debug such problems.  Note that all AML in your DSDT
     and any SSDT tables is overridden.

     In	order to load your AML code, you must edit /boot/loader.conf and in-
     clude the following lines.

	   acpi_dsdt_name="/boot/acpi_dsdt.aml"	# You may change this name.

     In	order to prepare your AML code,	you will need the acpidump(8) and
     iasl(8) utilities and some	ACPI knowledge.

     ACPI is only found	and supported on i386/ia32, ia64, and amd64.

     kenv(1), acpi_thermal(4), device.hints(5),	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 <>,
     Mitsuru IWASAKI <>, Munehiro	Matsuda, Nate Lawson,
     the ACPI-jp mailing list at <>, and many other con-

     This manual page was written by Michael Smith <>.

     Many BIOS versions	have serious bugs that may cause system	instability,
     break suspend/resume, or prevent devices from operating properly due to
     IRQ routing problems.  Upgrade your BIOS to the latest version available
     from the vendor before deciding it	is a problem with acpi.

     The acpi CPU idle power management	drive conflicts	with the local APIC
     (LAPIC) timer.  Disable the local APIC timer with hint.apic.0.clock=0 or
     do	not use	the C3 and deeper states if the	local APIC timer is enabled.

BSD				August 16, 2012				   BSD


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