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
     (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 loader(8), and
     should only be compiled into the kernel on platforms where ACPI is

     The acpi driver is intended to provide power management without user
     intervention.  If the default settings are not optimal, the following
     sysctls can be used to modify or monitor acpi behavior.  Note that some
     variables will be available only if the given hardware supports them (such
     as hw.acpi.acline).

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

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

             Lowest Cx state to use for idling the CPU.  A scheduling algorithm
             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 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.  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.

             List of supported CPU idle states and their transition methods, as
             directed by the firmware.

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

             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
             notebook 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.  Default
             is S3 (suspend-to-RAM).

             Wait this number of seconds between preparing the system to suspend
             and actually entering the suspend state.  Default is 1 second.

             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
                     characteristics.  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 cannot
             handle parallel requests.  The default value is 3.

             Override any automatic quirks completely.

             Beep the PC speaker on resume.  This can help diagnose
             suspend/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
             increasing this number if you get the error

             Override the assumed memory starting address for PCI host bridges.

     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-separated list and
             any leading white spaces will be ignored.  For example, "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 execution.
             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
             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).  "%d" is the resource index when the link supports multiple
             IRQs.  Most PCI links only have one IRQ resource, so the below 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
     blacklist.  Currently, the blacklist only controls whether acpi should be
     disabled 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 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.  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
     disabled in case of problems.  To disable a sub-driver, list it in the
     kernel 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
                  similar effect to disabling “bus”, except that the ACPI
                  namespace 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

     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.

     mwait        (feature) Do not ask firmware for available x86-vendor
                  specific methods to enter Cx sleep states.  Only query and use
                  the generic I/O-based entrance method.  The knob is provided
                  to work around inconsistencies in the tables filled by

     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-
                  frequency timer.

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

     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 avoided region.

     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 particular 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
     configuration 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.

           debug.acpi.layer="ACPI_ALL_COMPONENTS ACPI_ALL_DRIVERS"

     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

     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
     implementation.  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 include
     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 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,

     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

     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.

BSD                                May 9, 2015                               BSD