ACPI#Global states

The firmware-level ACPI has three main components: the ACPI tables, the ACPI BIOS, and the ACPI registers. The ACPI BIOS generates ACPI tables and loads ACPI tables into main memory. Much of the firmware ACPI functionality is provided in bytecode of ACPI Machine Language (AML), a Turing-complete, domain-specific low-level language, stored in the ACPI tables.{{cite web| url = https://os.inf.tu-dresden.de/papers_ps/tr-atare-2009.pdf| title = ATARE: ACPI Tables and Regular Expressions| author = Bernhard Kauer| date = August 2009 | access-date = 2019-02-18}} To make use of the ACPI tables, the operating system must have an interpreter for the AML bytecode. A reference AML interpreter implementation is provided by the ACPI Component Architecture (ACPICA). At the BIOS development time, AML bytecode is compiled from the ASL (ACPI Source Language) code.[https://www.kernel.org/doc/ols/2005/ols2005v1-pages-59-76.pdf ACPI in Linux], 2005

The ACPI Component Architecture (ACPICA), mainly written by Intel's engineers, provides an open-source platform-independent reference implementation of the operating system–related ACPI code.[http://www.acpica.org/ ACPICA: ACPI Component Architecture] The ACPICA code is used by Linux, Haiku, ArcaOS{{cite web|url=https://www.arcanoae.com/wp-content/uploads/wiki/ReadMe-ACPI.txt|website=arcanoae.com|title=Readme for the ACPI Driver Package|access-date=2020-09-06}} and FreeBSD,[http://www.usenix.org/events/usenix02/tech/freenix/full_papers/watanabe/watanabe.ps ACPI implementation on FreeBSD - Usenix] which supplement it with their operating-system specific code.

{{anchor|1.0|1.0a|1.0b|2.0|2.0a|2.0b|2.0c}}The first revision of the ACPI specification was released in December 1996, supporting 16, 24 and 32-bit addressing spaces. It was not until August 2000 that ACPI received 64-bit address support as well as support for multiprocessor workstations and servers with revision 2.0.

In 1999, then Microsoft CEO Bill Gates stated in an e-mail that Linux would benefit from ACPI without them having to do work and suggested to make it Windows-only.{{Cite web |title=Microsoft wollte ACPI nur für Windows |url=https://www.derstandard.at/story/2843846/microsoft-wollte-acpi-nur-fuer-windows |access-date=2022-11-06 |website=Der Standard |language=de-AT}}{{Cite web |title=Microsoft: ACPI sollte nur unter Windows funktionieren |url=https://www.golem.de/0704/51686.html |access-date=2022-11-06 |website=Golem.de}}{{Cite web |last=Gates |first=Bill |date=1999-01-24 |title=ACPI extensions |url=http://www.iowaconsumercase.org/011607/3000/PX03020.pdf |url-status=dead |archive-url=https://web.archive.org/web/20070202174648/http://www.iowaconsumercase.org/011607/3000/PX03020.pdf |archive-date=2007-02-02}}

{{anchor|3.0|3.0a|3.0b}}In September 2004, revision 3.0 was released, bringing to the ACPI specification support for SATA interfaces, PCI Express bus, multiprocessor support for more than 256 processors, ambient light sensors and user-presence devices, as well as extending the thermal model beyond the previous processor-centric support.

{{anchor|4.0|4.0a}}Released in June 2009, revision 4.0 of the ACPI specification added various new features to the design; most notable are the USB 3.0 support, logical processor idling support, and x2APIC support.

{{anchor|5.0|5.0a|5.1}}Initially ACPI was exclusive to x86 architecture; Revision 5.0 of the ACPI specification was released in December 2011,{{cite web

| url = http://acpi.info/DOWNLOADS/ACPIspec50.pdf

| title = Advanced Configuration and Power Interface Specification (Revision 5.0)

| author1 = Hewlett-Packard

| author1-link = Hewlett-Packard

| author2 = Intel Corporation

| author2-link = Intel Corporation

| author3 = Microsoft

| author3-link = Microsoft

| author4 = Phoenix Technologies

| author4-link = Phoenix Technologies

| author5 = Toshiba

| author5-link = Toshiba

| date = 2011-12-06

| access-date = 2013-11-17

| website = acpi.info

| archive-date = September 14, 2012

| archive-url = https://web.archive.org/web/20120914012029/http://www.acpi.info/DOWNLOADS/ACPIspec50.pdf

| url-status = dead

}} which added the ARM architecture support. The revision 5.1 was released in July 2014.{{cite web

| url = http://www.uefi.org/sites/default/files/resources/ACPI_5_1release.pdf

| title = Advanced Configuration and Power Interface Specification (Revision 5.1)

| date = 2014-07-23 | access-date = 2015-05-24

| website = uefi.org }}

{{anchor|6.0|6.5}}The latest specification revision is 6.5, which was released in August 2022.

File:LOGOS.SYS.png

File:Windows_NT_4.0_NonACPI_Shutdown.png

File:Windows 10 Safe to shutdown screen.png

Microsoft's Windows 98 was the first operating system to implement ACPI,{{cite web |url=ftp://ftp.physik.hu-berlin.de/pub/driver/grafik/armada1120/RMF98/DISK1/WINDOW~1.PDF |title=Limitations When Using Microsoft Windows 98 on Compaq Armada Portables |page=3 |date=October 1998 |access-date=2014-01-27 |publisher=physik.hu-berlin.de}}{{Dead link|date=May 2019 |bot=InternetArchiveBot |fix-attempted=yes}}{{cite web |url=http://support.lenovo.com/en_US/guides-and-manuals/detail.page?&LegacyDocID=LWIK-3VJLL8 |archive-url=https://web.archive.org/web/20140203005405/http://support.lenovo.com/en_US/guides-and-manuals/detail.page?&LegacyDocID=LWIK-3VJLL8 |url-status=dead |archive-date=2014-02-03 |title=Windows 98 on ThinkPad systems - ThinkPad General |publisher=Support.lenovo.com |access-date=2014-01-27}} but its implementation was somewhat buggy or incomplete,{{cite book |author1=Robert Cowart |author2=Brian Knittel |title=Using Microsoft Windows 2000 Professional |url=https://archive.org/details/usingmicrosoftwi00cowa |url-access=registration |date=2000 |publisher=Que Publishing |isbn=978-0-7897-2125-9 |page=[https://archive.org/details/usingmicrosoftwi00cowa/page/30 30]}}[http://support.microsoft.com/kb/189091 Windows 98 Does Not Support ACPI Passive Cooling Mode] although some of the problems associated with it were caused by the first-generation ACPI hardware.{{cite web |archive-url=https://web.archive.org/web/19991013055230/http://winmag.com/library/1998/1201/cov0066.htm |archive-date=October 13, 1999 |website=winmag.com |url=http://winmag.com/library/1998/1201/cov0066.htm |title=Cover Story: Win98 Bugs & Fixes - December 1998 |url-status=dead}} Other operating systems, including later versions of Windows, macOS (x86 macOS only), eComStation, ArcaOS,{{cite web |url=https://www.arcanoae.com/wp-content/uploads/wiki/ArcaOS-changes.txt |title=ArcaOS Changelog |access-date=2020-08-24}} FreeBSD (since FreeBSD 5.0{{Cite web |title=FreeBSD 5.0-RELEASE Announcement |url=https://www.freebsd.org/releases/5.0R/announce.html |access-date=2020-12-03 |website=www.freebsd.org}}), NetBSD (since NetBSD 1.6{{Cite web |title=acpi(4) - NetBSD Manual Pages |url=https://man.netbsd.org/acpi.4 |access-date=2020-12-03 |website=man.netbsd.org}}), OpenBSD (since OpenBSD 3.8{{Cite web |title=acpi(4) - OpenBSD manual pages |url=https://man.openbsd.org/acpi.4 |access-date=2020-12-03 |website=man.openbsd.org}}), HP-UX, OpenVMS, Linux, GNU/Hurd and PC versions of Solaris, have at least some support for ACPI.{{cite web| title = ACPI 2.0 Specification Technical Review, Intel Developer Forum| url = http://www.acpi.info/presentations/acpi2M0800IDF.ppt| date = 2000-01-06| first = Guy | last = Therien| publisher = Intel Corporation| access-date = 2011-08-21| format = PPT| archive-url= https://web.archive.org/web/20110721184817/http://www.acpi.info/presentations/acpi2M0800IDF.ppt | archive-date=July 21, 2011 | url-status= live}} Some newer operating systems, like Windows Vista, require the computer to have an ACPI-compliant BIOS, and since Windows 8, the S0ix/Modern Standby state was implemented.{{cite web | url = http://download.microsoft.com/download/5/b/9/5b97017b-e28a-4bae-ba48-174cf47d23cd/CPA002_WH06.ppt| format = PPT| title = ACPI in Windows Vista| first = Allen | last = Marshall| publisher = Microsoft Corporation| access-date = 2010-07-02}}

Windows operating systems use acpi.sys{{cite web| title = Acpi.sys: The Windows ACPI Driver| url = https://docs.microsoft.com/en-us/windows-hardware/drivers/kernel/acpi-driver| date = 2017-06-15| publisher = Microsoft Corporation| access-date = 2019-09-20}} to access ACPI events.

The 2.4 series of the Linux kernel had only minimal support for ACPI, with better support implemented (and enabled by default) from kernel version 2.6.0 onwards.[https://www.kernel.org/doc/ols/2004/ols2004v1-pages-121-132.pdf The State of ACPI in the Linux Kernel] Old ACPI BIOS implementations tend to be quite buggy, and consequently are not supported by later operating systems. For example, Windows 2000, Windows XP, and Windows Server 2003 only use ACPI if the BIOS date is after January 1, 1999.[https://msdn.microsoft.com/en-us/library/windows/hardware/ff540487(v=vs.85).aspx ACPI BIOS]. msdn.microsoft.com. Similarly, Linux kernel 2.6 may not use ACPI if the BIOS date is before January 1, 2001.

Linux-based operating systems can provide handling of ACPI events via acpid.{{Cite book |url=https://www.worldcat.org/oclc/773210086 |title=Linux in a nutshell |date=2005 |publisher=O'Reilly |last1=Siever |first1=Ellen |last2=Weber |first2=Aaron |last3=Figgins |first3=Stephen |last4=Love |first4=Robert |last5=Robbins |first5=Arnold |isbn=978-0-596-52949-9 |edition=5th |location=Sebastopol, California |page=36 |oclc=773210086}}

Once an OSPM-compatible operating system activates ACPI, it takes exclusive control of all aspects of power management and device configuration. The OSPM implementation must expose an ACPI-compatible environment to device drivers, which exposes certain system, device and processor states.

The ACPI Specification defines the following four global "Gx" states and six sleep "Sx" states for an ACPI-compliant computer system:ACPI Spec Rev 5.0 - dated December 6, 2011{{cite web| url = http://www.anandtech.com/show/6355/intels-haswell-architecture/3| title = Intel's Haswell Architecture Analyzed| date = 2012-10-05 | access-date = 2013-10-20| author = Anand Lal Shimpi | publisher = AnandTech}}

{{anchor|Legacy}}The specification also defines a Legacy state: the state of an operating system which does not support ACPI. In this state, the hardware and power are not managed via ACPI, effectively disabling ACPI.

The device states D0–D3 are device dependent:

• D0 or Fully On is the operating state.
• As with S0ix, Intel has D0ix states for intermediate levels on the SoC.{{cite web |title=D0ix States |url=https://software.intel.com/en-us/energy-analysis-user-guide-d0ix-states |website=software.intel.com |language=en |date=9 March 2020}}
• D1 and D2 are intermediate power-states whose definition varies by device.
• D3: The D3 state is further divided into D3 Hot (has auxiliary power), and D3 Cold (no power provided):
• Hot: A device can assert power management requests to transition to higher power states.
• Cold or Off has the device powered off and unresponsive to its bus.

The CPU power states C0–C3 are defined as follows:

• C0 is the operating state.
• C1 (often known as Halt) is a state where the processor is not executing instructions, but can return to an executing state essentially instantaneously. All ACPI-conformant processors must support this power state. Some processors, such as the Pentium 4 and AMD Athlon, also support an Enhanced C1 state (C1E or Enhanced Halt State) for lower power consumption, however this proved to be buggy on some systems.{{cite web|title=Athlon II X2: Hardware C1E and Return of the CnQ Bug| publisher = AnandTech|url=https://www.anandtech.com/show/2775/2|access-date=2020-10-26}}{{cite web| title = Intel's Pentium 4 600 series processors| first = Scott | last = Wasson| date = 2005-02-21| page = 2| publisher = The Tech Report| url = http://techreport.com/articles.x/7998/2}}
• C2 (often known as Stop-Clock) is a state where the processor maintains all software-visible state, but may take longer to wake up. This processor state is optional.
• C3 (often known as Sleep) is a state where the processor does not need to keep its cache coherent, but maintains other state. Some processors have variations on the C3 state (Deep Sleep, Deeper Sleep, etc.) that differ in how long it takes to wake the processor. This processor state is optional.
• Additional states are defined by manufacturers for some processors. For example, Intel's Haswell platform has states up to C10, where it distinguishes core states and package states.{{cite web| url = http://images.anandtech.com/reviews/cpu/intel/Haswell/ULT/c10.png| title = Processor Package and Core C-States| date = 2013-06-09 | access-date = 2013-10-20| publisher = AnandTech}}

While a device or processor operates (D0 and C0, respectively), it can be in one of several power-performance states. These states are implementation-dependent. P0 is always the highest-performance state, with P1 to Pn being successively lower-performance states. The total number of states is device or processor dependent, but can be no greater than 16.{{cite web| url = http://www.acpi.info/DOWNLOADS/ACPIspec30.pdf| title = Advanced Configuration and Power Interface Specification, Revision 3.0, Section 2.6 Device and Processor Performance State Definitions| date = 2004-09-02| access-date = 2015-08-19| website = ACPI.info| page = 23| archive-date = November 28, 2015| archive-url = https://web.archive.org/web/20151128143452/http://www.acpi.info/DOWNLOADS/ACPIspec30.pdf| url-status = dead}}

P-states have become known as SpeedStep in Intel processors, as PowerNow! or Cool'n'Quiet in AMD processors, and as PowerSaver in VIA processors.

• P0 maximum power and frequency
• P1 less than P0, voltage and frequency scaled
• P2 less than P1, voltage and frequency scaledLink aggregation
• Pn less than P(n–1), voltage and frequency scaled

ACPI-compliant systems interact with hardware through either a "Function Fixed Hardware (FFH) Interface", or a platform-independent hardware programming model which relies on platform-specific ACPI Machine Language (AML) provided by the original equipment manufacturer (OEM).

Function Fixed Hardware interfaces are platform-specific features, provided by platform manufacturers for the purposes of performance and failure recovery. Standard Intel-based PCs have a fixed function interface defined by Intel,{{cite web| url = ftp://download.intel.com/technology/iapc/acpi/downloads/30222305.pdf| archive-url = https://web.archive.org/web/20121225022426/http://download.intel.com/technology/IAPC/acpi/downloads/30222305.pdf| title = Intel Processor Vendor-Specific ACPI| author = Intel Corporation| author-link = Intel Corporation| date = September 2006| access-date = 2014-10-05| archive-date = 2012-12-25

}} which provides a set of core functionality that reduces an ACPI-compliant system's need for full driver stacks for providing basic functionality during boot time or in the case of major system failure.

ACPI Platform Error Interface (APEI) is a specification for reporting of hardware errors, e.g. chipset, RAM to the operating system.

ACPI defines many tables that provide the interface between an ACPI-compliant operating system and system firmware (BIOS or UEFI). This includes RSDP, RSDT, XSDT, FADT, FACS, DSDT, SSDT, MADT, and MCFG, for example.

{{cite journal

| citeseerx = 10.1.1.173.2206

| title = ACPI in Linux

| first = Len

| last = Brown

| date = 2005-07-20

| journal = Ottawa Linux Symposium

| page = 3

}}

{{Cite web|title=ACPI Tables — The Linux Kernel documentation|url=https://www.kernel.org/doc/html/latest/arm64/acpi_object_usage.html|access-date=2020-11-08|website=www.kernel.org|archive-date=October 20, 2020|archive-url=https://web.archive.org/web/20201020091509/https://www.kernel.org/doc/html/latest/arm64/acpi_object_usage.html|url-status=dead}}

The tables allow description of system hardware in a platform-independent manner, and are presented as either fixed-formatted data structures or in AML. The main AML table is the DSDT (differentiated system description table). The AML can be decompiled by tools like Intel's iASL (open-source, part of ACPICA) for purposes like patching the tables for expanding OS compatibility.{{cite web |title=DSDT |url=https://wiki.archlinux.org/index.php/DSDT |website=ArchWiki}}{{cite web |title=Getting Started With ACPI|url=https://khronokernel.github.io/Getting-Started-With-ACPI/ |website=GitBook}}

The Root System Description Pointer (RSDP) is located in a platform-dependent manner, and describes the rest of the tables.

A custom ACPI table called the Windows Platform Binary Table (WPBT) is used by Microsoft to allow vendors to add software into the Windows OS automatically. Some vendors, such as Lenovo, have been caught using this feature to install harmful software such as Superfish.{{cite web |last1=Hoffman |first1=Chris |date=August 19, 2015 |title=Zombie Crapware: How the Windows Platform Binary Table Works |url=https://www.howtogeek.com/226308/the-windows-platform-binary-table-why-crapware-can-come-back-after-a-clean-install/ |website=How-To Geek}} Samsung shipped PCs with Windows Update disabled. Windows versions older than Windows 7 do not support this feature, but alternative techniques can be used. This behavior has been compared to rootkits.{{cite web |title=Vendors 'rootkit': 'Windows Platform Binary Table' (WPBT) |url=https://borncity.com/win/2017/12/06/vendors-rootkit-windows-platform-binary-table-wpbt/ |website=Born's Tech and Windows World |date=December 6, 2017}}{{Cite web |author1=Mayank Sharma |date=2021-09-27 |title=Millions of Windows 10 PCs exposed by nasty security vulnerability |url=https://www.techradar.com/news/nasty-security-vulnerability-exposes-millions-of-windows-10-pcs |access-date=2022-11-10 |website=TechRadar |language=en}}

In November 2003, Linus Torvalds—author of the Linux kernel—described ACPI as "a complete design disaster in every way".Linux Magazine issue 162, May 2014, page 9{{cite web |last=Searls |first=Doc |date=2003-11-25 |title=Linus & the Lunatics, Part II |url=http://www.linuxjournal.com/article/7279 |access-date=2010-01-13 |publisher=Linux Journal}}

• Active State Power Management
• Coreboot
• Devicetree
• Green computing
• Power management keys
• Server Base System Architecture (SBSA)
• Wake-on-LAN

• {{cite web|url=https://mjg59.dreamwidth.org/68350.html|title=Why ACPI?|first1=Matthew|last1=Garrett|author-link=Matthew Garrett|date=2023-10-31}}

{{Reflist}}

• {{Official website|https://uefi.org/specifications}} (UEFI and ACPI specifications)
• [http://www.hardwaresecrets.com/everything-you-need-to-know-about-the-cpu-c-states-power-saving-modes/ Everything You Need to Know About the CPU C-States Power Saving Modes]
• [http://www.virtualbox.org/svn/vbox/trunk/src/VBox/Devices/EFI/Firmware/OvmfPkg/AcpiTables/ Sample EFI ASL code] {{Webarchive|url=https://web.archive.org/web/20230412142524/http://www.virtualbox.org/svn/vbox/trunk/src/VBox/Devices/EFI/Firmware/OvmfPkg/AcpiTables/ |date=April 12, 2023 }} used by VirtualBox; EFI/ASL code itself is from the open source Intel EFI Development Kit II (TianoCore)
• [https://acpica.org ACPICA]

{{Firmware and booting}}{{Computer processor power management technologies}}

{{CPU technologies}}

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