General information about ACPI.

Here, specify when the system should wake from a sleep state. Currently, this feature is not fully supported.

Provides information about possible sleep states.

All events are reported here and processed by the Powersave daemon (powersaved). If no daemon accesses this file, events, such as a brief click on the power button or closing the lid, can be read with cat /proc/acpi/event (terminate with Ctrl-C).

These files contain the ACPI tables DSDT (differentiated system description table) and FADT (fixed ACPI description table). They can be read with acpidmp, acpidisasm, and dmdecode. These programs and their documentation are located in the package pmtools. For example, acpidmp DSDT | acpidisasm.

Shows whether the AC adapter is connected.

Detailed information about the battery state. The charge level is read by comparing the last full capacity from info with the remaining capacity from state. A more comfortable way to do this is to use one of the special programs introduced in Section 16.3.3, “ACPI Tools”. The charge level at which a battery event is triggered can be specified in alarm.

This directory contains information about various switches.

Shows if the fan is currently active. Activate or deactivate the fan manually by writing 0 (on) or 3 (off) into this file. However, both the ACPI code in the kernel and the hardware (or the BIOS) overwrite this setting when it gets too warm.

Information about the energy saving options of the processor.

Information about the current processor state. An asterisk next to C2 indicates that the processor is idle. This is the most frequent state, as can be seen from the usage value.

Can be used to set the throttling of the processor clock. Usually, throttling is possible in eight levels. This is independent of the frequency control of the CPU.

If the performance (outdated) and the throttling are automatically controlled by a daemon, the maximum limits can be specified here. Some of the limits are determined by the system. Some can be adjusted by the user.

A separate subdirectory exists for every thermal zone. A thermal zone is an area with similar thermal properties whose number and names are designated by the hardware manufacturer. However, many of the possibilities offered by ACPI are rarely implemented. Instead, the temperature control is handled conventionally by the BIOS. The operating system is not given much opportunity to intervene, because the life span of the hardware is at stake. Therefore, some of the following descriptions only have a theoretical value.

Current temperature of the thermal zone.

The state indicates if everything is ok or if ACPI applies active or passive cooling. In the case of ACPI-independent fan control, this state is always ok.

Select the cooling method controlled by ACPI. Choose from passive (less performance, economical) or active cooling mode (full performance, fan noise).

Enables the determination of temperature limits for triggering specific actions, like passive or active cooling, suspension (hot), or a shutdown (critical). The possible actions are defined in the DSDT (device-dependent). The trip points determined in the ACPI specification are critical, hot, passive, active1, and active2. Even if not all of them are implemented, they must always be entered in this file in this order. For example, the entry echo 90:0:70:0:0 > trip_points sets the temperature for critical to 90 and the temperature for passive to 70 (all temperatures measured in degrees Celsius).

If the value in temperature is not updated automatically when the temperature changes, toggle the polling mode here. The command echo X > /proc/acpi/thermal_zone/*/polling_frequency causes the temperature to be queried every X seconds. Set X=0 to disable polling.

PowerNow! and Speedstep are the designations AMD and Intel use for this technology. However, this technology is also applied in processors of other manufacturers. The clock frequency of the CPU and its core voltage are reduced at the same time, resulting in more than linear energy savings. This means that when the frequency is halved (half performance), far less than half of the energy is consumed. This technology is independent from APM or ACPI and requires a daemon that adapts the frequency and the current need for performance. The settings can be made in the directory /sys/devices/system/cpu/cpu*/cpufreq/.

This technology omits a certain percentage of the clock signal impulses for the CPU. At 25% throttling, every fourth impulse is omitted. At 87.5%, only every eighth impulse reaches the processor. However, the energy savings are a little less than linear. Normally, throttling is only used if frequency scaling is not available or to maximize power savings. This technology, too, must be controlled by a special process. The system interface is /proc/acpi/processor/*/throttling.

The operating system puts the processor to sleep whenever there is nothing to do. In this case, the operating system sends the CPU a halt command. There are three states: C1, C2, and C3. In the most economic state C3, even the synchronization of the processor cache with the main memory is halted. Therefore, this state can only be applied if no other device modifies the contents of the main memory via bus master activity. Some drivers prevent the use of C3. The current state is displayed in /proc/acpi/processor/*/power.

Do not use ACPI for configuring the PCI devices.

Only perform a simple resource configuration. Do not use ACPI for other purposes.

Disable ACPI.