Product Description
37
1.12 Power Management
Power management is implemented at several levels, including:
• Software support through Advanced Configuration and Power Interface (ACPI)
• Hardware support
1.12.1 ACPI
ACPI gives the operating system direct control over the power management and Plug
and Play functions of a computer. The use of ACPI with this board requires an
operating system that provides full ACPI support. ACPI features include:
• Plug and Play (including bus and device enumeration)
• Power management control of individual devices, add-in boards (some add-in
boards may require an ACPI-aware driver), video displays, and hard disk drives
• Methods for achieving less than 15-watt system operation in the power-on/standby
sleeping state
• A Soft-off feature that enables the operating system to power-off the computer
• Support for multiple wake-up events (see Table 10 on page 39)
• Support for a front panel power and sleep mode switch
Table 8 lists the system states based on how long the power switch is pressed,
depending on how ACPI is configured with an ACPI-aware operating system.
Table 8. Effects of Pressing the Power Switch
If the system is in this
state…
…and the power switch is
pressed for
…the system enters this state
Off
(ACPI G2/G5 – Soft off)
Less than four seconds Power-on
(ACPI G0 – working state)
On
(ACPI G0 – working state)
Less than four seconds Soft-off/Standby
(ACPI G1 – sleeping state)
On
(ACPI G0 – working state)
More than six seconds Fail safe power-off
(ACPI G2/G5 – Soft off)
Sleep
(ACPI G1 – sleeping state)
Less than four seconds Wake-up
(ACPI G0 – working state)
Sleep
(ACPI G1 – sleeping state)
More than six seconds Power-off
(ACPI G2/G5 – Soft off)
1.12.1.1 System States and Power States
Under ACPI, the operating system directs all system and device power state
transitions. The operating system puts devices in and out of low-power states based
on user preferences and knowledge of how devices are being used by applications.
Devices that are not being used can be turned off. The operating system uses
information from applications and user settings to put the system as a whole into a
low-power state.
Table 9 lists the power states supported by the board along with the associated system
power targets. See the ACPI specification for a complete description of the various
system and power states.
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