Advanced Configuration and Power Interface Specification

ACPI Overview
component to avoid damage. If this occurs, the platform must notify OSPM of the performance
reduction if the reduction is of significant duration (in other words, if the duration of reduced
performance could adversely impact OSPM’s power or performance control policy - operating
system vendors can provide guidance in this area). The second exception is the case where the
platform contains Active cooling devices but does not contain Passive cooling temperature trip
points or controls,. In this case, a hardware based Active cooling mechanism may be implemented
without impacting OSPM’s goals. Any platform that requires both active and passive cooling must
allow OSPM to manage the platform thermals via ACPI defined active and passive cooling
interfaces.
3.1 System Power Management
Under OSPM, the OS directs all system and device power state transitions. Employing user
preferences and knowledge of how devices are being used by applications, the OS puts devices in
and out of low-power states. Devices that are not being used can be turned off. Similarly, the OS
uses information from applications and user settings to put the system as a whole into a low- power
state. The OS uses ACPI to control power state transitions in hardware.
3.2 Power States
From a user-visible level, the system can be thought of as being in one of the states in the following
diagram:
G3 -Mech
Off
Power
Failure/
Power Off
Modem HDD CDROM
D3 D3 D3
D2 D2 D2
D1 D1 D1
D0 D0 D0
C0
BIOS
Routine
Legacy
G0 (S0) -
Working
S4
S 3
S2
S1
Wake
Event
G1 -
Sleeping
G2 (S 5) -
Soft Off
Performance
State Px
CPU
Throttling
C0
C1
C2
Cn
Figure 3-2 Global System Power States and Transitions
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