82371FB Datasheet, PDF (108/122 Pages) Intel Corporation – 82371FB (PIIX) AND 82371SB (PIIX3) PCI ISA IDE XCELERATOR

82371FB (PIIX) AND 82371SB (PIIX3)
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3.12. Power Management
The PIIX/PIIX3 has extensive power management capability permitting a system to operate in a low power
state without being powered down. In a typical desktop personal computer there are two states — Power On
and Power-Off. Leaving a system powered on when not in use wastes power. The PIIX/PIIX3 provides a Fast
On/Off feature that creates a third state called Fast Off (Figure 10). When in the Fast Off state, the system
consumes less power than the Power-On state.
The PIIX's power management architecture is based on three functions—System Management Mode (SMM),
Clock Control, and Advanced Power Management (APM). Software (called SMM code) controls the
transitions between the Power On state and the Fast Off state. The PIIX/PIIX3 invokes this software by
generating an SMI to the CPU (asserting the SMI# signal). A variety of programmable events are provided
that can generate an SMI. The SMM code places the system in either the Power On state or the Fast Off
state.
A Fast On event is an event that instructs the computer (via an SMI to the CPU) to enter the Power-On state
in anticipation of system activity by the user. Fast On events are programmable and include moving the
mouse, pressing a key on the keyboard, an external hardware event, an incoming call to a system
FAX/Modem, a RTC alarm, or the operating system.
Power Switch
Turned Off
Fast On Event
(Mouse, Keyboard,
ComPort Activity,
EXTSMI#, RTC Alarm,
APM Call)
Power
Off
Power Switch
Turned Off
Power Switch
Turned On
Power
On
Fast Off Event
(Timer Expires,
EXTSMI#,
RTC Alarm,
APM Call)
Fast Off
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Figure 10. Fast On/Off Flow
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