SB82371 Intel Corporation, SB82371 Datasheet - Page 108

• Manufacturer Part Number: SB82371
• Description: 82371FB (PIIX) AND 82371SB (PIIX3) PCI ISA IDE XCELERATOR
• Manufacturer: Intel Corporation

82371FB (PIIX) AND 82371SB (PIIX3)
3.12.
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.
108
Power Management
EXTSMI#, RTC Alarm,
(Mouse, Keyboard,
ComPort Activity,
Fast On Event
APM Call)
Power Switch
Turned Off
Figure 10. Fast On/Off Flow
Fast Off
Power
Power
Off
On
(Timer Expires,
Power Switch
Fast Off Event
RTC Alarm,
Turned On
APM Call)
EXTSMI#,
Power Switch
Turned Off
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