IFB Power Management

16

16.1Overview

IFB is designed for desktop systems, and includes the following power management features for the desktop design:

1.Compliance with industry standard specifications: APM Rev 1.2

ACPI Rev 1.0

Energy Star (30W idle)

PCI Power Management Rev 1.0

2.ACPI S1 Sleep State with STPCLK# and/or SLP# active.

3.ACPI S4/S5 Sleep States (Suspend-to-Disk and Soft-Off).

4.ACPI Power management timer.

5.APCI Compliant Power Button and Thermal Input signals.

6.Ability for firmware to cause SCI and ACPI software to cause SMI#: ACPI Requirement.

7.SMI# and/or SCI generation from various sources, including power management timer.

8.Alt Access Mode: Needed to allow for Suspend-to-Disk.

Table 16-1shows the power states defined for platforms using the IFB.

Table 16-1. IFB Power States and Consumption

ACPI State/

Description

Substate

 

 

 

S0/C0

ON: CPU operating a full speed with no latencies.

 

 

S0/C1

Auto Halt: CPU has executed a Halt instruction. Returns to the S0/C0 state based on

 

a break event.

 

 

S1

Stop-Grant or Sleep: IFB supports two versions of the S1 Sleep state. In the first the

 

STPCLK# signal is active, much like the S0 state. In the 2nd, both STPCLK# and SLP#

 

are active. This puts the CPU in an even lower power state, but it cannot maintain

 

cache coherency. Entrance to the S1 state is performed by a write to the SLP_EN bit

 

with the appropriate SLP_TYP field. Will return to S0 state based on Wake event.

 

 

S4

Suspend to Disk (STD): The context of the system is maintained on the disk. All

 

power is then shut to the system except for the logic required to resume. Entrance to

 

the S4 state is performed by a write to the SLP_EN bit with the appropriate SLP_TYP

 

field. Will return to S0 state based on Wake event.

 

 

S5

Soft Off (SOFF): No system context saved.These two states are similar. For STD

 

(ACPI S4 state), SOFF (ACPI S5 or G2 states) is the same, except the context is not

 

saved. Entrance to the S5 state is performed either by a write to the SLP_EN bit with

 

the appropriate SLP_TYP field, or by a power button override. Will return to S0 state

 

based on Wake event.

 

 

G3

Power Failure (PFAIL): Power is lost to the system (typically because it has been

 

unplugged). IFB still maintains the RTC and CMOS RAM with the external backup

 

battery. Return after power resumption depends on AFTERG3 bit and state prior to the

 

power failure.

 

 

Intel® 460GX Chipset Software Developer’s Manual

16-1