IFB Power Management

16.2.5ACPI Bits Not Implemented by IFB

Many ACPI registers and bits are optional, and do not have to be implemented for a standard desktop design. Table 16-4shows which bits are not implemented by IFB.

Table 16-4. ACPI Bits Not Implemented in IFB

Offset

Register Name/Function

Comment

 

 

 

00-01h

PM1 Status

 

 

 

 

 

 

4

BM_STS

Not needed for standard desktop.

 

 

 

 

04-05h

PM1 Control

 

 

 

 

 

 

1

BM_RLD

Stopping CPU clock not supported.

 

 

 

 

0C-0Dh

General Purpose Status

 

 

 

 

 

 

9

GPI_STS

GPI not needed for desktop

 

 

 

 

 

11

LID_STS

Lid not needed for desktop

 

 

 

 

OE-0Fh

General Purpose Enables

 

 

 

 

 

 

9

GPI_EN

GPI not needed for desktop

 

 

 

 

 

11

LID_EN

Lid not needed for desktop

 

 

 

 

15h

Level 3 Register

Power state not needed for desktop

 

 

 

 

 

 

 

 

16.2.6Entry/Exit for the S4 and S5 States

As part of the ACPI spec, as well as PC’97 specs, all new desktop systems must support the SOFT OFF (ACPI S5) state. The state will have the following characteristics:

No system context preserved.

Power shut to all subsystems except RTC and wake logic (typically just the power button).

All system clocks shut except 32.768 kHz internal to the RTC logic.

There are two ways to enter the Soft-Off state:

1.The CPU will write a value of 100 to the SLP_TYP field and set the SLP_EN bit to 1.

2.The power button is pressed for 4 seconds. This is known as a power-button override event.

In either case, the entry to the Soft-Off state is done by asserting the SUSB and SUSC signals. This will cause the power to be shut and the PWROK signal is assumed to go low.

Note also that there is no need to enter the Soft-Off state gracefully. The STPCLK# and

SUS_STAT# signals don’t have to be asserted in any particular order, since the CPU and memory controller will be reset after the system is rebooted.

16-4

Intel® 460GX Chipset Software Developer’s Manual