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IFB Power Management
16-4 Intel® 460GX Chipset Software Developer’s Manual
16.2.5 ACPI 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 16-4 shows which bits are not implemented by IFB.
16.2.6 Entry/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.
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