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Intel® 460GX Chipset Software Developer’s Manual 16-1
IFB Power Management 16
16.1 Overview
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 16-1 shows the power states defined for platforms using the IFB.
Table 16-1. IFB Power States and Consumption
ACPI State/
Substate
Description
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 2
nd
, 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.