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82801AA and 82801AB Datasheet
5-61
Functional Description
Controlling Leakage and Power Consumption During Low-Power States
To control leakage in the system, various signals tri-state or go low during some low-power states.
General principles:
All signals going to powered down planes (either internally or externally) must be either
tri-stated or driven low.
Signals with pull-up resistors should not be low during low-power states. This is to avoid the
power consumed in the pull-up resistor.
Buses should be halted (and held) in a known state to avoid a floating input. (perhaps to some
other device) Floating inputs can cause extra power consumption.
Based on the above principles, the following measures are taken:
During C2 or S3state, the processor signals that have pull-ups are tri-stated.
During S3, all signals attached to powered down planes are tri-stated or driven low.
5.12.10
Clock Generators
The clock generator is expected to provide the frequencies shown in
Table 5-47
.
5.12.11
Legacy Power Management Theory of Operation
Instead of relying on ACPI software, legacy power management uses BIOS and various hardware
mechanisms. The ICH has a greatly simplified method for legacy power management compared
with previous generations.
The scheme relies on the concept of detecting when individual subsystems are idle, detecting when
the whole system is idle, and detecting accesses are attempted to idle subsystems.
However, the OS is assumed to be at least APM enabled. Without APM calls, there is no quick way
to know when the system is idle between keystrokes. The ICH does not support the burst modes
found in previous components.
APM Power Management
The ICH has a timer that, when enabled by the 1MIN_EN bit in the SMI Control and Enable
register, generates an SMI# once per minute. The SMI handler can check for system activity by
reading the DEVACT_STS register. If none of the system bits are set, the SMI handler can
increment a software counter. When the counter reaches a sufficient number of consecutive
minutes with no activity, the SMI handler can then put the system into a lower power state.
Table 5-47. ICH Input Clocks
Clock Name
Frequency
Event
CLK48
48.00000 MHz
This should be running in C0, C1, C2. Stops based on SLP_S3# being active.
CLK14
14.31818 MHz
This should be running in C0, C1, C2. Stop based on SLP_S3# being active.
CLK66
66.66667 MHz
This should be running in C0, C1, C2. Stops based on SLP_S3# being active
APIC_CLK
16.67 MHz
This should be running in C0, C1, C2. Stops based on SLP_S3# being active.
PCICLK
33.33333 MHz
The PCI clock starts/ stops based on the S3, S4, or S5 states. The PCI clock
is assumed always to be running in S0-S1 states.