Datasheet

Functional Description

Datasheet 205

• The GMCH also reduces I/O power dynamically, by disabling sense amps on input buffers,

as well as tri-stating output buffers when possible

• Dynamic Clock Power Down reduces power in all modes of operation

• Enhanced Intel SpeedStep technology

• Flat Panel Power Sequencing

5.8 General Description of Supported CPU States

C0 (Full On): This is the only state that runs software. All clocks are running, STPCLK is

deasserted, and the processor core is active. The processor can service snoops and maintain cache

coherency in this state.

C1 (Auto Halt): The first level of power reduction occurs when the processor executes an Auto-

Halt instruction. This stops the execution of the instruction stream and reduces the processor’s

power consumption. The processor can service snoops and maintain cache coherency in this state.

C2 (Stop Grant): To enter this low power state, STPCLK is asserted. The processor can still

service snoops and maintain cache coherency in this state.

C3 (Sleep or Deep Sleep): In these states the processor clock is stopped. The GMCH/MCH

assumes that no hub interface cycles (except special cycles) will occur while the GMCH/MCH is

in this state. The processor cannot snoop its caches to maintain coherency while in the C3 state.

The GMCH/MCH will transition from the C0 state to the C3 state when software reads the Level

3 Register. This is an ACPI defined register but BIOS or APM (via BIOS) can use this facility

when entering a low power state. The Host Clock PLL within the GMCH/MCH can be

programmed to be shut off for increased power savings and the GMCH uses the DPSLP signal

input for this purpose.

C4 (Deeper Sleep): The C4 state appears to the GMCH/MCH as identical to the C3 state, but in

this state the processor core voltage is lowered. There are no internal events in GMCH/MCH for

the C4 state that differ from the C3 state.

5.9 General Description of ACPI States

Internal Graphics Adapter:

• D0 Full on, display active

• D1 Low power state, low latency recovery. No display, system memory retained

• D3 Hot - All states lost other than PCI configuration. system memory lost (optionally)

• D3 Cold - Power off

CPU:

• C0 Full On

• C1 Auto Halt