Datasheet

Power and Thermal Management

166 Datasheet

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 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 as identical to the C3 state, but in this

state the processor core voltage is lowered. There are no internal events in GMCH for the C4 state

that differ from the C3 state. (C4 state not supported by Intel Celeron M processor)

7.2 7.2. 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 state lost other than PCI config. system memory lost (optionally)

• D3 Cold – Power off

CPU:

• C0 Full On

• C1 Auto Halt

• C2 Stop Clock. Clk to CPU still running. Clock stopped to CPU core.

• C3 Deep Sleep. Clock to CPU stopped.

• C4 Deeper Sleep. Same as C3 with reduced voltage on the CPU.

System States:

• G0/S0 Full On

• G1/S1-M Power On Suspend (POS). System Context Preserved

• G1/S2 Not supported.

• G1/S3 Suspend to RAM (STR). Power and context lost to chipset.

• G1/S4 Suspend to Disk (STD). All power lost (except wakeup on ICH4-M)

• G2/S5 Soft off. Total reboot.