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Intel
®
82854 Graphics Memory Controller Hub (GMCH)
148 D15343-003
7.1 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 assumes that
no Hub interface cycles (except special cycles) will occur while the GMCH is in this state. The
processor cannot snoop its caches to maintain coherency while in the C3 state. The GMCH 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. (The C4 state is not supported by the Intel Celeron M Processor, or
Genuine Intel Processor).
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-MPower On Suspend (POS). System Context Preserved
• G1/S2Not supported.
• G1/S3Suspend to RAM (STR). Power and context lost to chipset.
• G1/S4Suspend to Disk (STD). All power lost (except wakeup on ICH4-M)
• G2/S5Soft off. Total reboot.