82801DB Datasheet, PDF (135/587 Pages) Intel Corporation – Intel 82801DB I/O Controller Hub 4 (ICH4)

Functional Description
5.12 Power Management (D31:F0)
5.12.1
The power management features include:
• ACPI Power and Thermal Management Support
— ACPI 24-Bit Timer
— Software initiated throttling of processor performance for Thermal and Power Reduction
— Hardware Override to throttle processor performance if system too hot
— SCI and SMI# Generation
• PCI PME# Signal for Wake Up from Low-Power states
• System Clock Control
— ACPI C2 state: Stop-Grant state (using STPCLK# signal) halts processor’s instruction
stream
• System Sleeping State Control
— ACPI S1 state: Like C2 state (only STPCLK# active, and SLP# optional)
— ACPI S3 state: Suspend to RAM (STR)
— ACPI S4 state: Suspend-to-Disk (STD)
— ACPI G2/S5 state: Soft Off (SOFF)
— Power Failure Detection and Recovery
• Streamlined Legacy Power Management Support for APM-Based Systems
Intel^® ICH4 and System Power States
Table 5-35 shows the power states defined for ICH4-based platforms. The state names generally
match the corresponding ACPI states.
Table 5-35. General Power States for Systems Using Intel^® ICH4
State/
Substates
Legacy Name / Description
G0/S0/C0
G0/S0/C1
G0/S0/C2
G1/S1
G1/S3
G1/S4
G2/S5
G3
Full On: Processor operating. Individual devices may be shut down to save power. The different
processor operating levels are defined by Cx states, as shown in Table 5-36. Within the C0 state, the
Intel^® ICH4 can throttle the STPCLK# signal to reduce power consumption. The throttling can be
initiated by software or by the THRM# input signal.
Auto-Halt: Processor has executed a AutoHalt instruction and is not executing code. The processor
snoops the bus and maintains cache coherency.
Stop-Grant: The STPCLK# signal goes active to the processor. The processor performs a Stop-
Grant cycle, halts its instruction stream, and remains in that state until the STPCLK# signal goes
inactive. In the Stop-Grant state, the processor snoops the bus and maintains cache coherency.
Stop-Grant: Similar to G0/S0/C2 state. ICH4 also has the option to assert the CPUSLP# signal to
further reduce processor power consumption.
NOTE: The behavior for this state is slightly different when supporting iA64 processors.
Suspend-To-RAM (STR): The system context is maintained in system DRAM, but power is shut off
to non-critical circuits. Memory is retained, and refreshes continue. All clocks stop except RTC clock.
Suspend-To-Disk (STD): The context of the system is maintained on the disk. All power is then shut
off to the system except for the logic required to resume.
Soft Off (SOFF): System context is not maintained. All power is shut off except for the logic required
to restart. A full boot is required when waking.
Mechanical OFF (MOFF): System context not maintained. All power is shut off except for the RTC.
No “Wake” events are possible, because the system does not have any power. This state occurs if
the user removes the batteries, turns off a mechanical switch, or if the system power supply is at a
level that is insufficient to power the “waking” logic. When system power returns, transition will
depends on the state just prior to the entry to G3 and the AFTERG3 bit in the GEN_PMCON3 register
(D31:F0, offset A4). Refer to Table 5-43 for more details.
Intel^® 82801DB ICH4 Datasheet
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