ACPI(Advanced Configuration and Power Interface) 상태 정의

 

1. Global states

 

The ACPI specification defines the following seven states (so-called global states) for an ACPI-compliant computer-system:

• G0 (S0) Working
• G1 Sleeping (subdivides into the four states S1 through S4)
  • S1: All processor caches are flushed, and the CPU(s) stop executing instructions. Power to the CPU(s) and RAM is maintained; devices that do not indicate they must remain on may be powered down.
  • S2: CPU powered off
  • S3: Commonly referred to as Standby, Sleep, or Suspend to RAM. RAM remains powered
  • S4: Hibernation or Suspend to disk. All content of main memory is saved to non-volatile memory such as a hard drive, and is powered down.
• G2 (S5) Soft Off. G2, S5, and Soft Off are synonyms. G2 is almost the same as G3 Mechanical Off, but some components remain powered so the computer can "wake" from input from the keyboard, clock, modem, LAN, or USB device.
• G3 Mechanical Off: The computer's power consumption approaches close to zero, to the point that the power cord can be removed and the system is safe for dis-assembly (typically, only the real-time clock is running off its own small battery).

Furthermore, the specification defines a Legacy state: the state when an operating system runs which does not support ACPI. In this state, the hardware and power are not managed via ACPI, effectively disabling ACPI.

State	Description
S0/Working	System is on. The CPU is fully up and running; power conservation operates on a per-device basis.
S1 Sleep	System appears off. The CPU is stopped; RAM is refreshed; the system runs in a low power mode.
S2 Sleep	System appears off. The CPU has no power; RAM is refreshed; the system uses a lower power mode than S1.
S3 Sleep (Standby)	System appears off. The CPU has no power; RAM is in slow refresh; the power supply is in a reduced power mode. This mode is also referred to as 'Save To RAM'.
S4 Hibernate	System appears off. The hardware is completely off, but system memory has been saved as a temporary file onto the harddisk. This mode is also referred to as 'Save To Disk'.
S5/Off	System is off. The hardware is completely off, the operating system has shut down; nothing has been saved. Requires a complete reboot to return to the Working state.
Source	http://www.lifsoft.com/power/faq.htm

 

2. System states

• S0 Working (G0), Processor in C0-C3, full context save RAM maintained
• S1 Sleeping with processor context maintained, RAM maintained
• S2 Sleeping with processor content not necessarily maintained, RAM maintained, most devices in D3
• S3 Sleeping, lower than S2, RAM maintained, most devices in D3
• S4 Sleeping, lower than S3, RAM not maintained, most devices in D3
• S5 Sleeping, lower than S4, no context saved, reboot necessary

 

3. Device states

The device states D0-D3 are device-dependent:

• D0 Fully-On is the operating state.
• D1 and D2 are intermediate power-states whose definition varies by device.
• D3 Off has the device powered off and unresponsive to its bus.

 

4. Processor states

The CPU power states C0-C3 are defined as follows:

• C0 is the operating state.
• C1 (often known as Halt) is a state where the processor is not executing instructions, but can return to an executing state essentially instantaneously. Some processors, such as the Pentium 4, also support an Enhanced C1 state (C1E) for lower power consumption, all processors must support this power state.
• C2 (often known as Stop-Clock) is a state where the processor maintains all software-visible state, but may take longer to wake up, this processor state is optionally supported by the system.
• C3 (often known as Sleep) is a state where the processor does not need to keep its cache coherent, but maintains other state. Some processors have variations on the C3 state (Deep Sleep, Deeper Sleep, etc.) that differ in how long it takes to wake the processor. This processor state is optionally supported by the system.

 

5. Performance states

While a device or processor operates (D0 and C0, respectively), it can be in one of several power-performance states. These states are implementation-dependent, but P0 is always the highest-performance state, with P1 to Pn being successively lower-performance states, up to an implementation-specific limit of n no greater than 16.

P-states have become known as SpeedStep in Intel processors, as PowerNow! or Cool'n'Quiet in AMD processors, and as PowerSaver in VIA processors.

• P0 max power and frequency
• P1 less than P0, voltage/frequency scaled
• Pn less than P(n-1), voltage/frequency scaled

 

출처: From Wikipedia, Advanced Configuration and Power Interface