1 -*- mode: outline -*-

     2 

     3 * ACPI power states.

     4 

     5   http://en.wikipedia.org/wiki/Advanced_Configuration_and_Power_Interface

     6 

     7 ** Global states.

     8 

     9  * G0 (S0) Working

    10  * G1 Sleeping (subdivides into the four states S1 through S4)

    11    * S1: All processor caches are flushed, and the CPU(s) stop executing

    12      instructions. Power to the CPU(s) and RAM is maintained; devices that do

    13      not indicate they must remain on may be powered down.

    14    * S2: CPU powered off.

    15    * S3: Commonly referred to as Standby, Sleep, or Suspend to RAM. RAM

    16      remains powered.

    17    * S4: Hibernation or Suspend to Disk. All content of main memory is saved

    18      to non-volatile memory such as a hard drive, and is powered down.

    19  * G2 (S5) Soft Off. G2, S5, and Soft Off are synonyms. G2 is almost the same

    20    as G3 Mechanical Off, but some components remain powered so the computer

    21    can "wake" from input from the keyboard, clock, modem, LAN, or USB device.

    22  * G3 Mechanical Off: The computer's power consumption approaches close to

    23    zero, to the point that the power cord can be removed and the system is

    24    safe for dis-assembly (typically, only the real-time clock is running off

    25    its own small battery).

    26 

    27 ** System states.

    28 

    29  * S0 Working (G0), Processor in C0-C3, full context save RAM maintained

    30  * S1 Sleeping with processor context maintained, RAM maintained

    31  * S2 Sleeping with processor content not necessarily maintained, RAM

    32    maintained, most devices in D3

    33  * S3 Sleeping, lower than S2, RAM maintained, most devices in D3

    34  * S4 Sleeping, lower than S3, RAM not maintained, most devices in D3

    35  * S5 Sleeping, lower than S4, no context saved, reboot necessary

    36 

    37 ** Device states.

    38 

    39  * D0 Fully-On is the operating state.

    40  * D1 and D2 are intermediate power-states whose definition varies by device.

    41  * D3 Off has the device powered off and unresponsive to its bus.

    42 

    43 ** Processor states.

    44 

    45  * C0 is the operating state.

    46  * C1 (often known as Halt) is a state where the processor is not executing

    47    instructions, but can return to an executing state essentially

    48    instantaneously. All ACPI-conformant processors must support this power state.

    49  * C2 (often known as Stop-Clock) is a state where the processor maintains all

    50    software-visible state, but may take longer to wake up. This processor

    51    state is optional.

    52  * C3 (often known as Sleep) is a state where the processor does not need to

    53    keep its cache coherent, but maintains other state. Some processors have

    54    variations on the C3 state (Deep Sleep, Deeper Sleep, etc.) that differ in

    55    how long it takes to wake the processor. This processor state is optional.

    56 

    57 ** Performance states.

    58 

    59  * P0 max power and frequency.

    60  * P1 less than P0, voltage/frequency scaled.

    61  * Pn less than P(n-1), voltage/frequency scaled.

    62 

    63 * Control power schema under Windows.

    64 

    65 Use powercfg utility. To se current state:

    66 

    67   cmd> powercfg /QUERY

    68 

    69 To see all available states:

    70 

    71   cmd> powercfg /LIST

    72 

    73 To restore power configurtion:

    74 

    75   cmd> powercfg /RestoreDefaultPolicies

    76