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1 .. -*- coding: utf-8; -*- |
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2 .. include:: HEADER.rst |
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3 |
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4 ================== |
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5 Power management |
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6 ================== |
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7 |
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8 * ACPI power states. |
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9 |
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10 http://en.wikipedia.org/wiki/Advanced_Configuration_and_Power_Interface |
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11 |
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12 ** Global states. |
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13 |
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14 * G0 (S0) Working |
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15 * G1 Sleeping (subdivides into the four states S1 through S4) |
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16 |
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17 * S1: All processor caches are flushed, and the CPU(s) stop executing |
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18 instructions. Power to the CPU(s) and RAM is maintained; devices that do |
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19 not indicate they must remain on may be powered down. |
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20 * S2: CPU powered off. |
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21 * S3: Commonly referred to as Standby, Sleep, or Suspend to RAM. RAM |
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22 remains powered. |
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23 * S4: Hibernation or Suspend to Disk. All content of main memory is saved |
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24 to non-volatile memory such as a hard drive, and is powered down. |
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25 * G2 (S5) Soft Off. G2, S5, and Soft Off are synonyms. G2 is almost the same |
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26 as G3 Mechanical Off, but some components remain powered so the computer |
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27 can "wake" from input from the keyboard, clock, modem, LAN, or USB device. |
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28 * G3 Mechanical Off: The computer's power consumption approaches close to |
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29 zero, to the point that the power cord can be removed and the system is |
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30 safe for dis-assembly (typically, only the real-time clock is running off |
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31 its own small battery). |
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32 |
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33 ** System states. |
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34 |
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35 * S0 Working (G0), Processor in C0-C3, full context save RAM maintained |
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36 * S1 Sleeping with processor context maintained, RAM maintained |
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37 * S2 Sleeping with processor content not necessarily maintained, RAM |
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38 maintained, most devices in D3 |
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39 * S3 Sleeping, lower than S2, RAM maintained, most devices in D3 |
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40 * S4 Sleeping, lower than S3, RAM not maintained, most devices in D3 |
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41 * S5 Sleeping, lower than S4, no context saved, reboot necessary |
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42 |
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43 ** Device states. |
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44 |
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45 * D0 Fully-On is the operating state. |
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46 * D1 and D2 are intermediate power-states whose definition varies by device. |
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47 * D3 Off has the device powered off and unresponsive to its bus. |
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48 |
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49 ** Processor states. |
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50 |
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51 * C0 is the operating state. |
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52 * C1 (often known as Halt) is a state where the processor is not executing |
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53 instructions, but can return to an executing state essentially |
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54 instantaneously. All ACPI-conformant processors must support this power state. |
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55 * C2 (often known as Stop-Clock) is a state where the processor maintains all |
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56 software-visible state, but may take longer to wake up. This processor |
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57 state is optional. |
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58 * C3 (often known as Sleep) is a state where the processor does not need to |
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59 keep its cache coherent, but maintains other state. Some processors have |
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60 variations on the C3 state (Deep Sleep, Deeper Sleep, etc.) that differ in |
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61 how long it takes to wake the processor. This processor state is optional. |
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62 |
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63 ** Performance states. |
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64 |
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65 * P0 max power and frequency. |
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66 * P1 less than P0, voltage/frequency scaled. |
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67 * Pn less than P(n-1), voltage/frequency scaled. |
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68 |
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69 * Control power schema under Windows. |
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70 |
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71 Use powercfg utility. To se current state: |
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72 |
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73 cmd> powercfg /QUERY |
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74 |
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75 To see all available states: |
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76 |
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77 cmd> powercfg /LIST |
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78 |
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79 To restore power configurtion: |
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80 |
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81 cmd> powercfg /RestoreDefaultPolicies |
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82 |
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83 * Intel. |
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84 |
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85 ** Intel Speedstep® Technology. |
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86 |
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87 http://www.intel.com/support/processors/sb/CS-028855.htm |
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88 Frequently asked questions for Intel Speedstep® Technology |
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89 http://www.intel.com/p/en_US/support/highlights/processors/frequencyid |
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90 Intel® Processor Frequency ID Utility |
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91 http://software.intel.com/en-us/articles/enhanced-intel-speedstepr-technology-and-demand-based-switching-on-linux |
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92 Enhanced Intel SpeedStep® Technology and Demand-Based Switching on Linux |