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Device States (D-States)

Device states occur in the global system G0 working state. They were defined to enable device vendors to design ACPI-compliant products, so that operating system that support ACPI, like Windows XP, can manage the devices. There are four D-states, but vendors can choose not to implement all states.

D0 State

  • In this state, the device is operating at its full power and full functionality.
  • Example : A DVD-ROM drive in active use.

D1 State

  • The device can choose to discard its context.
  • However, the bus connected to this device should not do anything to cause the context loss in the device.
  • Power consumption is lower than the D0 state, as some working units in the device will shut down.
  • Example : After idling for some time, the laser in the DVD-ROM drive will automatically turn off, but the drive controller will still be active.

D2 State

  • It is similar to D1, but the bus is free to some power management, like lower the current and voltage.
  • This can save more power, but it will take a longer time to wake up from the D2 state.

D3 State

  • The device in this state can be completely turned off.
  • Maximum power saving is achieved.
  • Wake-up time is the slowest among all D-states.

 

D-State Examples

Example 1 - Hard Disk Drive Power Management Policy

Device State

Required

Power
Consumption

Wake-Up
Latency

Drive
Motor

Drive
Controller

Interface
Context

D0
Yes
100%
0s
on
functional
preserved
D1
Optional
80%
5s
off
functional
preserved
D2
No
n/a
n/a
n/a
n/a
n/a
D3
Yes
10%
6-7s
off
not functional
not preserved

Example 2 - Graphics Card Power Management Policy

Device State

Required

Wake-Up
Latency

Monitor
Display

DPMS

Control
Context

Memory
Content

D0
Yes
0s
on
on
preserved
preserved
D1
Optional
1s
off
on
preserved
preserved
D2
Optional
5s
off
on
lost
lost
D3
Yes
>6s
off
off
lost
lost

* DPMS : Display Power Management Signal, defined by Video Electronics Standard Association (VESA)



<<< Sleeping States (S-States), Sleeping States Summary : Previous Page   |   Next Page : CPU Power States (C-States) >>>

 

 
   
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