Device Power States (Windows Embedded CE 6.0)
1/6/2010
Device power state definitions are statically predefined. Power Manager passes a device state to a driver, and the driver is responsible for mapping the state to its device capabilities, and then performing the applicable state transition on the device.
The following table describes device power states.
| Device power state | Registry key | Description |
|---|---|---|
Full on |
D0 |
Device is on and running. It is receiving full power from the system and is delivering full functionality to the user. |
Low on |
D1 |
Device is fully functional at a lower power or performance state than D0. D1 is applicable when the device is being used, but peak performance is unnecessary and power is at a premium. |
Standby |
D2 |
Device is partially powered, with automatic wakeup on request. |
Sleep |
D3 |
Device is partially powered, with device-initiated wakeup, if available. A device in state D3 is sleeping but capable of raising the system power state on its own. It consumes only enough power to be able to do so; which must be less than or equal to the amount of power used in state D2. |
Off |
D4 |
Device has no power. A device in state D4 should not be consuming any significant power. Some peripheral busses require static terminations that intrinsically use non-zero power when a device is physically connected to the bus. A device on such a bus can still support D4. |
A physical device does not have to support all of the device power states. The only device power state that all devices must support is the full on state, D0. A driver that is issued a request to enter a power state not supported by its device enters the next available power state supported. For example, if Power Manager requests that it enter D2 and it does not support D2, the device can enter D3 or D4 instead. This can be done if Power Manager supports one of these states. If a device is requested to enter D3 and cannot wake up the system, it should enter D4 and power off, rather than staying in standby. These rules are intended to simplify driver implementation.
Power Manager appropriately maps system power states to the corresponding device power states. For example, if a device only supports device power states D0 and D4, Power Manager does not immediately request that the device enter the D4 power state when it transitions from the full on power state. Power Manager waits until the system enters a system power state in which D3 or D4 is configured as the maximum device power state for that device. If D0, D1, or D2 is configured as the maximum power state, Power Manager keeps the device at D0.
When a device driver is loaded, it should put the device into full on, D0. Before a driver is unloaded, if possible, it should put the device into off, D4. If a device enters another device power state at startup, it can issue a DevicePowerNotify request while processing IOCTL_POWER_CAPABILITIES.
See Also
Reference
Concepts
Power States
Device State D3 and System Wakeup
System Power States