The Power Manager expects all managed devices to support one or more device power states. There are a limited number of device power states, and the device must inform the Power Manager of their power consumption characteristics. Device power states generally trade off performance with power consumption.
The Power Manager manages device power states within the context of system power states that are defined by the OEM. System power states are described in the registry and any number can be defined. System power states impose an upper bound on device power states.
Some applications may require that a given device be maintained at a certain device power level. For example, a streaming audio application might require that its network card and audio codec stay powered at a high level while music is playing. A streaming video application might need network and audio, plus it might want to keep the display from going into screen saver mode and possibly keep the backlight on. Applications can request that the Power Manager set minimum device power state requirements using the SetPowerRequirement and ReleasePowerRequirement APIs.
Last updated on Tuesday, May 18, 2004
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