What is the relationship between the Power Manager and the system of power callbacks that Windows CE has always used?
The goal of the Power Manager is to enable intelligent management of device power. Within the Power Manager framework, OEMs define system power states that establish maximum device power states, devices call DevicePowerNotify() to regulate their own power levels, and applications call SetPowerRequirement() to make sure that the devices they need are running at a performance level that suits their needs. The power callbacks (that is, xxx_PowerDown()/xxx_PowerUp()) are independent of the power manager. These callbacks occur when the system is about to enter a suspend mode in which the CPU is stopped. They are generated immediately before OEMPowerOff() is invoked. Device drivers will often receive IOCTLs prior to the system suspend that request them to turn themselves off, but this is not always the case. The Power Manager framework allows devices to be turned off while the system is running or left on while the system is suspended. It is up to device driver implementers to decide what to
