I have a device driver that uses another device driver. How do I create a hierarchy of power requirements?
An example of this might be an Infrared Data Association (IrDA) driver that depends on a COM port driver. Unfortunately there is no mechanism for this in either Windows CE .NET or in Windows CE .NET v4.1, because the dependency of one device driver on another is not propagated through the operating system. Also, device drivers don’t know anything about requirements that may have been imposed on them by applications—only the Power Manager knows about requirements. One way to do this would be customize the Power Manager to support an optional DependsOn registry key associated with each device. Assume that the IrDA interface is COM5: and it depends on a serial port interface called COM2:. When an application calls SetPowerRequirement() on COM5:, the Power Manager can look in the registry and impose an appropriate matching requirement on COM2:. Alternatively, the COM2: driver could simply not advertise its interface with the Power Manager directly. When the IrDA driver at COM5: starts up,
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