I’ve been doing some Windows Mobile development with the .NET Compact Framework recently and ran into a scenario where I needed the device to be in “full power” mode at all times with the back-light on. The device is constantly powered, so battery life is not a concern.
The obvious choice is to go into the Brightness and Power control panels and turn off the appropriate settings, but I learned that there is a way to handle this at an application level so the behavior only occurs while the application is running.
An application can force a specific power state using the SetPowerRequirement method, and release that state using the ReleasePowerRequirement method. Using P/Invoke, these methods look like the following:
SetPowerRequirement will allow you to set a specific power state on a specific device. In my scenario, I wanted to set the back-light to full power. The name of the back-light on most (not all) Windows Mobile devices appears to be “BKL1:”. So, to set the back-light to full power (the D0 state), you would call the method as follows:
IntPtr handle = SetPowerRequirement("BKL1:", CEDevicePowerState.D0, 1, IntPtr.Zero, 0);
Lines 1-2 contain the P/Invoke signature. Line 5 sets up a timer that will be called every 10 seconds (10000ms) to reset the idle timer, and lines 7-11 are the timer callback method which actually calls the SystemIdleTimerReset method.
And that’s that. With both of these methods in place, my application remains running with the device at full power, never suspending, and with the back-light always on.