Activity Timer Events (Windows CE 5.0)
You can set activity timer events in a device driver without overloading the CPU. The Power Manager does not wait for the timer reset event while it waits for the timer to expire. After the activity timer time-out, Power Manager checks to see if the reset event was set during the interim. If the reset event has not been set, the timer is considered to have expired. If a reset event has been set, the Power Manager resets the time-out and once again waits for the timer. The Power Manager only updates the manual reset timer events when the timer has expired with the reset event not signaled, or when the reset event is signaled for the first time after a period of inactivity.
The activity timer thread of the Power Manager does not run if a driver thread runs at a higher priority. This is true even if the Power Manager is actively waiting on the timer reset event. By default, the activity timer thread runs at a level of THREAD_PRIORITY_ABOVE_NORMAL, while a majority of drivers run at THREAD_PRIORITY_HIGHEST or above. This causes the activity timer thread to not preempt the driver.
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