Types of System Tick Timers (Windows CE 5.0)
In general, hardware platforms provide one of the following types of timers:
- Fixed interval timers that cannot be reprogrammed. These interrupt the system at a fixed rate and cannot be updated once they are started. CEPC uses this kind of timer. Fixed interval timers should be avoided in mobile battery-powered systems as there is no way for the kernel to conserve power with OEMIdle.
- Programmable interval timers (PITs) automatically count down to zero, generate an interrupt, and automatically reload and start over. Most SHx-based hardware platforms use this kind of timer.
- Free-running counters with value and compare registers count up or down until the value register equals the match register, at which point they generate an interrupt. Even after the interrupt, the value register keeps counting. To generate another interrupt, the match register must be reprogrammed. XScale and DDB5476 hardware platforms use this kind of timer.
Fixed-rate timers limit the functionality of OEMIdle and the thread timer to conserve power. For more information, see Boilerplate Interface Routines.
See Also
Sample OAL Implementations of OEMIdle
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