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Real-Time Concepts for Embedded SystemsChapter 11: Timer and Timer Services 11.1 Introduction In embedded systems, system tasks and user tasks often schedule and perform activities after some time has elapsed. For example, a RTOS scheduler must perform a context switch of a preset time interval periodically-among tasks of equal priorities-to ensure execution fairness when conducting a round-robin scheduling algorithm. A software-based memory refresh mechanism must refresh the dynamic memory every so often or data loss will occur. In embedded networking devices, various communication protocols schedule activities for data retransmission and protocol recovery. The target monitor software sends system information to the host-based analysis tool periodically to provide system-timing diagrams for visualization and debugging. In any case, embedded applications need to schedule future events. Scheduling future activities is accomplished through timers using timer services. Timers are an integral part of many real-time embedded systems. A timer is the scheduling of an event according to a predefined time value in the future, similar to setting an alarm clock ...» |
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