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RTEMS 4.7.2 On-Line Library


Timer Manager Timer Server

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8.2.3: Timer Server

The Timer Server task is responsible for executing the timer service routines associated with all task-based timers. This task executes at a priority higher than any RTEMS application task, and is created non-preemptible, and thus can be viewed logically as the lowest priority interrupt.

By providing a mechanism where timer service routines execute in task rather than interrupt space, the application is allowed a bit more flexibility in what operations a timer service routine can perform. For example, the Timer Server can be configured to have a floating point context in which case it would be save to perform floating point operations from a task-based timer. Most of the time, executing floating point instructions from an interrupt service routine is not considered safe. However, since the Timer Server task is non-preemptible, only directives allowed from an ISR can be called in the timer service routine.

The Timer Server is designed to remain blocked until a task-based timer fires. This reduces the execution overhead of the Timer Server.


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