A New Implementation Method of Timer for Periodic Tasks

In real-time systems, an efficient and stable implementation of timer is crucial to the timing requirements of tasks. The traditional methods take O(n²) time overhead to maintain timers in the periodic task model. In this paper, we present a new implementation method that takes O(n) time overhead. This method calculates all trigger instants of periodic tasks within a hyperperiod off-line, and assigns these instants to corresponding periodic timers. The timer system checks whether a trigger instant arrives in the timer Interrupt Service Routine (ISR), and activates tasks periodically without any additional overhead, such as deletion and insertion for new timeouts. Experiments show that the method presented in this paper can improve the execution speed of timers with low overhead in space and increase stability in execution time.