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 – S-Method, which 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 additional timer update overhead, such as deletion and insertion for new timeout. Experiments show that this method can reduce the time of timer update and increase stability and predictability in timer update time.