Research on the Schedulability of Sporadic Tasks in Spaceborne Mixed Real-Time Operating System

A spacecraft is a typical time-sensitive system, and the characteristics of hard real-time and limited resources make the design of real-time scheduling algorithms particularly crucial in spaceborne operating system. With the development of space technology, onboard computer has transformed from a closed system with a single type of task to an open system with mixed sets of tasks. The system allows new tasks to be dynamically loaded during operation, leading to real-time changes in the types and numbers of tasks, further increasing the difficulty of predicting and the uncertainty of the system. Sporadic tasks are more common in actual system and have special temporal characteristics of releasing by a random frequency, making the schedulability determination more complex than that of other types of tasks. Therefore, we focused on the schedulability of sporadic tasks in spaceborne operating system and first classified the situations in which schedulability needs to be determined. For each preemption case in different situations, corresponding determination strategies were proposed based on Response Time Analysis (RTA). Due to RTA’s high time complexity, we additionally utilized Interference Bound Function (IBF) to judge the schedulability, thus providing flexible choices for system design. By tracking task’s runtime information and analyzing at a finer granularity, our methods reduced pessimism and achieved a better schedulable ratio.