Scheduling Aperiodic and Sporadic Tasks in Hard Real - Time Systems

The stringent timing constraints as well as the functional correctness are essential requirements of hard real-time systems. In such systems, scheduling plays a very important role in satisfying these constraints. The priority based scheduling schemes have been used commonly due to the simplicity of the scheduling algorithm. However, in the presence of task interdependencies and complex timing constraints, such scheduling schemes may not be appropriate due to the lack of an e cient mechanism to schedule them and to carry out the schedulability analysis. In contrast, the time based scheduling scheme may be used to schedule a set of tasks with greater degree of schedulability achieved at a cost of higher complexity of o -line scheduling. One of the drawbacks of currently available scheduling schemes, however, is known to be their in exibility in dynamic environments where dynamic processes exist, such as aperiodic and sporadic processes. We develop and analyze scheduling schemes which e ciently provide the exibility required in real-time systems for scheduling processes arriving dynamically. This enables static hard periodic processes and dynamic processes(aperiodic or sporadic) to be jointly scheduled. This work is supported in part by ONR and ARPA under contract N66001-95-C-8619 to the Computer Science Department at the University of Maryland. The views, opinions, and/or ndings contained in this report are those of the author(s) and should not be interpreted as representing the o cial policies, either expressed or implied, of the Advanced Research Projects Agency, ONR or the U.S. Government.