Mode changes in priority preemptively scheduled systems

It is noted that in many hard real-time systems, the set of functions that a system is required to provide may change over time. One way of providing this change is to allow currently running hard real-time tasks to be deleted or changed, or new tasks to be added. The authors define this change as a mode change, and seek to guarantee a priori the timing constraints of all tasks across the change from one mode to another. The authors derive a scheduling theory for static priority preemptive scheduling that can be used to make such guarantees. The schedulability test discussed could easily be incorporated into engineering support tools. The authors also discuss some of the approaches that could be taken to extend the analysis to cope with more complex and interesting scheduling problems, and to handle distributed hard real-time systems