Methodology for priority assignment under backward-compatibility constraints

This invention describes a methodology to build a schedule for a priority-based real-time system, which is feasible / schedulable, is backward-compatible to the given schedule, and is extensible towards future modifications. A set of old frames is input to the system and retain their priority. For each frame in a set of new frames with unassigned priorities a temporary priority is assigned having a priority higher than any old frame. A set of unassigned frames are then allocated to a new set and the next free priority level is identified. An unassigned frame is assigned to the free priority level and a determination is made whether the allocation is feasible. If acceptable the frame is allocated until the set of unassigned frames is empty. If the allocation is not feasible the next higher priority is used. The process is repeated until all frames have been allocated. In a second embodiment a threshold value based on the response time and deadline may be used to allocate the priority.