Coloured Petri Net Modelling of Real-Time Task Scheduling

Embedded computers are widely used to perform functions with real-time constraints. Such real-time computer systems typically use separate tasks for implementing independent functions, requiring a run-time system to schedule tasks for execution. Confirming that tasks satisfy their real-time constraints is possible using schedulability analysis for single processor systems where system design has been suitably constrained. However, where system design uses complex inter-task interactions, or asynchronous task arrival times, or multiple processors, it becomes difficult to verify that tasks will satisfy real-time constraints. A generic coloured petri net model has been developed to support analysis of the run-time behaviour of real-time systems. The model accommodates multiprocessor architectures with tasks statically bound to processors, and without restrictions on inter-task communications. First application of the model has been to the mission computers of a Seahawk helicopter, to test model applicability to a complex multiprocessor system. The model was successfully used to verify real-time constraints on task executions for system operation in a single scenario. Inherently high complexities associated with scheduling problems remain a challenge to successful modelling, and there is a risk of modelling being computationally infeasible for some systems