Non-preemptive interrupt scheduling for safe reuse of legacy drivers in real-time systems

Low-level support of peripheral devices is one of the most demanding activities in a real-time operating system. In fact, the rapid development of new interface boards causes a tremendous effort at the operating system level for writing and testing low-level drivers for supporting the new hardware. The possibility of reusing legacy drivers in real-time systems would offer the great advantage of keeping the rate of changes with a small programming effort. Since typical legacy drivers are written to execute in a non-preemptive fashion, a suitable operating system mechanism is needed to protect real-time application tasks from unpredictable bursty interrupt requests. In this paper we present a novel approach suitable for scheduling interrupt service routines. Main features of the method include: high priority of the handler non preemptive execution, bandwidth reservation for the application tasks, and independence of the interrupt service policy from the scheduling policy adopted for the application tasks.