Controlling large cyclic avionics software systems written in Ada

Although Ada was created to standardize programming for real-time embedded computer applications, especially in defense systems, it has inherent limitations when applied to large numbers of concurrent periodic processes. Modern integrated avionics systems, such as are in use on the AGUSTA A-129 Mangusta Helicopter, involve as many as 140 concurrent periodic tasks running at a variety of frequencies from 180 Hz to once every 30 seconds. Published Ada solutions to managing concurrent periodic tasks revert to a 1960´s `cyclic executive´ technology, thrust control logic into the applications code, or introduce significant system overhead. When software systems get very large and involve tasks of varying duration and execution frequencies, these solutions become unmanageable. The problem domain and several of these approaches are outlined, and the alternate solutions are presented. Central to the issue is the preservation of determinism in the execution control of integrated avionics software systems