Putting fixed priority scheduling theory into engineering practice for safety critical applications

Describes the approach proposed by the York University Technology Centre for introducing fixed-priority scheduling into industrial safety-critical hard real-time systems. The work has been performed within the context of a class A (safety-critical) system as defined by civil aircraft software standard DO178B. Traditionally, class A systems have been scheduled by a cyclic executive. However, many such systems can be re-designed using a fixed-priority scheduler. This saves time and money, with no significant increase in risk. Also, significant technical benefits are apparent. This paper describes the timing requirements of the system, provides a potential scheduling approach (including appropriate timing analysis), and outlines an approach for gathering the necessary evidence for presentation to certification authorities.