Software Issues In Redundant Sequential Control

Redundant control systems require more than a single redundant construct to serve the six basic functions of fault tolerance: test, detection, diagnosis, masking, reconfiguration, and recovery. Software usually constitutes or supports one or more such constructs. Additionally, software must be correct, since it is seldom, if ever, protected by redundancy. A redundant sequential control system requires intricate software constructs. The predominant existing software specification and implementation techniques for sequential control are not adequate for the creation of correct software of the complexity required for redundant systems. This complexity is illustrated by an example.