State Machine of a Redundant Computing Unit Operating as a Cyber-Physical System Control Node with Hot-Standby Redundancy

Cyber-physical systems CPS are computer systems interconnected with physical world. In case of industrial applications they are called also Industrial Control Systems ICS. Most characteristic feature of ICS is operation in real-time. It means that they must satisfy strictly defined temporal constraints. Another important aspect is reliability. It is expected that ICS system operates 24/7. Some systems have to be also fault-tolerant, which means that a failure of one or more components should not disable proper operation of the system. To satisfy the latter demand, redundancy is used. One of examples of redundancy application is redundancy of computing units (like for example Programmable Logic Controllers PLCs in industrial control systems). It may be realized using dedicated components but also in more cost-effective way, using standard elements. In the second case, proper implementation of software redundancy routines is crucial. The paper shows a state machine used for implementation of computing units redundancy operating in hot-standby mode.