An optimal number of microprocessor units with watchdog processor

A large number of microprocessors (μPs) have been widely used in many practical fields. A watchdog processor (WDP) is the most convenient coprocessor to monitor the behavior of a μP since it is simple and low-priced. This paper considers a system with N μP units, where each μP unit consists of μP and WDP. When errors of a μP have occurred, a WDP detects them and resets a μP to an initial state. The reset number is checked at constant time T. If more than K resets have been made at time T, a μP becomes permanently faulty and one of other μP units in standby begins to operate. The mean time and the expected cost until system failure are derived. An optimal number N∗ which minimizes the expected cost is discussed.