Influence of software on fault-tolerant microprocessor control system dependability

The fault tolerance of the control system in this paper is based on cold standby and software redundancy. The control system is a microprocessor modular system. It consists of standard nonredundant modules and specific additional modules. The fault-tolerant control system performs the validation of the active microprocessor unit and the actualization of the spare unit. In the case of the active unit failure, the control from the failed active unit is switched to the spare unit. The fault detection is based on a watchdog timer, checksums, data duplication, etc. The evaluation of the fault tolerance of this control system is performed by fault injection into the active unit bus lines performed by a fault injection system that records the tested system reaction. The control system is tested for nonredundant and redundant software. The influence of the watchdog period and actualization of standby unit period on the number of detected faults in the active and the standby unit is observed. This experimental method is therefore one of the ways to compare the quality of some fault-tolerant methods. The fault tolerance of the control system could be easily increased by using software redundancy and software methods.