A Proposal of Fault Tree Analysis for Embedded Control Software

Abstract

There are many industrial products in our life, and the actions of those products are controlled by embedded control software (ECSW). Recently, many troubles have been caused by ECSW. To avoid those troubles, it is necessary to clarify the causes of the troubles and take countermeasures. However, the results of those tasks depend on the skills of the analyst. This paper proposes an analytic method that clarifies the causes of troubles by applying fault tree analysis (FTA) to the ECSW. The characteristics of the proposed method are as follows: Preparation of fault tree templates (FTTs) corresponding to instructions of the ECSW, and definition of the FT development rules by combining FTTs according to the back-tracing of the instruction execution process. By complying with the proposed method strictly, when an analyst who has studied computer science and safety engineering for 2–3 years conducts FTA, the analyst can obtain an appropriate result of FTA. This indicates that the safety level of ECSW will improve. As a result of applying the proposed method to existing ECSWs, we find that we can obtain the result of FTA at the appropriate level.