Safety-critical systems built with COTS

Abstract

In the rail transportation industry competitive pressure has led to the increased use of COTS (commercial off-the-shelf equipment in safety critical systems), making it imperative that we extend proven safety techniques to COTS based systems as well. To this end, we have developed the Vital Framework (V-Frame), which is used to develop a safety critical platform from COTS hardware and software. The key technologies in this framework are formal methods, information redundancy, a proprietary data format, and a concurrent checking scheme. Combining these technologies results in a real time, checkable correctness criterion that is a signature of the application's algorithm structure and is independent of both the hardware and the operating system. V-Frame's most significant attribute is that the fail safe properties of applications do not require the firmware to be correct: the application will operate in a fail safe (or vital) manner even if there are design faults in the operating system and/or the hardware fails. This does not mean that the application does not have to be correctly specified and designed. Formal methods are appropriate in the design of safety critical COTS systems because a generic processing environment is analogous to a formal system: it is designed to apply well defined transformation rules to inputs.