Description
Relay Ladder Logic (RLL) is a programming language widely used for complex embedded control applications such as manufacturing and amusement park rides. The cost of bugs in RLL programs is extremely high, often measured in millions of dollars (for shutting down a factory) or human safety (for rides). In this paper, we describe our experience in applying constraint-based program analysis techniques to analyze production RLL programs. We demonstrate that our analyses are useful in detecting some common programming mistakes and can be easily extended to perform other kinds of analysis for RLL programs such as some of the analyses described in Barrett's Ladder Logic Analysis Survey.