Model-Based Generation of Interlocking Controller Software from Control Tables

Railroad interlocking software drives specialised micro-devices, known as interlocking controllers. These controllers primarily actuate railroad points and change signal aspects in real-time, based on sensor and timer input. Due to their central function in railroad control, interlocking controllers and their firmware are safety-critical. The firmware programs, which mimic physical relays, are written in variants of domain-specific programming languages based on ladder logic. The programs have to comply with a more abstract specification of allowable states of sections of railroad track and equipment, known as a control table. The translation of a track layout and associated control tables into ladder logic-based code is manual, and hence subject to costly review and rework cycles. In this report, we describe a case study that uses a model-driven tool-chain as an automated alternative to the existing process. The two domain languages, control table and ladder logic, were modelled and transformations were implemented between the two models, and from model to program text. We report on implementation challenges, and describe the outlook and scalability of the approach in this application domain.