Back to the Roots: Implementing the RTOS as a Specialized State Machine

Abstract — Real-time control systems, originally arisen from simple, state-machine–based discrete elements, nowadays com-prise sophisticated and manifold software-based algorithms con-solidated with different applications on single, yet powerful microcontrollers. Real-time operating systems were introduced to handle this complexity by providing APIs to describe the desired system behavior, however, at the cost of losing the clarity and explicitness of state-machine–based representations. This paper presents an approach to bring the RTOS back to the roots of a hardware-implementable finite state machine. The con-cept is based on a detailed static analysis of the application–kernel interaction to distill the real-time operating system behavior and find a FSM-based representation of the expected OS states and transitions. We apply our idea to a realistic control application based on an OSEK operating system, which results in a feasibly sized programmable logic array implementation. Having such a representation at hand might further leverage thorough system verification and validation based on existing and mature FSM analysis tools. I