Middleware for Cyber-Physical Systems

One of the objectives of CyPhyAssure is to enable compositional modular assurance for autonomous robots. In order to decompose and apportion safety requirements to different subsystems or constituents, it is necessary to consider the architecture of the robot. In particular, we need to consider the paradigm of the underlying middleware in order to compose the execution semantics of the different components.

One of the most popular middlewares for robots seems to be ROS, the “Robot Operating System”. Actually, ROS is not an operating system, but a middleware that sits on top of an operating system like Linux. One of the core components of ROS is its communication infrastructure, which provides a publish-subscribe protocol, where constituents advertise their services using “topics”, which other components can subscribe and listen to. In order to support robotic systems with real-time constraints, the new ROS 2.0, which is currently under development, will support a publish-subscribe middleware called DDS (Data Distribution Service).

An alternative approach to the publish-subscribe protocol, is the PALS architecture, which stands for “Physically Asynchronous Logically Synchronous”. PALS recognises the underlying asynchrony in a communication medium, but employs a pattern that allows the system design to be synchronous in nature, which in particular makes it more amenable to formal verification.