A formal specification of the RT-Middleware data transfer protocol

Abstract

The RT-Middleware framework, which is used on both robotic and non-robotic systems in Japan, uses “DataPorts” to provide one-way, flow-based data communication. These ports are built upon a custom protocol which is in turn built on top of a Remote Procedure Call mechanism and a set of data buffers. The protocol is used to transfer data according to a set of communication policies specified by a system integrator. It forms the major foundation of systems built in the framework. Therefore, in order to have confidence in systems built using RT-Middleware we require confidence that this protocol is correct and will transfer the data to destinations as expected. This paper describes a formal specification of the RT-Middleware DataPort protocol, and verification of the correctness of this specification. The specification is written using the TLA+ formal specification language, and verification is performed using model checking. We describe the specification itself and present an example of the model-checking. We demonstrate that the protocol behaves as described in its informal specification, absent external errors. The presence of a formal specification increases confidence in the correctness of the software, and also provides an unambiguous description of expected behaviour when creating additional implementations.