Debugging Parallel DEVS

To this day, debugging support for the DEVS formalism has been provided, at best, in an ad-hoc way. The intricacies of dealing with the interplay of different notions of (simulated) time, the formalism semantics, and user input, has not been thoroughly investigated. This paper presents a visual modelling, simulation, and debugging environment for Parallel DEVS, which builds on a theoretical foundation for debugging DEVS models. We take inspiration from both the code debugging and the simulation world to model our environment; we transpose a set of useful code debugging concepts onto Parallel DEVS, and combine those with simulation-specific operations, such as as-fast-as-possible simulation and (scaled) real-time execution. Apart from these common debugging operations, we introduce new features to the debugging of Parallel DEVS models, such as “god events”, which can alter the model state during simulation, and reversible debugging, which allows to go back in time. To achieve this, the PythonPDEVS simulator is deand reconstructed: the modal part of the simulator/debugger, as well as the debugging operations, are modelled using the Statecharts formalism. These models are combined, resulting in a model of the timed, reactive behaviour of a debuggable simulator for Parallel DEVS. The code for the simulator is automatically synthesized from this model. To improve usability, we combine the simulator with a visual modelling environment, allowing for visual and interactive live debugging.