From running code to event-graphs: a pragmatic approach to derive WCRT of protocol compositions

A flexible way of building modular communication stacks relies on the use of protocol composition. In order to derive the worst-case response time of a protocol composition, one needs to capture its event-graph: the event-graph consists of the set of all events processed by each component and how these events are related. This paper describes a protocol composition framework that simplifies the task of deriving the event-graph from the protocol implementation. The framework, called RT-Appia, takes a pragmatic approach: instead of requiring the use of domain specific code analysis tools, or dedicated compilers, it simply requires protocol programmers to make explicit which events are processed and produced by each layer, and how these events are related. The interest of the approach is that the same data structures are used not only to simplify the task of computing the worst case response time of the protocol composition, but also to optimize the performance and for debugging the resulting implementation.