The setup and verification of time-triggered communication systems are very tedious. Detailed process time information like the Worst Case Execution Time (WCET) must be gathered beforehand to determine the slot sizes such that no slot violations occur. For highly dynamical systems like prototypes, the investigation of the WCETs and thus the setup is very costly. Here, mostly the code is modified which influences the process execution time.
In this paper, we present two mechanisms, which provide additional information about the time-triggered bus communication state during run-time. The gathered information is used to identify tight slot boundaries which simplifies the setup and verification of such a system.
As a prerequisite, we assume that the predefined schedule is imprecise due to missing process time information. Therefore, our first mechanism is applied to detect slot violations. At the beginning of each slot, the participants check if the previous message already arrived. If this is not the case, a slot violation occurred and the current task’s execution is delayed until the expected message is received. With this, message collisions are prevented and the entire communication system is kept alive.
The second mechanism is applied to gather detailed information during run-time which is used to rate various slot specific qualities. Thereby, the bus communication is analyzed by tracking the message reception times. The gathered data is compared to the known slot boundaries and the quality ratings are determined. As a result, the additional information enables an implicit verification of the communication state which can further be used for an extended node control.
We claim, that the gathered information will reduce the effort to set up and verify a time-triggered bus communication in highly flexible systems. The feasibility and performance of the presented mechanisms are currently investigated and will be presented in a follow-up paper.
S. Einspieler, B. Steinwender, W. Elmenreich. Integrating Time-Triggered and Event-Triggered Communication in a Hard Real-Time System. In Proceedings of the 1st IEEE International Conference on Industrial Cyber-Physical Systems (ICPS 2018), St. Petersburg, Russia, May 2018.