Diagnosis of a congestion problem of tasks in a real-time system

Abstract

In this paper, we study the problem of accumulated tokens in a timed Petri net modeling our system and its interaction with the environment. This system consists of a robot, a programmable automaton and a computer. The execution of different tasks must be done with respect to some temporal constraints. So, we use the temporal Petri nets to model the whole system and also its verification. We describe the obtained Petri net and the constraints textually or graphically in the open source TINA environment. The studied problem is a consequence of a wrong functioning. We try two approaches to solve it: the first one is behavioral-like, it makes a review of tasks scheduling, it is based on the priorities granting to specific transitions in order to fire some transitions before others; while the second one is structural-like, and it introduces some changes to the net structure with respect of the specification of the system. The obtained results show that the problem of accumulated tokens in a Petri net is not deeply related to a scheduling problem, but it is a structural problem. These two approaches can be combined into a hybrid one. These testing results also serve for the re-design process of the system by reviewing the problem sources.