The digraph real-time task model

Models for real-time systems have to balance the inherently contradicting goals of expressiveness and analysis efficiency. Current task models with tractable feasibility tests have limited expressiveness, restricting their ability to model many systems accurately. In particular, they are all recurrent, preventing the modeling of structures like mode switches, local loops, etc. In this paper, we advance the state-of-the-art with a model that is free from these constraints. Our proposed task model is based on arbitrary directed graphs (digraphs) for job releases. We show that the feasibility problem on preemptive uniprocessors for our model remains tractable. This even holds in the case of task systems with arbitrary deadlines.