An Operating System for a Time-Predictable Computing Node

Abstract. The increasing complexity of speed-up mechanisms found in modern computer architectures makes it difficult to predict the timing of the software that runs on this hardware, especially when the soft-ware itself has many different execution paths. To fight this combined hardware-software complexity that makes an accurate timing analysis in-feasible, we have conceived a very simple software structure for real-time tasks: We do not allow that decisions about the control flow are made at runtime, i.e., all decisions are resolved in an off-line analysis before runtime. In this paper we show that simple control structures generated before runtime can as well be used within the operating system of an embedded real-time system. In this way we make not only task timing but also the timing of the operating system and thus the timing of the entire real-time computer system fully deterministic, thus time-predictable. We explain the principles and mechanisms we use to achieve this predictability and show the results of an experiment that demonstrates the feasibility of our concepts