An Operating System for a Time-Predictable Computing Node

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 software itself has many different execution paths. To fight this combined hardware-software complexity that makes an accurate timing analysis infeasible, 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.