Prof. Dr. Reinhard von Hanxleden

"A Multi-Threaded Reactive Processor"

Many embedded systems belong to the class of reactive systems, which continuously react to inputs from the environment by generating corresponding outputs. The programming of reactive systems typically requires the use of non-standard control flow constructs, such as concurrency or exception handling. The synchronous language Esterel has been developed to express reactive control flow patterns in a concise manner, with a clear semantics that imposes deterministic program behavior under all circumstances. However, classical Esterel synthesis approaches suffer from the limitations of traditional processors, with their instruction set architectures geared towards the sequential von-Neumann execution model, or they are very inflexible if HW synthesis is involved.
Recently, another alternative for synthesizing Esterel has emerged, the reactive processing approach. This talk presents a multi-threaded reactive processor, the Kiel Esterel Processor (KEP). The KEP Instruction Set Architecture supports reactive control flow directly, and provides a very dense encoding; code size is typically an order of magnitude smaller than that of the MicroBlaze, a 32-bit COTS RISC processor core. The worst case reaction time is typically improved by 4x, and energy consumption is also typically reduced to a quarter. Apart from efficiency and determinism concerns, another advantage of reactive processors is that due to their comparatively simple structure (no caches, no pipelining) and their direct implementation of the synchronous model of computation it becomes feasible to precisely characterize their timing behavior.