This paper describes our work towards a rapid prototyping system for hard real-time systems focusing on scheduling algorithms and scheduler implementations. The framework aims at speeding up the decision making process during selection of a suitable scheduling algorithm for a real-time application. The framework supports various kinds of realtime scheduling algorithms, which can be simulated for evaluation purposes. Furthermore, implementations of these algorithms can be tested in a real-time operating system (RTOS) with real or synthetic workloads. The algorithms are implemented as software routines, which are part of the operating system (OS), or realized within a coprocessor to free the operating system kernel from time consuming scheduling operations. Both kinds of implementations have to provide an application programmers interface that hides the algorithm from implementation issues. The target operating system of our framework is mainly RTLinux, eventhough development for those systems is possible under Linux as well as Windows-NT. The framework proposed in this paper is new in that it supports the selection of the right algorithm and the right implementation for the target platform based on real-time scheduling analysis. 1

Scheduling time impact on system performance increases especially when using dynamic priority algorithms, because of the enlarged computational effort at runtime. This overhead can be reduced by using dedicated hardware that does the time consuming computations necessary for scheduling. This can be a coprocessor capable of implementing dynamic scheduling algorithms which are, until now, rarely used because of their complex computations at schedule time. One of these algorithms is Least-Laxity-First (LLF). This is an optimal scheduling methodology that allows detection of time constraint violations ahead of reaching a tasks deadline, but has the disadvantage of showing poor runtime behavior in some special situations (“thrashing”). In this paper, we present a universal deterministic scheduling coprocessor that implements the newly developed Enhanced Least-Laxity-First-algorithm (ELLF) which eliminates this disadvantage of LLF. Computation time of this device is rather a matter of time resolution than of the number of tasks. 1.