Combining Off-line Schedule Construction and Fixed Priority Scheduling in Real-Time Computer Systems

Off-line scheduling and fixed priority scheduling (FPS) are often considered as complementing and incompatible paradigms. A number of industrial applications demand temporal properties (predictability, jitter constraints, end-to-end deadlines, etc.) that are typically achieved by using off-line scheduling. The rigid off-line scheduling schemes used, however, do not provide for flexibility. On the other hand, FPS has been widely studied and used in a number of industrial applications, mostly due to its simple run-time scheduling and small overhead. It provides more flexibility, but is limited with respect to predictability, as actual start and completion times of executions depend on run-time events. In this thesis we first show how off-line scheduling and FPS can be combined to get the advantages of both – the capability to cope with complex timing constraints while providing run-time flexibility. The proposed approach assume that a schedule for a set of tasks with complex constraints has been constructed off-line. We present methods to analyze the off-line schedule and derive FPS attributes such that the runtime FPS execution matches the off-line schedule. In some cases, i.e., when the off-line schedule can not be expressed directly by FPS, we split tasks into instances (artifacts) to obtain a new task set with consistent task attributes. Our method keeps the number of newly generated artifact tasks minimal. At the same time, we investigate the behavior of the existing FPS servers to handle non-periodic events, while the complex constraints imposed on the periodic tasks are still fulfilled. In particular, we pro-