A complex real-time embedded system may consist of multiple application components each of which has its own timeliness requirements and is scheduled by component-specific schedulers. At run-time, the schedules of the components are integrated to produce a system-level schedule of jobs to be executed. We formalize the notions of schedule composition, task group composition and component composition. Two algorithms for performing composition are proposed. The first one is an extended Earliest Deadline First algorithm which can be used as a composability test for schedules. The second algorithm, the Harmonic Component Composition algorithm (HCC) provides an online admission test for components. HCC applies a rate monotonic classification of workloads and is a hard real-time solution because responsive supply of a shared resource is guaranteed for in-budget workloads. HCC is also efficient in terms of composability and requires low computation cost for both admission control and dispatch of resources.
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