Implementation of overrun and skipping in VxWorks

In this paper we present our work towards allowing for dependence among partitions in the context of hierarchical scheduling of software systems with real-time requirements, and we present two techniques for cross-partition synchronization. We have earlier developed a Hierarchical Scheduling Framework (HSF) in VxWorks for independent real-time tasks, and in this paper we extend the HSF implementation with capabilities of synchronization between tasks resident in two different partitions. In particular, we have implemented the overrun and skipping mechanisms in our modular scheduling framework. Our framework has a key characteristic of being implemented on top of the operating system, i.e., no modifications are made to the kernel. Such a requirement enforce some restrictions on what can be made with respect to the implementation. The evaluation performed indicates that, under the restrictions of not modifying the kernel, the skipping mechanism has a much lower implementation overhead compared to the overrun mechanism