Real-time synchronization between hard and soft tasks in RT-Linux

This paper presents the experience in adding a synchronization protocol to our architecture for flexible hard real-time systems. The architecture combines mandatory and optional components in a two-level tasking model. Mandatory and optional components share resources, and therefore synchronization is needed in order to maintain both the logical correctness of the resources and the timing correctness of the hard task set. Different approaches were analyzed and finally we implemented and evaluated both the Priority Ceiling Protocol (PCP) and the Ceiling Semaphore Protocol (CSP) within our run-time support system. Our results show that both methods can be made to work, but that the CSP method is generally more efficient and scales better