Abstract. This paper presents a modification of GLADE -the current GNAT implementation of the Ada 95 Distributed Systems Annex (DSA)-to support the development of distributed applications with hard real-time requirements. This modified implementation, that we call RT-GLADE (Real-Time GLADE), is specially suitable for embedded applications composed of a small number of heterogeneous processors and communication networks, because it ensures predictable timing behaviour. A real-time model of the implementation allows the application developer to determine and optimize the overall timing behaviour by applying the corresponding schedulability analysis and priority assignment techniques. This realtime version of GLADE continues to conform to the DSA, so the entire real-time application can be built within the Ada 95 context. To implement RT-GLADE, we provide a priority-based communication network over standard Ethernet that is used to ensure predictable transmission times.

Abstract. When a middleware layer is designed for providing semi-transparent distribution facilities to real-time applications, a trade-off must be made between the expressiveness and control capabilities of the real-time parameters used, and the simplicity of usage. Middleware specifications such as RT-CORBA or Ada's Distributed Systems Annex (DSA) rely on the use of priorities to map the timing requirements of the application, thus restricting the possible scheduling policies. This paper presents a generic technique to express complex scheduling and timing parameters of distributed transactions, allowing real-time middleware implementations to change their scheduling policies for both the processing nodes and the networks. The technique has been tested in an implementation of Ada's DSA, providing two interchangeable policies: a fixed-priority scheduler, and a complex contract-based flexible scheduler.