We present an approach to bus access optimization and schedulability analysis for the synthesis of hard real-time distributed embedded systems. The  In this paper we concentrate on bus access optimization and schedulability analysis for the synthesis of embedded hard realtime systems which are implemented on distributed architectures consisting of multiple programmable processors and ASICs. Process scheduling is based on a static priority preemptive approach while the bus communication is statically scheduled. Process scheduling for performance estimation and synthesis of embedded systems has been intensively researched in the last years. Preemptive scheduling of independent processes with static priorities, running on single processor architectures has its roots in [8] . The approach has been later extended to accommodate more general computational models and has been also applied to distributed systems [17, 20] . Static non-preemptive scheduling of a set of processes on a multiprocessor architecture has been discussed in [4, 5] . Several approaches consider architectures consisting of a single programmable processor and an ASIC. Under such circumstances deriving a static schedule for the software component practically means the linearization of the dataflow graph [3] . Although different scheduling strategies have been adapted to accommodate distributed architectures, researchers have often ignored or very much simplified aspects concerning the communication infrastructure. One typical solution is to consider communication tasks as processes with a given execution time (depending on the amount of information transferred) and to schedule them as any other process [4, 20] , without considering issues like communication protocol, bus arbitration, packaging of messages, and clock synchronization. Previous works related to communication synthesis, like [1, 2, 6, 10, 11 ], are dealing with lower level aspects of hardwaresoftware communication and are not addressing problems specific to distributed real-time embedded systems, based on particular communication protocols. Currently, more and more real-time systems are used in physically distributed environments and have to be implemented on distributed architectures in order to meet reliability, functional, and performance constraints. Thus, in order to guarantee that real-time requirements are fulfilled, schedulability analysis has
REF proposes an approach for schedulability analysis of processes and message scheduling.
Bus access optimization for distributed embedded systems based on schedulability analysis