It is essential to cut down the fabrication cost especially in mass production. This paper presents a design methodology in which we reduce the operating frequency of a communication bus under hard real-time constraints so that we can cut down the cost of a communication mechanism of an in-vehicular embedded system. The reduction of the operating frequency contributes to choosing a slower and cheaper wire harness that constitutes an in-vehicular network system. We formalize a bus bandwidth minimization problem to optimize a payload size of a frame under hard real-time constraints on the assumption that each and every signal is uniquely mapped to its own time slot of the time division multiple access (TDMA) scheme. Our experimental results show that our methodology obtained an optimal payload size of a frame and an optimal operating frequency of a bus for several hypothetical automotive benchmarks. Our method achieved one-fifth of the typical bandwidth of a FlexRay bus, that is 10 Mbps, for the SAE benchmark signal set.

Industrial applications such as automotive ones require a cheap communication mechanism to send out communication messages from node to node by their deadline time. This paper presents a design paradigm in which we optimize slot multiplexing of a FlexRay bus under hard real-time constraints so that we can minimize the operating frequency of the FlexRay bus. The reduction of the operating frequency of a FlexRay bus helps one to choose a slower and cheaper wire harness for building a distributed system. We formulate a slot multiplexing optimization problem under hard real-time constraints. We build an integer linear programming (ILP) model as a means for solving the slot multiplexing optimization problem. Our experimental results show that our design paradigm achieved a 72.7% smaller operating frequency at its best than the naive one.

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