For multimedia applications, the System LSI design trend is to integrate an increasing number of applications running on a single chip. Traditional architectures have reached their limit in terms of performance. New architectures must be explored to fulfill the system application needs. Complex bus structures have been introduced. These bus architectures open a much larger exploration space than traditional hardware-software partitioning trade-offs. We have been researching methods to leverage these new architectural elements. We also introduce a design environment to apply practical and efficient methods in today's design flow. Two key technologies are supporting our method and environment: Automatic bus architecture synthesis for easy configuration of bus architecture and transaction level of abstraction for communication for improvement of simulation performance. In this paper, we show the design method, an overview of the design environment and its usefulness through experimental results.