Determining Bus Arbitration Policies and Data Transfer Techniques for Multiprocessor Systems

Abstract

A Wtional approach to the minimization of communication latency in areal-time multiprocessor system is to reduce the interprocessor communication software overhead and to use a high bandwidth communication link. Of equal importance, but often overlooked, is the reduction of the link waiting time during interprocessor arbitration by the proper selection of the arbitration policies and data transfer techniques to use along the link. This paper discusses these two fundamental topics and identifies the on-link and off-link times of the data transfers to be key system parameters that can be used to control and reduce this portion of the communication latency. A methodology is described for determining these times, the latency expected for the application, and the number of processors that can be supported for each arbitration policy and data transfer technique of interest, System parameters, taken from our lab VMEbus system, are used to demonstrate the methodology. Results were verified by actual performance of skeletonized test applications built along the guidelines of the NASREM robot control architecture. With a firm understanding of the system parameters contributing to this portion of the latency, the system designer can then examine the tradeoffs between adding communication pathways or changing transfer techniques and arbitration policies in new systems, or discover and correct potential problems in existing ones.