FCRoute: A Fast FPGA Connection Router Using Soft Routing-Space Pruning Algorithm

Abstract

Routing is one of the most time-consuming stages in the field-programmable gate array (FPGA) design flow. Even if various attempts have been made to reduce route time, the existing work rarely focuses on improving the underlying A*-based FPGA connection router. In this article, we present a fast FPGA connection router called FCRoute based on a novel soft routing-space pruning algorithm. Within FCRoute, a routing resource priority mechanism is applied to classify the routing resource nodes into high-priority nodes and low-priority ones. On the whole, FCRoute is composed of fast maze search and backtracking process. During the fast maze search, we explore only the high-priority nodes in the routing space. In this way, a great deal of unnecessary work can be avoided. When the fast maze search fails to find the target sink, it allows the backtracking process to explore the low-priority nodes promising to be on the best path, after which a new fast maze search is called. By avoiding the exploration of the majority of low-priority nodes, FCRoute maintains runtime efficiency while ensuring global search ability. In addition, we further accelerate FCRoute with an engineering enhancement which simplifies the cost computations of nodes. Runtime and quality of results are compared with the state-of-the-art connection router in VPR 8. Experimental results show that on average FCRoute explores less than half the number of routing resource nodes, and therefore reduces runtime by 38% while enabling the quality of results. When combined with the enhancement, FCRoute achieves an average 45% reduction on runtime without sacrificing the quality of results.