Exploring FPGA Routing Architecture Stochastically

This paper proposes a systematic strategy to efficiently explore the design space of field-programmable gate array (FPGA) routing architectures. The key idea is to use stochastic methods to quickly locate near-optimal solutions in designing FPGA routing architectures without exhaustively enumerating all design points. The main objective of this paper is not as much about the specific numerical results obtained, as it is to show the applicability and effectiveness of the proposed optimization approach. To demonstrate the utility of the proposed stochastic approach, we developed the tool for optimizing routing architecture (TORCH) software based on the versatile place and route tool. Given FPGA architecture parameters and a set of benchmark designs, TORCH simultaneously optimizes the routing channel segmentation and switch box patterns using the performance metric of average interconnect power-delay product estimated from placed and routed benchmark designs. Special techniques - such as incremental routing, infrequent placement, multi-modal move selection, and parallelized metric evaluation - are developed to reduce the overall run time and improve the quality of results. Our experimental results have shown that the stochastic design strategy is quite effective in co-optimizing both routing channel segmentation and switch patterns. With the optimized routing architecture, relative to the performance of our chosen architecture baseline, TORCH can achieve average improvements of 24% and 15% in delay and power consumption for the 20 largest Microelectronics Center of North Carolina benchmark designs, and 27% and 21% for the eight benchmark designs synthesized with the Altera Quartus II University Interface Program tool. Additionally, we found that the average segment length in an FPGA routing channel should decrease with technology scaling. Finally, we demonstrate the versatility of TORCH by illustrating how TORCH can be used to optimize other aspects of the routing architecture in an FPGA.