Application of Specific Delay Window Routing for Timing Optimization in FPGA Designs

Abstract

In addition to optimizing for timing performance and routability, commercial FPGA routing engines must also support various timing constraints enabling the designer to fine tune aspects of their design. The many intricacies of commercial FPGA architectures add difficulty to the problem of supporting such constraints. In this paper, we show how the method of specific delay window routing can be applied to optimize for these various timing constraints constituting both long- and short-path requirements. Additionally, we enhance existing methods of routing according to specified delay by using dual wave expansion instead of single wave expansion with target delay estimation in order to improve accuracy and support sparser, more varied interconnect structures. Our results show that specific delay window routing is well-suited for optimization targeting a variety of timing constraints, and that using dual wave expansion to eliminate the estimation part of the router's delay cost function enables the router to support tighter timing constraints. For a suite of designs with known hold timing violations, we found that the dual wave approach can correct all such violations, whereas the single wave approach failed to correct the hold timing violations for several designs. Furthermore, for a suite of designs with maximum skew constraints of 250 ps on certain nets and buses, the dual wave approach met the constraints for all designs, whereas the single wave approach failed to meet the constraints for a majority of the designs.