Two-stage physical synthesis for FPGAs

This paper presents an overview of an industrial physical synthesis CAD flow for FPGAs. The flow provides a performance speedup of 10%-15% for most circuits, and a significant number of circuits show a speedup of 20%-180%. We describe the algorithms used to achieve this result including: incremental retiming, BDD-based resynthesis, local rewiring, and logic replication. The effectiveness of these operations depends on the ability to accurately determine which portions of logic are timing critical at a stage of the CAD flow where there is still freedom to perform logic restructuring. We show how this problem can be effectively solved by inserting prediction and restructuring operations at multiple points of the FPGA CAD flow.