Using design-level scan to improve FPGA design observability and controllability for functional verification

Abstract

This paper describes a structured technique for providing full observability and controllability for functionally debugging FPGA designs in hardware, capabilities which are currently not available otherwise. Similar in concept to flip-flop scan chains for VLSI, our design-level scan technique includes all FPGA flip-flops and RAMs in a serial scan chain using FPGA logic rather than transistor logic. This paper describes the general procedure for modifying designs with design-level scan chains and provides the results of adding scan to several designs, both large and small. We observed an average FPGA resource overhead of 84% for full scan and only 60% when we augmented existing FPGA capabilities with scan to provide complete observability and controllability in hardware.