Defect recovery in nanodevice-based programmable interconnects (abstract only).

This work focuses on defect tolerance for nanodevice-based programmable interconnects of FPGAs. A single nanodevice can function as a routing switch in place of a pass transistor and its six-transistor SRAM cell in conventional FPGAs. Defects of nanodevices in programmable interconnects are manifested as losses of configurability and can be categorized into stuck- open defect and stuck- closed defect. First, we show that the stuck-closed defects of nanodevices have a much higher impact than the stuck-open defects. Instead of simply avoiding the stuck-closed defects, we recover them by treating them as shorting constraints in the routing. We develop a scalable algorithm to perform timing-driven routing under these extra constraints. We extend the idea of the resource negotiation to balance the goals of timing and routability under shorting constraints. We also develop several techniques to guide the router to map the shorting clusters to those nets with more shared paths for better utilization of routing resources while automatically balancing it with circuit performance. We also enhance the placement algorithm to recover logic blocks which become virtually unusable due to shorted pins. Simulation results show that at the up-to-date level of nanodevice defects (108-1011x higher than CMOS), compared to the simple avoidance method, our approach reduces the degradation of resource usage by 87%, improves the routability by 37%, and reduce the degradation of circuit performance by 36%, at a negligible overhead of tool runtime.