A Boolean satisfiability-based incremental rerouting approach with application to FPGAs

Incremental redesign is an increasingly essential step in any complex design. Late changes or corrections in functional specifications (so-called "engineering change orders" or ECOs) force us to search for a minimal perturbation that achieves the desired repair. In reconfigurable design scenarios, these incremental repairs may be in response to physical faults: the goal is to "design around" the fault. For FPGAs, incremental rerouting is an essential component of this repair problem. We have developed a new incremental rerouting algorithm for FPGAs using techniques from Boolean Satisfiability (SAT). In this application, these techniques have the twin virtues that they (1) represent all possible routing (and rerouting) constraints simultaneously and exactly, and (2) search for rerouting solutions by perturbing all nets concurrently. Preliminary results are promising. For several FPGA benchmarks, we were able to reroute fault reconfigurations that perturb up to 5.74% of all nets for a small number of fault sets (one to four faults) with only 1.55 track overhead per channel on average, with CPU time 0.76 to 4.91 seconds/fault.