First silicon, the initial prototype of a new chip design, often involves days of tedious, labor-intensive debugging and mask repairs before production-ready chips can be produced. Most problems with initial prototypes can be diagnosed, but repairing problems deep inside a chip becomes increasingly difficult as design rules shrink and mask levels are added. Some have proposed adding extra tunable structures to affect repairs post-silicon. FogClear, a software-only approach to post-silicon debugging, was unveiled this week by University of Michigan researchers at the International Conference on Computer-Aided Design. FogClear aims to make obsolete the "first silicon" moniker by repairing errors in prototypes in hours rather than days. Proponents said this can be accomplished by merely changing one of the top interconnection layers.