Hierarchical multi-level fault simulation of large systems

This article discusses an approach for hierarchical multilevel fault simulation for large systems described at the transistor, gate, and higher levels. The approach reduces the memory requirement of the simulation drastically, thus allowing the simulation of circuits that are too large to simulate at one flat level on typical engineering workstations. This is achieved by exploiting the regularity and modularity found in a hierarchical circuit description that contains many repeated substructures. The hierarchical setup also allows flexible multilevel simulation: behavioral models can replace subcircuits at any level of the hierarchy for accelerated simulation. The simulation algorithms are at the switch level so that general MOS digital designs with bidirectional signal flow can be handled, and both stuck-at and transistor faults are treated accurately. The approach has been implemented in the hierarchical logic and fault simulation system, CHAMP, that runs under UNIX on SUN-3 and SUN-4 workstations. It has been used successfully for simulating and fault grading a large commercial microprocessor.