Growing design complexity has made functional debugging of application-specific integrated circuits crucial to their development. Two widely used debugging techniques are simulation and emulation. Design simulation provides good controllability and observability of the variables in a design, but is two to ten orders of magnitude slower than the fabricated design. Design emulation and fabrication provide high execution speed, but significantly restrict design observability and controllability. To facilitate debugging, and in particular error diagnosis, we introduce a novel cut-based functional debugging paradigm that leverages the advantages of both emulation and simulation. The approach enables the user to run long test sequences in emulation, and upon error detection, roll-back to an arbitrary instance in execution time, and transparently switch over to simulation-based debugging for full design visibility and controllability. The new debugging approach introduces several optimization problems. We formulate the optimization tasks, establish their complexity, and develop most-constrained least-constraining heuristics to solve them. The effectiveness of the new approach and accompanying algorithms is demonstrated on a set of benchmark designs where combined emulation and simulation is enabled with low hardware overhead.
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