Efficient sequential ATPG for functional RTL circuits

We present an efficient register-transfer level automatic test pattern generation (ATPG) algorithm. First, our ATPG generates a series of sequential justification and propagation paths for each RTL primitive via a deterministic branch-and-bound search process, called a test environment. Then the pre-computed test vectors for the RTL primitives are plugged into the generated test environments to form gate-level test vectors. We augment a 9-valued algebra to efficiently represent the justification and propagation objectives at the RT Level. Our ATPG automatically extracts any finite state machine (FSM)from the circuit, constructs the state transition graph (STG), and uses high-level information to guide the search process. We propose new static methods to identify embedded counter structures, and we use implication-based techniques and static learning to find the FSM traversal sequences sufficient to control the counters. Finally, a simulation-based RTL extension is added to augment the deterministic test set in a few cases when there is additional room for the improvement in fault coverage. Experimental results show that our new deterministic RTL techniques achieve several orders of magnitude reduction of test generation time without compromising fault coverage when compared to gate-level ATPG tools. Our ATPG also outperforms a recently reported simulation-based high-level ATPG tool in terms of both fault coverage and CPU time.