An industrial case study for X-canceling MISR

An X-tolerant multiple-input signature register (MISR) compaction methodology that compacts output streams containing unknown (X) values was described in [Touba 07]. Unlike conventional approaches, it does not use X-masking logic at the input of the MISR. Instead it uses symbolic simulation to express each bit of the MISR signature as a linear equation in terms of the X's. Linearly dependent combinations of the signature bits are identified with Gaussian elimination and XORed together to cancel out all X values and yield deterministic values. This new X-canceling approach was applied to some industrial designs under the constraints imposed by an industrial test environment. Practical issues for implementing X-canceling are discussed, and a new architecture for implementing X-canceling based on using a shadow register with multiple selective XORs is presented. Experimental results are shown for industrial designs comparing the performance of X-canceling with X-compact.