LFSR generation for high test coverage and low hardware overhead

Abstract

Safety-critical technology rests on optimised and effective testing techniques for every embedded system involved in the equipment. Pattern generator (PG) such as linear feedback shift register (LFSR) is used for fault detection and useful for reliability and online test. This study presents an analysis of the LFSR, using a known automatic test PG (ATPG) test set. Two techniques are undertaken to target difficult-to-detect faults with their respective trade-off analysis. This is achieved using Berlekamp-Massey (BM) algorithm with optimisations to reduce area overhead. The first technique (concatenated) combines all test sets generating a single polynomial that covers complete ATPG set (baseline-C). Improvements are found in Algorithm 1 reducing polynomial size through Xs assignment. The second technique uses non-concatenated test sets and provides a group of LFSRs using BM without including any optimisation (baseline-N). This algorithm is further optimised by selecting full mapping and independent polynomial expressions. Results are generated using 32 benchmarks and 65 nm technology. The concatenated technique provides reductions on area overhead for 90.6% cases with a best case of 57 and 39% means. The remaining 9.4% of cases, non-concatenated technique provides the best reduction of 37 with 1.4% means, whilst achieving 100% test mapping in both cases.