Analysis of operation of ring LFSR used for testing of unidirectional interleaved interconnections
Krzysztof Gucwa, Tomasz Garbolino, Andrzej Hławiczka · Elektronika : konstrukcje, technologie, zastosowania · 2011
The paper presents analysis of operation of a specific ring LFSR register that can be used to test a network of n interleaved interconnections between modules of digital circuits. This register is a distinctive option of the already known BIST structure referred to as CSTP. When the test is carried out for unidirectional interconnections, the CSTP becomes a linear register and the lines under test make up feedback lines of that register. Due to the fact that layout of these lines looks like the ‘X’ letter that register is referred to as the XR-LFSR. The fault-free XR-LFSR can be reflected by an automaton with the G 0 cyclic state diagram and each physical defect f transforms that G 0 state diagram into another state diagram G f ≠ G 0 . To verify its efficiency for detection of faults the method of state diagram identification was applied. The same authors in previous studies dedicated to bus-type connections observed that the sequence of m states of G 0 state diagram, where m > 2n and n > 16, is sufficient to detect a substantial number of static and delay faults for such buses. The present paper comprises the observation that any randomly selected state of the state diagram for the XR-LFSR belongs, with a pretty high level of probability, exceeding 70%, to the cycle with the maximum length c max . It was also spotted that for n>16 more than 98,4% of all structures lead to sufficiently long cycles c max > 1000. The both observations confirmed usefulness of XR-LFSRs for testing of unidirectional connections.