Interstitial redundancy: an area efficient fault tolerance scheme for large area VLSI processor arrays

In the proposed scheme, spare PEs are located at interstitial sites within the array. Each spare can functionally replace any one of the neighboring primary PEs that are connected to it. Because spares are physically close to the PE that they replace, restructured interconnections are short, minimizing performance degradation. This structure can incorporate different levels of redundancy depending on how many of the interstitial sites are used to locate spares, and also how many spares are placed at each site. The author gives a polynomial time algorithm for assigning operational spares to failed primary PEs. He also gives area efficient layouts for such structures, and designs for implementing the switching network needed for reconfiguration. A procedure for deciding the optimum level of redundancy so as to maximize chip area utilization is also shown. The main attractive features of interstitial redundancy are short (fixed length) PE interconnections and high utilization of failure-free PEs. The analysis shows that for a wide range of array sizes and PE survival probabilities, 45-55 percent utilization of failure-free PEs on the chip can be achieved