Evaluating fault-tolerance of redundant FPGA structures using Boolean difference calculus

The reliability of FPGA based hardware designs has become an important field of research particularly for space computing. Traditionally, redundancy is utilized in FPGA based designs to achieve reliable or error-tolerant computing. However, the redundant designs vary according to the granularity level and the voter placement algorithms used for the hardware design. The resulting circuit configurations vary in area, latency and power as well as in the achieved reliability. While the evaluation of area, latency and power is done by the FPGA design tools, quantitative data for reliability are usually not derived. Consequently, there is a need for an automated reliability evaluation tool especially considering the huge design space of redundant circuit structures. In this paper, we combine the Boolean difference error calculator (BDEC), a probabilistic reliability model for hardware designs, with a reliability model for fault-tolerant circuit structures. As a result, we are able to study the reliability of fault-tolerant circuit structures at the logic layer. We focus on fault-tolerant circuits to be implemented in FPGAs and show how to extend our combined model from combinational to sequential circuits. For an automated analysis, we develop a MATLAB-based tool utilizing our extended BDEC model. With this tool, we conduct a case study on dynamic reliability management and show how quantitative reliability data obtained from this tool improves the four-dimensional Pareto optimization for area, latency, power and reliability.