Improving testability and soft-error resilience through retiming

Abstract

State elements are increasingly vulnerable to soft errors due to their decreasing size, and the fact that latched errors cannot be completely eliminated by electrical or timing masking. Most prior methods of reducing the soft-error rate (SER) involve combinational redesign, which tends to add area and decrease testability, the latter a concern due to the prevalence of manufacturing defects. Our work explores the fundamental relations between the SER of sequential circuits and their testability in scan mode, and appears to be the first to improve both through retiming. Our retiming methodology relocates registers so that 1) registers become less observable with respect to primary outputs, thereby decreasing overall SER, and 2) combinational nodes become more observable with respect to registers (but not with respect to primary outputs), thereby increasing scantestability. We present experimental results which show an average decrease of 42% in the SER of latches, and an average improvement of 31% random-pattern testability. Copyright 2009 ACM.