Cluster Restoration-Based Trace Signal Selection for Post-Silicon Debug

Abstract

Trace signal selection is of great importance for post-silicon debug. Debuggers traditionally use state restoration to improve the observability of the trace data, and state restoration ratio (SRR) is computed after state restoration. In this paper, we exploit the combination of snapshot states and trace states to improve the observability. First, we propose a novel state restoration method, called cluster restoration. It uses both the snapshot states of flip-flop clusters at the beginning of tracing, and the tracing states of the clusters’ inputs during the tracing window to deterministically restore all states of these clusters during the tracing window. We also present a cluster restoration-based trace signal selection method to select clusters instead of trace signals directly, which includes two stages: 1) cluster generation and 2) cluster evaluation. For cluster generation, feedback loop-based cluster generation and backward tracing-based cluster generation techniques are proposed. For cluster evaluation, a new metric, called the global state restoration improvement is proposed to evaluate the candidate clusters. The experimental results show that in comparison to prior trace signal selection methods, our method can improve the SRR and reduce the runtime of trace signal selection as well.