Improved trace buffer observation via selective data capture using 2-D compaction for post-silicon debug

This paper presents a novel technique for extending the capacity of trace buffers when capturing debug data during post-silicon debug. It exploits the fact that is it not necessary to capture error-free data in the trace buffer since that information can be obtained from simulation. A selective data capture method is proposed in this paper that only captures debug data during clock cycles in which errors are present. The proposed debug method requires only three debug sessions. The first session estimates a rough error rate, the second session identifies a set of suspect clock cycles where errors may be present, and the third session captures the suspect clock cycles in the trace buffer. The suspect clock cycles are determined through a 2-D compaction technique using multiple-input signature register signatures and cycling register signatures. Intersecting both signatures generates a small number of suspect clock cycles for which the trace buffer needs to capture. The effective observation window of the trace buffer can be expanded significantly, by up to orders of magnitude. Experimental results indicate very significant increases in the effective observation window for a trace buffer can be obtained.