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UBC Theses and Dissertations

BackSpace : formal analysis for post-silicon debug De Paula, Flavio Miana


IC technology continues to closely follow Moore's Law, while the ability to verify designs lags behind. The International Technology Roadmap for Semiconductors (ITRS) predicts production of chips using 16nm technology already by 2015, but the verification gap, i.e., advancements in verification technology not keeping up with advancements in design technology, seems to be also increasing at a fast pace. A recent study shows a drop of more than 10 percentage points in the number of 1st-silicon success from 2002 through 2009. By 2007, more than 2/3 of chips had to be respun due to bugs. The increasing verification gap is to blame. Unfortunately, because more bugs are slipping into the fabricated chip, post-silicon debug is the only way to catch them. Post-silicon debug is the problem of determining what's wrong when the fabricated chip of a new design behaves incorrectly. The focus of post-silicon debug is design errors, whereas traditional VLSI test focuses on random manufacturing defects on each fabricated chip. Post-silicon debug currently consumes more than half of the total verification schedule on typical large designs, and the problem is growing worse. The general problem of post-silicon debug is broad and multi-faceted, spurring a diverse variety of research. In this thesis, I focus on one of the most fundamental tasks: getting an execution trace of on-chip signals for many cycles leading up to an observed bug or crash. Until such a trace is obtained, further debugging is essentially impossible, as there is no way to know what happened on the chip. However, the ever-increasing chip complexity compounded with new features that add non-determinism makes computing accurate traces extremely difficult. Thus, to address this issue, I present a novel post-silicon debug framework, which I call BackSpace. From theory to practice, I have methodically developed this framework showing that BackSpace effectively computes accurate traces leading up to a crash state, has low cost (zero-additional hardware overhead), and handles non-determinism. To support my claims, I demonstrated BackSpace with several industrial designs using simulation models, hardware prototypes, and on actual silicon.

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