SlackProbe: A Low Overhead In Situ On-line Timing Slack Monitoring Methodology

In situ monitoring is an accurate way to monitor circuit delay or timing slack, but usually incurs significant overhead. We observe that most existing slack monitoring methods exclusively focus on monitoring path ending registers, which is not cost efficient from power and area perspectives. In this paper, we propose SlackProbe methodology, which inserts timing slack monitors like "probes" at a selected set of nets, including intermediate nets along critical paths. SlackProbe can significantly reduce the total number of monitors required at the cost of some additional delay margin. It can be used to detect impending delay failures due to various reasons (process variations, ambient fluctuations, circuit aging, etc.) and can be used with various preventive actions (e.g. voltage/frequency scaling, clock stretching/time borrowing, etc.). Though we focus on monitor selection in this work, we give an example of using SlackProbe with adaptive voltage scaling. Experimental results on commercial processors show that with 5% more timing margin, SlackProbe can reduce the number of monitors by 15-18X as compared to the number of monitors inserted at path ending pins.