Efficient Selection of Trace and Scan Signals for Post-Silicon Debug

Post-silicon validation is a critical part of integrated circuit design methodology. The primary objective is to detect and eliminate the bugs that have escaped pre-silicon validation phase. One of the key challenges in post-silicon validation is the limited observability of internal signals in manufactured chips. A promising direction to improve observability is to combine trace and scan signals-a small set of trace signals are stored in every cycle, whereas a large set of scan signals are dumped across multiple cycles. Existing techniques are not very effective, since they explore a coarse-grained combination of trace and scan signals. In this paper, we propose a fine-grained architecture that addresses this issue using various scan chains with different dumping periods. We also propose efficient algorithms to select beneficial signals based on this architecture. Our experimental results demonstrate that our approach can improve restoration ratio up to 127% (36% on average) compared with existing trace-only techniques. Our approach also shows up to 125% improvement (61.7% on average) compared with techniques that allow a combination of trace and scan signals with minor (<;1%) area and power overhead.

I. Introduction

The goal of post-silicon validation of an integrated circuit is to ensure that the fabricated, preproduction silicon operates correctly under actual operating conditions with real application. It is a complex activity performed under aggressive schedules, representing >50% of the overall validation cost [1]. A fundamental challenge in post-silicon validation is limited observability and controllability. Due to the limitations in the number of output pins and area and power overheads of internal trace buffer, only a small percentage of internal signals in the design can be observed during silicon execution. Furthermore, in order for a signal to be observed, the design must be instrumented a priori with appropriate control hardware that routes a signal to an observation point. It is, therefore, crucial to identify trace signals that maximize design visibility and debug information under the observability constraints.