Trace-Based Post-Silicon Validation for VLSI Circuits

Abstract

The ever-increasing design complexity of modern circuits challenges our ability to verify their correctness. Therefore, various errors are more likely to escape the pre-silicon verification process and to manifest themselves after design tape-out. To address this problem, effective post-silicon validation is essential for eliminating design bugs before integrated circuit (IC) products shipped to customers. In the debug process, it becomes increasingly popular to insert design-for-debug (DfD) structures into the original design to facilitate real-time debug without intervening the circuits’ normal operation. For this so-called trace-based post-silicon validation technique, the key question is how to design such DfD circuits to achieve sufficient observability and controllability during the debug process with limited hardware overhead. However, in today’s VLSI design flow, this is unfortunately conducted in a manual fashion based on designers’ own experience, which cannot guarantee debug quality. To tackle this problem, we propose a set of automatic tracing solutions as well as innovative DfD designs in this thesis. First, we develop a novel trace signal selection technique to maximize the visibility on debugging functional design errors. To strengthen the capability for tackling these errors, we sequentially introduce a multiplexed signal tracing strategy with a trace signal grouping algorithm for maximizing the probability of catching the propagated evidences from functional design errors. Then, to effectively localize speedpath-related electrical errors, we propose an innovative trace signal selection solution as well as a trace qualification technique. On the other hand, we introduce several low-cost interconnection fabrics to effectively transfer trace data in post-silicon validation. We first propose to reuse the existing test channel for real-time trace data transfer, so that the routing cost of debug hardware is dramatically reduced. The method is further improved to avoid data corruption in multi-core debug. We then develop a novel interconnection fabric design and optimization technique, by combining multiplexor network and non-blocking network, to achieve high debug flexibility with minimized hardware cost. Moreover, we introduce a hybrid trace interconnection fabric that is able to tolerate unknown values in “golden vectors”, at the cost of little extra DfD overhead. With the fabric, we develop a systematic signal tracing procedure to automatically localize erroneous signals with just a few debug runs. Our empirical evaluation shows that the solutions presented in this thesis can greatly improve the validation quality of VLSI circuits, and ultimately enable the design and fabrication of reliable electronic devices.