Post-Silicon Gate-Level Error Localization with Effective & Combined Trace Signal Selection

Incorporating on-chip trace buffers helps to overcome the limited observability by tracing selected signals during post-silicon validation. The effectiveness of trace buffer-based techniques largely relies on selection of appropriate trace signals. For processor-based systems, the selection becomes relatively easier because important signals can be identified. However, for a general digital block in a complex SoC, recognizing necessary trace signals becomes extremely challenging and requires a systematic approach. Previous research on trace signal selection has mainly focused on improving reconstruction of unknown signal values with the help of traced signals. Even though it serves as a good selection principle, an effective signal selection must consider other important factors such as error detection with the traced signals, which in turn assist in localization and root-cause discovery. Additionally, from practical point of view, the signal selection algorithm needs to cater to factors like routing congestion and minimizing routing wire length. The proposed methodology of signal selection attempts to combine these three crucial factors of signal selection: restoration of untraced signal states, error detection with traced signals and routing considerations. The concurrent maximization of all these three parameters is difficult as they have conflicting preference of the candidate trace signals. Hence, the proposed signal selection approach presents a methodology of judiciously mixing the choices of these three objectives. Furthermore, the restored and traced signal states are analyzed for the purpose of error localization at the gate level for several design error models.