A fault list analysis methodology is proposed to determine how many Cell-Aware Test (CAT) defects can be detected by test patterns generated targeting the other fault models, including stuck-at faults (SAFs), transition-delay faults (TDFs), and small-delay defects (SDDs). Our analysis reveals that a proper ordering in fault simulation can accelerate the CAT fault simulation process. We evaluated our approach on a RISC-V core, synthesized using an industrial technology library. We demonstrated an innovative method to optimize CAT fault simulation by means of preliminary static fault list analysis, resulting in fault simulation runtime reduction of up to 80% for static and 35% for dynamic CAT faults.

Software-Based Self-Test (SBST) is vastly adopted as a hardware safety mechanism for the in-field test of safety-critical systems in the form of Software Test Libraries (STLs). Typically, an STL’s diagnostic coverage is evaluated on the stuck-at fault model. As various defect-oriented fault models exist and are used for manufacturing testing, such as the popular cell-aware test (CAT), there is a need to evaluate the effectiveness of SBST when such models are targeted. This work targets static CAT faults. We evaluated the fault coverage of open-available STLs for a RISC-V SoC. We used results stemming from stuck-at fault simulation and gate-exhaustive simulation to elaborate on the obtained results.

In-field test of microprocessors is a major topic for the industry, especially in the safety-critical domain, where the respective standards mandate high test coverage thresholds. The dominant fault models used are the transition delay and the stuck-at fault model. However, the adoption of very advanced semiconductor technologies to manufacture devices used in safety-critical applications pushes toward considering new fault models that are better suited to catch subtle and age-related defects. Among the other phenomena, latent cell-internal defects emerged as relevant causes for several failures. Hence, the necessity for the Cell-Aware Test (CAT) was born, and the inclusion of the CAT fault model in the latest safety standards. Although CAT amends the issue of the numerous test escapes, it may suffer as well from the presence of functionally untestable faults that may pollute the overall test efficiency with their presence. In this paper, we propose a solution, based on formal methods, for the automatic identification of functionally untestable faults under the Cell-Aware fault model for the case where the DUT is a fully pipelined processor. As a case study, we used the RISC-V processor RI5CY for which we applied the minimum constraints required to ensure a functional behavior to demonstrate the effectiveness and impact of the approach. With the considered constraints, a significant percentage of functionally untestable faults was located in the several modules within the processor. Furthermore, the method allows to flexibly take into account any constraint stemming from the system configuration and the application. The obtained results have been validated by resorting to commercial EDA tools.

Electronics employed in modern safety-critical systems require severe qualification during the manufacturing process and in the field, to prevent fault effects from manifesting themselves as critical failures during mission operations. Traditional fault models are not sufficient anymore to guarantee the required quality levels for chips utilized in mission-critical applications. The research community and industry have been investigating new test approaches such as device-aware test, cell-aware test, path-delay test, and even test methodologies based on the analysis of manufacturing data to move the scope from OPPM to OPPB. This special session presents four contributions, from academic researchers and industry professionals, to enable better chip quality. We present results on various activities towards this objective, including device-aware test, software-based self-test, and memory test.