New semiconductor technologies for advanced applications are more prone to defects and imperfections related, among several different causes, to the manufacturing process, aging, and cross-talks. These phenomena negatively affect the circuit’s timing and can be effectively modeled by means of the path delay fault (PDF) model. While path delay testing is currently supported by commercial automatic test pattern generation tools for scan designs, functional testing covering PDFs is not widely adopted, mainly because of the high cost for test generation. On the other side, functional test is already widely adopted for in-field test of stuck-at faults (SAFs), which is often performed resorting to the execution of suitable test programs (Self Test Libraries, or STLs). This approach is attractive, since it can be performed at-speed with limited time constraints and high flexibility, making it a suitable in-field test solutions. Previous work assessed the feasibility and validity of functional approaches based on test programs targeting PDFs. In this work, we present the first systematic method for the development of very high fault coverage test programs for PDFs, which largely outperform test programs written for other fault models. Moreover, the proposed method allows the identification of functionally untestable faults. The effectiveness of the proposed approach was proven on an open-source RISC-V processor core, where 100% coverage of the functionally testable longest paths was achieved, compared with an initial coverage of 0.52% achieved with test programs targeting SAFs. Results demonstrate that shorter paths are also effectively covered.

In-field test of integrated circuits using Self-Test Libraries (STLs) is a widely used technique specifically suited to guarantee the processor’s correct behavior during the operative lifetime, as mandated by functional safety standards such as ISO26262. Developing STLs for stuck-at faults requires significant manual efforts from test engineers, and targeting delay faults is even more challenging. In order to support this process, in this paper we propose a method to automate the creation of STLs targeting delay faults starting from existing STLs targeting stuck-at faults. The method is based first on identifying excited but not-observed transition delay faults and then adding suitable instructions able to detect them. Experimental results on a RISC-V processor show that the method can systematically detect a significant percentage of the target faults with reasonable computational effort and test code size increase.

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.

Functional test using a Software Test Library (STL) is becoming a standard solution for the in-field test of safety-critical systems, in compliance with functional safety standards, such as the ISO26262 for the automotive domain. However, developing high-quality test programs is considerably more challenging than generating scan test patterns through commercial tools, mainly due to the lack of mature EDA tools. As a result, in many cases, the effort needed to reach the target fault coverage is not affordable. In this paper, we propose a methodology to improve the fault coverage of an STL using already available hardware resources. The proposed approach identifies the set of sequential cells that capture fault effects before being masked during their propagation towards observable points. Using a heuristic set covering approach, we select the subset of flip-flops needed to reach the target fault coverage, and exploit post-silicon debug hardware to make fault effects observable. Experimental results gathered on an open-source RISC-V core show significant improvements in the stuck-at and delay fault coverage values.

Testing digital integrated circuits is generally done using Design-for-Testability (DfT) solutions. Such solutions, however, introduce non-negligible area and timing overheads that can be overcome by adopting functional solutions. In particular, functional test of integrated circuits plays a key role when guaranteeing the device's safety is required during the operative lifetime (in-field test), as required by standards like ISO26262. This can be achieved via the execution of a Self-Test Library (STL) by the device under test (DUT). Nevertheless, developing such test programs requires a significant manual effort, and can be non-trivial when dealing with complex modules. This paper moves the first step in defining a generic and systematic methodology to improve transition delay faults' observability of existing STLs. To do so, we analyze previously devised STLs in order to highlight specific points within test programs to be improved, leading to an increase in the final fault coverage.

The development of Integrated Circuits for the Automotive sector imposes on major challenges. ISO26262 compliance, as part of this process, entails complex analysis for the evaluation of potential random hardware faults. This paper proposes a systematic approach to identify faults that do not disrupt safety-critical functionalities and consequently can be considered Safe. By deploying code coverage and Formal verification techniques, our methodology enables the classification of faults that are unclassified by other technologies, improving ISO26262 compliance. Our results, in combination with Fault Simulation, achieved a Diagnostic Coverage of 93% in a CAN Controller. These figures allow an initial assessment for an ASIL B configuration of the IP.

Path Delay fault test currently exploits DfT-based techniques, mainly relying on scan chains, widely supported by commercial tools. However, functional testing may be a desirable choice in this context because it allows to catch faults at-speed with no hardware overhead and it can be used both for end-of-manufacturing tests and for in-field test. The purpose of this article is to compare the results that can be achieved with both approaches. This work is based on an open-source RISC-V-based processor core as benchmark device. Gathered results show that there is no correlation between stuck-at and path delay fault coverage, and provide guidelines for developing more effective functional test.

The Controller Area Network (CAN) bus is a serial bus protocol widely used in the automotive domain to allow communication between different Electronic Control Units in the car. Being often part of safety-critical systems, the hardware implementing the CAN network must be constantly tested along the system lifetime, even during the operational phase. CAN controllers are relatively complex modules in charge of managing the sending and the receiving of packages through the CAN bus and defects affecting them can easily compromise the whole CAN network. In this work, the CAN controller is tested by test programs to be executed by the CPU connected to the device under test and by another unit connected to the same CAN bus. A fault grading with respect to structural permanent faults of a functional test based on the execution of a software test library for the CAN bus is presented for the first time. Results show how the approach can cover more than 90% of stuck-at faults on an open-source implementation of the standard, which is significantly more than what a usual functional test based on some sample application can achieve.