We consider a fully SAT-based method of unbounded symbolic model checking based on computing Craig interpolants. In benchmark studies using a set of large industrial circuit verification instances, this method is greatly more efficient than BDD-based symbolic model checking, and compares favorably to some recent SAT-based model checking methods on positive instances.

Interpolation and SAT-based model checking

Software-based self-test (SBST) techniques are used to test processors and processor cores against permanent faults introduced by the manufacturing process or to perform in-field test in safety-critical applications. However, the generation of an SBST program is usually associated with high costs as it requires significant manual effort of a skilled engineer with in-depth knowledge about the processor under test. In this paper, we propose an approach for the automatic generation of SBST programs. First, we detail an automatic test pattern generation (ATPG) framework for the generation of functional test sequences. Second, we describe the extension of this framework with the concept of a validity checker module (VCM), which allows the specification of constraints with regard to the generated sequences. Third, we use the VCM to express typical constraints that exist when SBST is adopted for in-field test. In our experimental results, we evaluate the proposed approach with a microprocessor without interlocked pipeline stages (MIPS)-like microprocessor. The results show that the proposed method is the first approach able to automatically generate SBST programs for both end-of-manufacturing and in-field test whose fault efficiency is superior to those produced by state-of-the-art manual approaches.

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A Flexible Framework for the Automatic Generation of SBST Programs

Vulnerabilities and design flaws in Network-on-Chip (NoC) routers can be exploited in order to spy, modify and constraint the sensitive communication inside the Multi-Processors Systems-on-Chip (MPSoCs). Although previous works address the NoC threat, finding secure and efficient solutions to verify the security is still a challenge. In this work, we propose for the first time a method to formally verify the correctness and the security properties of a NoC router in order to provide the proper communication functionality and to avoid NoC attacks. We present a generalized verification flow that proves a wide set of implementation-independent security-related properties to hold. We employ unbounded model checking techniques to account for the highly-sequential behaviour of the NoC systems. The evaluation results demonstrate the feasibility of our approach by presenting verification results of six different NoC routing architectures demonstrating the vulnerabilities of each design.

Towards the formal verification of security properties of a Network-on-Chip router

A variety of fault emulation systems have been created to study the effect of single-event effects (SEEs) in static random access memory (SRAM) based field-programmable gate arrays (FPGAs). These systems are useful for augmenting radiation-hardness assurance (RHA) methodologies for verifying the effectiveness for mitigation techniques; understanding error signatures and failure modes in FPGAs; and failure rate estimation. For radiation effects researchers, it is important that these systems properly emulate how SEEs manifest in FPGAs. If the fault emulation systems does not mimic the radiation environment, the system will generate erroneous data and incorrect predictions of behavior of the FPGA in a radiation environment. Validation determines whether the emulated faults are reasonable analogs to the radiation-induced faults. In this paper we present methods for validating fault emulation systems and provide several examples of validated FPGA fault emulation systems.

Validation Techniques for Fault Emulation of SRAM-based FPGAs

Software-based self-test (SBST) techniques are used to test processors against permanent faults introduced by the manufacturing process (often as a complementary approach with respect to DfT) or to perform in-field test in safety-critical applications. A major obstacle to their adoption is the high cost for developing effective test programs, since there is still a lack of suitable EDA algorithms and tools able to automatically generate SBST test programs. An efficient ATPG algorithm can serve as the foundation for the automatic generation of SBST test programs. In this work we first highlight the additional constraints characterizing SBST test programs wrt functional ones, with special emphasis on their usage for infield test; then, we describe an ATPG framework targeting stuck-at faults based on Bounded Model Checking. The framework allows the user to flexibly specify the requirements of SBST test programs in the considered scenario. Finally, we demonstrate how a set of properly chosen requirements can be used to generate test programs matching these constraints. In our experiments we evaluate the framework with the miniMIPS microprocessor. The results show that the proposed method is the first able to automatically generate SBST test programs whose fault efficiency is superior to those produced with state-of-the-art manual approaches.

On the automatic generation of SBST test programs for in-field test

Functional microprocessor test methods provide several advantages compared to DFT approaches, like reduced chip cost and at-speed execution. However, the automatic generation of functional test patterns is an open issue. In this work we present an approach for the automatic generation of functional microprocessor test sequences for small-delay faults based on Bounded Model Checking. We utilize an ATPG framework for small-delay faults in sequential, non-scan circuits and propose a method for constraining the input space for generating functional test sequences (i.e., test programs). We verify our approach by evaluating the miniMIPS microprocessor. In our experiments we were able to reach over 97 % fault efficiency. To the best of our knowledge, this is the first fully automated approach to functional microprocessor test for small-delay faults.

An effective approach to automatic functional processor test generation for small-delay faults

Functional test and software-based self-test (SBST) approaches for processors are becoming popular as they enable low-cost production tests and are often the only solution for in-field tests. With the increasing use of volume diagnosis, efficient and cost-effective diagnosis methods are required. A high quality functional or SBST test program can be used to perform logic fault diagnosis with low-cost test equipment and therefore significantly reduce the cost of diagnosis. We present a framework for the automatic generation of functional diagnostic sequences for stuck-at faults. The framework allows a user to specify constraints imposed by the employed test environment and generates diagnostic sequences satisfying these constraints. Furthermore, the framework is able to prove the equivalence of faults under the specified constraints. This enables to compute the best possible diagnostic quality that can be reached under the given environmental constraints. Also, it gives the necessary information for implementing selective DFT techniques in order to differentiate faults which cannot be distinguished otherwise. In our experiments we evaluated a MIPS-like processor. The results show that our approach can effectively distinguish fault pairs or prove their equivalence, under different environmental constraints. To the best, of our knowledge, this is the first approach which, enables the automatic generation of diagnostic SBST, programs and allows to eectively prove the equivalence of faults in functional and SBST test environments.

Effective generation and evaluation of diagnostic SBST programs

Manufactured VLSI circuits using a new technology typically suffer from systematic defects that are process-dependent and at sub-nanometer feature sizes such defects may be even design-dependent. The root causes for systematic defects must be determined to ramp up yields. Volume diagnosis is becoming popular to identify root causes for systematic defects. Volume diagnosis uses logic diagnosis based on failing circuit responses to production tests of a large number of failing devices, followed by statistical analysis methods to determine the root cause(s) for yield limiters. Typically production tests use fault detection tests and hence may have limited diagnosis resolution. To improve diagnosis resolution diagnostic ATPGs can be used to generate test sets to distinguish all pairs of distinguishable faults in one or more fault models. The sizes of such tests tend to be considerably higher than fault detection test sets used as production tests. For this reason, generation of test sets that detect faults and also possess a high diagnosis resolution is important. In this work we present a method to improve the diagnosis resolution of a compact fault detection test set without increasing pattern count or decreasing fault coverage. The basic idea of the approach is to generate a SAT formula which enforces diagnosis and is solved by a MAX-SAT solver which is a SAT-based maximization tool. We believe this is the first time a method to improve diagnosis resolution of a test set of given size has been reported. Experimental results on ISCAS 89 circuits demonstrate the effectiveness of the proposed method.

Andreas Riefert

Papers

A Flexible Framework for the Automatic Generation of SBST Programs

An effective approach to automatic functional processor test generation for small-delay faults

On the automatic generation of SBST test programs for in-field test

Effective generation and evaluation of diagnostic SBST programs

Improving diagnosis resolution of a fault detection test set