Maurizio Damiani

Estimate of signal probability in combinational logic networks

Two methods for the calculation of node signal probabilities in combinational networks are presented. These techniques provide a better accuracy than existing algorithms and a deeper insight in the effects of first-order correlations due to multiple fan-out reconvergences. The proposed algorithms are shown to compare favorably with existing procedures in the analysis of significant benchmarks, both in accuracy and in computational efficiency.<<ETX>>

The disjunctive decomposition of logic functions

We present an algorithm for extracting a disjunctive decomposition from the BDD representation of a logic function F. The output of the algorithm is a multiple-level netlist exposing the hierarchical decomposition structure of the function. The algorithm has theoretical quadratic complexity in the size of the input BDD. Experimentally, we were able to decompose most synthesis benchmarks in less than one second of CPU time, and to report on the decomposability of several complex ISCAS combinational benchmarks. We found the final netlist to be often close to the output of more complex dedicated optimization tools.

Aliasing in signature analysis testing with multiple input shift registers

An investigation of the properties of multiple input shift registers for signature analysis is presented. The assumption of independent errors at the register inputs has been used to model the register behavior as a Markov process whose equations have been solved to obtain the exact dependence of aliasing probabilities as a function of test length, input error probabilities, and feedback structure. Some unique featured of maximum-length registers are proven. Accurate simplified expressions of aliasing probability are derived for use as tools in the evaluation of the coverage. >

Novel design for testability schemes for CMOS ICs

The authors present ideas for addressing the problem of detecting non-stuck-at faults in CMOS circuits that cannot be revealed by means of conventional methods (i.e., as logical errors in the steady-state response). Two techniques are proposed for detecting analog faults, particularly those resulting in intermediate voltages along circuit branches due to faulty conductive paths between the power supply and ground. Involving the conversion of analog faults into stuck-ats and the use of distributed testing logic, these techniques are shown to avoid the drawbacks of previous solutions. A method is proposed for online detection of delay faults, so far not yet considered in the context of design-for-testability. All the proposed techniques require little extra hardware and lead to minimal performance degradations. >

An analytical model for the aliasing probability in signature analysis testing

The Markov chain model of linear feedback shift-registers (LFSRs) for signature analysis testing is analytically solved to obtain the exact expression of the aliasing error probability as a function of test length, error probability, and the structure of the feedback network. The dependence on feedback configuration is explored in depth, and it is proven that maximum-length LFSRs have the best performances with respect to aliasing, regardless of the particular structure of their feedback network. Simplified expressions of aliasing probability are also derived for use as practical tools to design LFSRs for IC signature analysis testing, and a heuristic criterion is given for the identification of peaks in aliasing probability. >

Analysis and design of linear finite state machines for signature analysis testing

The authors present a theoretical investigation of the aliasing error probability (AEP) in signature analysis testing by means of linear finite state machines (LFSMs). The equations of the resulting Markov chain model of the LFSM are solved to determine an exact expression of the AEP as a function of the main LFSM features and of the relevant parameters of the testing environment. This expression is used to prove criteria for the synthesis of LFSMs with minimum asymptotic and transient AEP. A fundamental lower bound on the AEP is presented, which represents the performance limit of any LFSM with respect to aliasing minimization. It is shown that the AEP in machines realizing counters mod 2/sup k/-1 is the closest to such a bound, in particular periodically reaching it. >

Testability measures in pseudorandom testing

The authors present two methods for computing the fault detection probabilities in combinational networks. The methods provide a deeper insight into the effects of signal correlations caused by multiple fan-out reconvergencies and can be used in testability analysis to predict the fault coverage of pseudorandom patterns. The performances of these algorithms have been tested on significant benchmarks and compare favorably with those of previous procedures. >

Fault simulation of unconventional faults in CMOS circuits

The authors present a novel technique to study the detection of non-stuck-at faults in CMOS circuits. Gate-level models of CMOS faults not yet adequately covered in the literature are developed. Suitable models for transistor stuck-open and stuck-on, gate-drain shorts, and bridgings are implemented in a fault simulator. Results obtained with typical circuits are presented and discussed to analyze the influence of circuit architecture and type of test vector (deterministic or pseudorandom) on the coverage of non-stuck-at faults. The following general conclusions are drawn from these results: (1) shorts between transistor gate and drain are adequately detected by stuck-at oriented test patterns, and, hence, they do not represent a significant problem in IC testing: (2) the coverage of transistors stuck-open is significantly dependent on the test pattern generation method used; (3) the detectability of bridgings depends strongly on the circuit topology; and (4) the indirect coverage of transistors stuck-on is inadequate, essentially because a large number of them are undetectable. >

Aliasing in signature analysis testing with multiple-input shift-registers

Signature analysis with multiple-input shift registers (MISRs) is often used to realize efficient built-in self-test of digital VLSI circuits. The authors present a statistical theory that explains the dependence of aliasing probability on the main MISR features, such as length and feedback network, and thus makes it possible to prove criteria for the MISR design. The assumption of independent errors at the register inputs is used to model the register behavior as a Markov process, whose equations are then solved to obtain the exact dependence of aliasing probability as a function of test length, input error probabilities, and feedback structure.<<ETX>>

On-line Testing of an Off-the-shelf Microprocessor Board for Safety-critical Applications

The paper describes the strategy adopted to implement on-line test procedures for a commercial microprocessor board used in an automated light-metro control system. Special care has been devoted to chose the most effective test strategy for memory elements, processors, and caches, while guaranteeing a minimum impact on the normal behavior of the whole system. Implementation of the described techniques will significantly improve the system ability to safely react to possible faults. This will be quantitatively determined in the subsequent dependability evaluation phase.