HTDD based parallel fault simulator

Fault simulation for synchronous sequential circuits is a very time-consuming task. The complexity of the task increases if there is no information about the initial state of the circuit. In this case an unknown initial state is assumed which is usually handled by introducing a three-valued logic. As it is well-known fault simulation based on this logic only determines a lower bound of the fault coverage. Recently it has been shown that fault simulation based on the multiple observation time test strategy can improve the accuracy of the fault coverage. In this paper we describe how this strategy can be successfully implemented based on Ordered Binary Decision Diagrams. Our experiments demonstrate the efficiency of the fault simulation procedure developed.

VISION is an efficient parallel pattern fault simulator for synchronous sequential circuits. VISION is based on an earlier fault simulator called PARIS which was the first and a highly efficient parallel pattern fault simulator. In this paper, we propose four new heuristics which substantially speed up the parallel pattern fault simulation for synchronous sequential circuits. According to our experiments, our fault simulator, VISION, which incorporates the four heuristics, is about 1.6 times faster than PARIS for 16 benchmark circuits.

In this paper, a time and memory-efficient diagnostic fault simulator for sequential circuits is first presented. A distributed diagnostic fault simulator is then presented based on the sequential algorithm to improve the speed of the diagnostic process. In the sequential diagnostic fault simulator, the number of fault-pair output response comparisons has been minimized by using an indistinguishability fault list that stores the faults that are indistinguishable from each fault. Due to the symmetrical relationship of the fault-pair distinguishability, fault list sizes are reduced. Therefore, the different diagnostic measures of a given test set can be generated very quickly using a small amount of memory. To further speed up the process of finding the indistinguishable fault list for each fault, a distributed approach is proposed and developed. The major idea for this approach is that each processor constructs the indistinguishable fault lists for a certain percentage of faults only. Experimental results show that the sequential diagnostic fault simulator runs faster and uses less memory than a previously developed one and that the distributed algorithm even achieves superlinear speedup for a very large sequential benchmark circuit, s35932. To the authors' knowledge, no distributed diagnostic fault simulation system for sequential circuits has been proposed before.

The paper describes COMBINED, a super fast fault simulator for synchronous sequential circuits. COMBINED results from coupling a parallel pattern simulator with a nonparallel simulator both working based on single fault propagation. Circuit partitioning and removing all feedback loops implemented into the parallel part of COMBINED result in a reduction of the number of events. In addition, the nonparallel part of COMBINED has been expanded either to detect more faults by introducing restricted symbolic fault simulation, or to reduce the number of events using PStar Algorithm which are also presented. COMBINED runs substantially faster on ISCAS-89 benchmark circuits than a state-of-the-art single fault propagation simulator.

The paper presents a concept of single event equivalence to be used in the sequential circuit fault simulator. The concept dynamically identifies the equivalent faults for a simulated pattern. It combines advantages of the fanout-free region, critical path tracing and the dominator concept, which were applicable only to combinational circuit fault simulation. The implemented fault simulator, SEESIM, based on the concept, demonstrated a performance superior to that of a state-of-the-art concurrent fault simulator, and comparable to that of parallel-pattern single-fault propagation simulators. It requires a minimal amount of memory and, because of its simplicity, can be easily extended to multilogic or higher level simulation.

~ NJ 07974 Abstract - This paper addresses the problem of simukating transition faults in synchronous sequential circuits. After presenting the concept of the transition fault modell for sequential circuits, we present a fault simulation algorithm for transition faults. The algorithm is a modification of PROOFS, a parallel, differential fault simulation algorithm for stuck faults. A novel fault injection technique is pro- posed. Experimental results show that neither a comprehen- sive functional verification sequence nor a test sequence gen- erated by a sequential circuit test generator for stucck-at faults produces a high fault coverage for transition faults. and finite state machine (FSM) synthesis for delay testabil- ity was adtlressedl. A known reset state is required. The method has limited capability of handling large circuits, because it Icquires the extraction of the complete or partial state transition graph. The approach suggested in 1131 assumes that the circuit is fault-free in the initialization and fault propagation phases. This suggestion is valid if the clock is applied alt a lower speed during the initialization and the fault propagation phases and is applied at a rated speed during the fault activation phase. Slow clock for ini- tialization ,and fault propagation is also assumed in (12). To the author's Icnowledge, no delay-fault simulator €or sequential circuits has been reported before. In this paper, we address the problem of simulating transition faults in sequential circuits. We first enhance the transition fault model for the gate-delay faults and the stuck-open faults in synchronous sequential circuits. We assume the input vectors and clock are applied at speed and at a fixed interval during test application. The primary outputs are: also observed at a fixed interval. We use a transition fault of size n clock cycles to model the defects that cause im extra delay of n clock cycles to a transition. We present a fault simulation algorithm for the proposed fault model. Fault simulation results on the ISCAS-89 sequential benchmark circuits are presented in Section 5.

Methods are investigated for reducing events in sequential circuit fault simulation by reducing the number of faults simulated for each test vector. Inactive faults, which are guaranteed to have no effect on the output or the next state, are identified using local information from the fault-free circuit in one technique. In a second technique, the Star-algorithm is extended to handle sequential circuits and provides global information about inactive faults, based on the fault-free circuit state. Both techniques are integrated into the PROOFS synchronous sequential circuit fault simulator. An average 28% reduction in faulty circuit gate evaluations is obtained for the 19 ISCAS-89 benchmark circuits studied using the first technique, and 33% reduction for the two techniques combined. Execution times decrease by an average of 17% when the first technique is used. For the largest circuits, further improvements in execution time are made when the Star-algorithm is included. >

A fast fault simulation approach based on ordinary logic emulation is proposed. The circuit configured into our system that emulates the faulty circuit's behaviour is synthesized from the good circuit and the given fault list in a novel way. Fault injection is made easy by shifting the content of a fault injection scan chain or by selecting the output of a parallel fault injection selector, with which we get rid of the time-consuming bit-stream regeneration process. Experimental results for ISCAS-89 benchmark circuits show that our serial fault emulator is about 20 times faster than HOPE. The speedup grows with the circuit size by our analysis. Two hybrid fault emulation approaches are also proposed. The first reduces the number of faults actually emulated by screening off faults not activated or with short propagation distances before emulation, and by collapsing nonstem faults into their equivalent stem faults. The second reduces the hardware requirement of the fault emulator by incorporating an ordinary fault simulator.

The authors present a new fast fault simulation algorithm using a content addressable memory, which deals with zero-delay fault simulation of gate-level synchronous sequential circuits. The new algorithm attempts to reduce the computation time by processing many faults at a time on the assumption that a content addressable memory can be regarded as a single instruction multiple data (SIMD) type parallel computation machine. According to theoretical estimation, the speed performance of a simulator based on the proposed algorithm is comparable to that of a fast fault simulator implemented on a vector supercomputer for a circuit of about 2400 gates. >

We propose two new asynchronous parallel algorithms for test set partitioned fault simulation. The algorithms are based on a new two-stage approach to parallelizing fault simulation for sequential VLSI circuits in which the test set is partitioned among the available processors. These algorithms provide the same result as the previous synchronous two stage approach. However, due to the dynamic characteristics of these algorithms and due to the fact that there is very minimal redundant work, they run faster than the previous synchronous approach. A theoretical analysis comparing the various algorithms is also given to provide an insight into these algorithms. The implementations were done in MPI and are therefore portable to many parallel platforms. Results are shown for a shared memory multiprocessor.

A fault simulator for large synchronous sequential circuits is presented in this paper. There are four key ideas to the fault simulator. (1) It uses the critical path tracing method to screen out the single event faults that need not map into equivalent stem faults. (2) It uses the single fault propagation method to map the traced single event faults into equivalent stem faults. (3) All the multiple event faults are dynamically ordered for each test pattern such that the faults with the same faulty effects can be put into the same packet, so as to reduce the number of events created during simulation. (4) All the packets are propagated simultaneously; therefore, each gate is simulated only once for each test pattern, and while propagating packets, equivalent stem faults are also inserted into the packets and propagated as well. A memory sharing technique is used to reduce the memory overhead. Experimental results show that our fault simulator runs faster than PROOFS, HOPE, and improved HOPE (HOPE1.1) for large synchronous sequential benchmark circuits.

In this paper we propose a methodology for obtaining a closed form expression for the output of a linear analog circuits from its state-space description. Voltage waveforms at all the nodes of the circuit are obtained as polynomials in time. This closed form expressions for the circuit response together with the adjoint network method and sparse matrix techniques enhances fast parallel fault simulation. Experiments indicate that significant speedup of fault simulation over serial fault simulation using HSPICE can be obtained using our approach.

The authors describe PARIS, a parallel-pattern fault simulator for synchronous sequential circuits. PARIS is based on the well-known approach of parallel pattern single fault propagation for combinational circuits and features several new techniques. Every single pattern packet is simulated by an iterative, event-driven method. Heuristic look-ahead of signal values minimizes the number of events that must be tracked. Clever circuit partitioning prevents multiple evaluation of the feedback free parts of the circuit, thus reducing the required simulation effort. Experiments show that PARIS runs at a substantially higher asymptotic speed compared with a state-of-the-art fault simulator for synchronous sequential circuits. >

A new method for hierarchical fault simulation based on multi-level decision diagrams (DD) is proposed. We suppose that a register transfer (RT) level information along with gate-level descriptions for blocks of the RT level structure are available. Decision diagrams (DDs) are exploited as a uniform model for describing circuits at these representation levels. The approach proposed allows one to reduce time expenses in the comparison to traditional gate-level fault simulation approach.

In this work we describe a diagnostic fault simulator for sequential circuits which evaluates the effectiveness of a given test set in distinguishing between faults. Diagnostic fault simulation is performed on several ISCAS89 sequential benchmark circuits using two diferent deterministic test sets for each circuit. Several diagnostic measures are reported, including the diagnostic resolution, the diagnostic power, and the sizes of the indistinguishable fault classes. In addition, lists of indistinguishable faults are generated. Use of the diagnostic fault simulator to diagnose faults, given the output responses of failing devices, is also described.