R.C. Ho and M.A. Horowitz. Validation coverage analysis for complex digital designs. In International Conference on Computer Aided Design, pages 146--151, November 1996. 16  Home/Search   Document Not in Database   Summary   Related Articles   Check

....as that of formally verifying the entire design. It may be possible for the designer to suggest how to perform the expansion, but then the procedure is no longer automatic. 2.3 Coverage estimation This research is aimed at evaluating the effectiveness of an existing set of tests. The authors of [15, 17] operate on designs which can be split into control and datapath. An abstract representation of the controller is built, and it is determined which edges in the STG of the controller are excited by the test suite applied to the design. In this way, the designer may discover that certain important ....

Ho, R. and M. Horowitz: 1996, `Validation Coverage Analysis for Complex Digital Designs'. In: Proc. Intl. Conf. on Computer-Aided Design.

....cation. This direction, of checking whether the speci cation describes the system exhaustively, has roots in simulation based veri cation techniques, where coverage metrics are used in order to reveal states that were not visited during the testing procedure (i. e, not covered by this procedure) [HMA95, HYHD95, DGK96, HH96, KN96, FDK98, MAH98, BH99, FAD99]. For example, code coverage [CK93] measures the fraction of HDL statements executed during simulation, transition coverage [HYHD95, HMA95] measures the fraction of transitions executed, and tag coverage [DGK96] attributes variables with tags that are used to detect whether assigning a forbidden ....

....FAD99] Fallah et al. compute the tag coverage achieved by simulation and generated simulation sequences that cover a given tagged variable. Of a similar nature is the tour generation algorithm in [HYHD95] which generates test vectors that traverse all states of the system. Ho and Horowitz [HH96] de ne test coverage in terms of control events. Each control event identi es an 1 interesting subset of the control variables, and the test vectors have to cover all the events. They also de ne design coverage by means of the states and edges covered by the test vectors (see also [MAH98] In ....

R.C. Ho and M.A. Horowitz. Validation coverage analysis for complex digital designs. In International Conference on Computer Aided Design, pages 146-151, November 1996.

....tests. He found that designers presented with state transitions that were not covered had great difficulty generating tests to exercise these transitions. An automated method for test generation would have helped a lot. This direction of research set in [Ho95] has gained considerable following: [Ho96b, Ho96a, Geis96, Gupt97, Lewi96, Moun98]. Of particular interest is a study of the relationship between reduced FSM coverage and design error coverage by Gupta et al. Gupt97] However, theoretical results in this area tend to be weak and extensive experimental studies have not appeared in the literature. Design specific coverage ....

....proven automatically using induction on the number of execution cycles. To achieve the high degree of automation, the approach of [Levi97] uses high level knowledge about the design, such as the design intent of a bypass. Hybrid verification techniques A class of hybrid verification techniques [Geis96, Gupt97, Ho95, Ho96b, Lewi96, Moun98] that combine simulation with formal verification has recently been proposed. These techniques construct a reduced FSM model of the implementation. Test sequences are then generated to achieve full coverage on the reduced FSM model. A non trivial 1. A k definite FSM is one that can only remember ....

R. C. Ho and M. A. Horowitz. Validation coverage analysis for complex digital designs. In Proc. Int. Conf. Computer-Aided Design, pages 146--151, 1996.

....such as existing application and system software [20] These test generation techniques are used in conjunction with coverage metrics to quantify the effectiveness of a verification test suite. The metrics include code coverage metrics from software testing [5] finite state machine coverage [15], architectural event coverage [27] and observability based metrics [10] A shortcoming of all these metrics is that the relationship between the metric and the detection of classes of design errors is not well specified or understood. An alternative verification approach draws on the ....

....is proven automatically using induction on the number of execution cycles. To achieve the high degree of automation, the approach of [23] uses high level knowledge about the design, such as the design intent of a bypass. D. Hybrid verification techniques A class of hybrid verification techniques [11, 13, 15, 24, 25] that combine simulation with formal verification has recently been proposed. These techniques construct a reduced FSM model of the implementation. A test set is generated that achieves full coverage on the reduced FSM 1. A k definite FSM is one that can only remember the last k inputs. 3 of 8 ....

R. C. Ho and M. A. Horowitz. "Validation coverage analysis for complex digital designs." In Proc. Int. Conf. CAD, 1996, pp. 146-- 151.

....as that of formally verifying the entire design. It may be possible for the designer to suggest how to perform the expansion, but then the procedure is no longer automatic. 2.3 Coverage estimation This research is aimed at evaluating the effectiveness of an existing set of tests. The authors of [15, 17] operate on designs which can be split into control and datapath. An abstract representation of the controller is built, and it is determined which edges in the STG of the controller are excited by the test suite applied to the design. In this way, the designer may discover that certain important ....

R. Ho and M. Horowitz. Validation Coverage Analysis for Complex Digital Designs. In Proc. Intl. Conf. on ComputerAided Design, November 1996.

....a given test the safety property is violated, the corresponding monitor enters a violation state, agging the failure. E ectiveness of simulation sequences is assessed using several coverage metrics: code coverage [86, 32, 33] tag coverage [35] event coverage [48] and state machine coverage [70, 53, 51, 52]. Code based coverage includes statements, branch and path coverage. Tag coverage evaluates the observability of possible incorrect evaluation represented as tags at the circuit outputs. Event coverage is measured by activating the coverage models on the event trace. State machine coverage is ....

....expansion is as high as that of formally verifying the entire design. It may be possible to manually spell out the expansion step, but then the procedure is no longer automatic. Coverage estimation This research is aimed at evaluating the e ectiveness of an existing set of tests. The authors of [51, 53] operate on designs which are split into control and datapath. An 75 abstract representation of the controller is built, and it is determined which edges of the State Transition Graph (STG) of the controller are excited by the veri cation test suite applied to the design. In this way, the ....

R. Ho and M. Horowitz. Validation Coverage Analysis for Complex Digital Designs. In Proc. Intl. Conf. on Computer-Aided Design, November 1996.

....specification also escapes the attention of the designer, who is often the one to provide the specification. In simulation based verification techniques, coverage metrics are used in order to reveal states that were not visited during the testing procedure (i. e, not covered by this procedure) [HMA95,HYHD95,DGK96,HH96,KN96,FDK98,MAH98,BH99,FAD99]. These metrics are a useful way of measuring progress of the verification process. However, the same intuition cannot be applied to model checking because the process of model checking visits all states. We can say that in testing, a state is uncovered if it is not essential to the success of ....

R.C. Ho and M.A. Horowitz. Validation coverage analysis for complex digital designs. In Proc 8th CAD, pp. 146--151, November 1996.

....is as high as that of formally verifying the entire design. It may be possible to manually spell out the expansion step, but then the procedure is no longer automatic. 1.1.3 Coverage estimation This research is aimed at evaluating the effectiveness of an existing set of tests. The authors of [12, 14] operate on designs that are split into control and datapath depending on the user specified annotations of control and data registers. An abstract representation of the controller is built, and it is 4 determined which edges in the STG of the controller are excited by the verification test suite ....

....1; D; D; Xg calculus used for fault simulation. They make the important point that bugs need to be both excited as well as made visible. 1.1. 4 Conservative approximations Several authors have elected to work with sacrificing FV in the other direction, i.e. they never report false positives [12, 14, 17, 18]. A simple view of these papers is that they approximate the design and build an overestimate of the set of reachable states. Consequently, if the tools reports that the design satisfies the specified invariants, it really does so. However, there is the problem of false negatives: checking that ....

R. Ho and M. Horowitz. Validation Coverage Analysis for Complex Digital Designs. In Proc. Intl. Conf. on Computer-Aided Design, November 1996.

....[FDK98,FAD99] Fallah et al. compute the tag coverage achieved by simulation and generated simulation sequences that cover a given tagged variable. Of a similar nature is the tour generation algorithm in [HYHD95] which generates test vectors that traverse all states of the system. Ho and Horowitz [HH96] define test coverage in terms of control events. Each control event identifies an interesting subset of the control variables, and the test vectors have to cover all the events. They also define design coverage by means of the states and edges covered by the test vectors (see also [MAH98] In ....

R.C. Ho and M.A. Horowitz. Validation coverage analysis for complex digital designs. In Proc. CAD, pp. 146--151, 1996.

....and so allows larger circuits to be simulated over more cycles. Approximation is widely used in model checking. There are basically two types used. In one method, an exact model is used, but the state space is approximated to keep BDD sizes down [4, 8] Another way is to abstract the model itself [9, 13, 7]. The latter method is often used to extract tests for simulation to increase state coverage. These methods all have the problem that they do not scale to large designs easily, they require a lot of work and expertise, and the abstraction often hides many bugs. Another model checking method uses ....

R. Ho and M. Horowitz. Validation coverage analysis for complex digital designs. In 1996 IEEE International Conference on Computer-Aided Design, pages 146--151, 1996.

....is as high as that of formally verifying the entire design. It may be possible to manually spell out the expansion step, but then the procedure is no longer automatic. 1.1.3 Coverage estimation This research is aimed at evaluating the effectiveness of an existing set of tests. The authors of [12, 14] operate on designs which can be split into control and datapath. An abstract representation of the controller is built, and it is determined which edges in the STG of the controller are excited by the verification test suite applied to the design. In this way, the designer may discover that ....

R. Ho and M. Horowitz. Validation Coverage Analysis for Complex Digital Designs. In Proc. Intl. Conf. on Computer-Aided Design, November 1996.

....microprocessors still rely heavily on simulation based methods to verify their products. An important issue is that of quantifying the effectiveness of these methods. A variety of coverage metrics have been proposed: code coverage from software testing [2, 16] finite state machine based metrics [10, 9, 7, 13], an observability based metric [5, 6] and design specific metrics such as architectural events [12, 14] A shortcoming of these metrics is that the relationship between a metric and the classes of design errors that they detect is not well understood. An alternative approach draws on the ....

R. C. Ho and M. A. Horowitz. "Validation coverage analysis for complex digital designs." In Proc. Int. Conf. Computer-Aided Design, 1996, pp. 146--151.

....need testing and which have been tested. One possible approach is to use reachability analysis, or state space enumeration, to quantify the interactions in the control logic of a design. This would provide a definitive and meaningful measure of validation progress. This was done in [HMA95] and [HH96]. In [HMA95] the basic technique is described which extracts the control FSMs from an RTL description. Coverage is then measured in terms of arc coverage of the global control FSM, which is found by symbolic reachability analysis. This provides a comprehensive coverage metric of all the ....

....Coverage is then measured in terms of arc coverage of the global control FSM, which is found by symbolic reachability analysis. This provides a comprehensive coverage metric of all the interactions in a design, as will be described in Chapter 3. However, when applied to large designs as in [HH96], this metric turns out to be too conservative. In order to achieve good coverage numbers on this metric, a redundant number of tests need to be simulated. This dilutes the quality of the metric and makes the validation task unnecessarily lengthy. Instead, the common practical implementation of ....

Richard C. Ho and Mark A. Horowitz, "Validation Coverage Analysis for Complex Digital Designs", In Proceedings of the International Conference on Computer Aided Design, San Jose, California, November 1996.

....The first is toggle coverage, which tells the designer which signals in the design did not take on both a one and a zero value. The diagnostics in the FLASH regression suite toggle almost 100 of the signals in the design. The second hardware verification technique that we used was state coverage [HH96]. Whereas toggle coverage looks at each signal in isolation, state coverage looks at each state machine in the design, and makes sure that all possible states have been reached. The first goal is to make sure that each state machine reaches each of its possible states, and takes each of its ....

Richard C. Ho and Mark A. Horowitz. Validation Coverage Analysis for Complex Digital Designs. To appear in Proceedings of the IEEE/ACM International Conference on CAD, San Jose, CA, November 1996.

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R.C. Ho and M.A. Horowitz. Validation coverage analysis for complex digital designs. In International Conference on Computer Aided Design, pages 146--151, November 1996. 16

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Richard Ho and Mark Horowitz. Validation coverage analysis for complex digital designs. In 1996.

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