Title: Abstract timing verification for synchronous digital systems
Abstract: ATV, the Abstract Timing Verifier, is a program to perform static timing analysis of dependency graphs derived from logic designs, analyzing worst-case paths. Unlike other timing verifiers, ATV uses an abstract representation of time and delays that enables a user to choose the representation of time and delays used in the analysis. Such representations include single numbers, ranges (min-max), and statistical descriptions (mean and standard deviation), or asymmetric rise/fall versions of all of these. The sophisticated user may develop new models and plug them in to the program.
ATV uses a new algorithm to analyze critical paths that extend through transparent latches and stretch over multiple machine cycles. By placing events in different reference frames that are rigidly translated relative to one another, the program can be used either to check a design for timing errors when the clock schedule is fixed and known, or to derive spacing constraints between clock edges when only the relative ordering of the clock edges is known.
By defining coercions between delay formats, the same raw data can be analyzed using several different timing models to determine the sensitivity of reported results to the assumptions made by the different models. In one analysis of a chip implementing the Data Encryption Standard, six different timing models reported as many as 14 and as few as 4 critical paths generating the same key event. In general, asymmetric rise/fall models generated more critical paths because of interactions between reconvergent paths of opposite polarity. As expected, min-max models tended to be the most conservative in estimating required cycle times, single-number models using nominal values were the most optimistic, and probabilistic models were in between.
ATV is designed to operate on generic dependency information that could be available early in the design cycle, providing early feedback about the timing implications of microarchitectural decisions. The framework it provides allows new timing models to be developed and compared with existing models on an equal basis. The development of the abstract timing model has led to new understandings of the similarities and differences between the many different timing models in use today.
Publication Year: 1988
Publication Date: 1988-01-01
Language: en
Type: article
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Cited By Count: 6
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