Standardized Functional Verification- P6:Every manager who brings a design to tape-out or who purchases IP must eventually face these questions. The ability to answer these questions based on quantitative analysis is both vital and yet elusive. In spite of the enormous technical advances made in IC development and verification software, the answers to these questions are still based largely on guesswork and hand waving. | Special Cases 35 struct gen crc crc int crc compute crc data keep impose error TRUE crc crc 1 Adding 1 to computed value yields a crc error. Generating Excitement Choosing the values of the external conditional variables and the values of stimulus variables determines the excitation of an instance within its context. Pseudo-random excitation is currently the province of commercially available pseudo-random test generators. Special Cases The foregoing categories of variables connectivity activation conditions and stimuli and response form the basis for pseudo-randomly exercising the target. However certain aspects of a target s functionality may not be readily exercised in a pseudo-random manner but instead require special treatment. These are best defined as special cases and are often exercised with deterministic tests or with deterministic test sequences within a pseudorandom sequence. Most special cases will be associated with stimuli or responses but there may also be other things to verify that just don t seem to fit neatly into any subset. This should not impede progress in interpreting the design specifications - just write them down as for later classification. Eventually with time and increasing familiarity with the design special cases in this latter category will be recast as variables of suitable type with their respective ranges. Treating them as special cases early in the project is a practical convenience that enables progress in spite of a few loose ends . Interpreting functionality related to reset often accumulates a number of special cases. For example checking the state of the target immediately after de-assertion of reset whether hard reset or soft reset is more readily accomplished with a deterministic test and merits description as one or 36 Chapter 2 - Analytical Foundation more special cases. Similarly checking for state preservation upon receiving a soft reset constitutes another batch of special cases. On the other hand .
