US Patent 7900111 Method and apparatus for random stimulus generation

Capabilities are added to a Hardware Verification Language that facilitates the generation of test data. Random number sources, called random variables, can be produced by adding a randomness attribute to a variable declaration of a class definition. A “randomize” method call to a class instance produces a random value for each random variable. Constraint blocks, of a class definition, control random variables with constraint expressions. Dependency, of random variable value assignment, as determined by constraint expressions, can be expressed by a DAG. A constraint expression is converted into ranges of permissible values, from which a value is randomly chosen by a randomize method. A “boundary” method call sequentially selects a combination of boundary values, for each random variable, from each random variable's set of ranges. Coordinated selection of a boundary values permits all combinations of boundary values to be produced through successive boundary calls.