Applications of decorator and observer design patterns in functional verification

This paper explores the applications of decorator and observer design patterns in testbench environments. Decorator pattern is used to avoid class extension, when new responsibilities are to be added to an object. The application is presented for dynamically adding new constraints to an object. It allows creation of a pre-defined set of constraints to be used as a constraint library; whereas coding all possible combinations of constraints can result in sub-class explosion. Similar application is presented for test sequencing, where a combination of sequences/scenarios are dynamically put together to build more complex scenarios. Application of observer pattern is presented to maintain configuration consist in a chip-level testbench, when registers are accessed at runtime. In the proposed technique, re-configuration is self-maintained. A value change in a configuration register is observed by dependent modules and corresponding updates are taken place automatically. The knowledge of dependency is built as modules are attached to an observant subject.