enVision: the inside story

It is pointed out that two long-standing concerns of device test engineers have been run-time efficiency and ease of modification. Traditionally test languages optimizing one have sacrificed the other. The author examines the implementation of the enVision visual test programming language from this perspective. In analyzing the nature of a test program from an implementation perspective, four components are recognized: flow control, static background, dynamic background, and executable statements. The dynamic background component must optimize both run-time efficiency and flexibility and is therefore a critical component in implementing enVision. The information flow from specification sheet through timing equations and into the tester registers may be represented as a DAG (directed acyclic graph). It is noted that the nature of DAGs allows certain significant optimization to be achieved