Wrapper design for embedded core test

Abstract

A wrapper is a thin shell around the core, that provides the switching between functional, and core-internal and core-external test modes. Together with a test access mechanism (TAM), the core test wrapper forms the test access infrastructure to embedded reusable cores. Various company-internal as well as industry-wide standardized but scalable wrappers have been proposed. This paper deals with the design of such core test wrappers. It gives a general architecture for wrappers, and describes how a wrapper can be built up from a library of wrapper cells which are selected on basis of the terminal types of the core. We show that the ordering and partitioning of wrapper cells and core-internal scan chains over TAM chains determine the test time of the core. An heuristic approach for the NP-hard problem of partitioning the TAM chain items for minimal test time is presented and its usage is illustrated by means of an example. Finally we sketch how wrapper generation and verification can be automated.