Improving the Functional Test Delay Fault Coverage: A Microprocessor Case Study

Functional test guarantees that the circuit is tested under normal conditions, thus avoiding any over-as well as under-test issues. This work is based on the use of Software-Based-Self-Test that allows a special application of functional test to the processor-based systems. This strategy applies the so-called functional test programs that are executed by the processor to guarantee a given fault coverage. The main goal of this paper is to investigate a methodology to improve the delay fault coverage of a given test set of functional test programs. We propose to exploit existing Design-for-Test architecture to apply in a smarter way the functional programs. Then, we combine those programs with the classical at-speed LOC and LOS delay fault testing schemes to further increase the delay fault coverage. Results show that it is possible to achieve a global test solution able to maximize the delay fault coverage.