Addressing Useless Test Data in Core-Based System-on-a-Chip Test

This paper analyzes the test memory requirements for core-based systems-on-a-chips and identifies useless test data as one of the contributors to the total amount of test data. The useless test data com-prises the padding bits necessary to compensate for the difference between the lengths of different chains in multiple scan chains designs. Although useless test data does not represent any relevant test informa-tion, it is often unavoidable, and it leads to the trade-off between the test bus width and the volume of test data in multiple scan chains-based cores. Ultimately this trade-off influences the test access mechanism design algorithms leading to solutions that have either short test time or low volume of test data. There-fore, in this paper, a novel test methodology is proposed, which by dividing the wrapper scan chains into two or more partitions, and by exploiting automated test equipment memory management features re-duces the useless memory. Extensive experimental results using ISCAS89 and ITC02 benchmark circuits are provided to analyze the implications of the number of wrapper scan chains in the partition, and the number of partitions on the proposed methodology