Wrapper scan chains balance algorithm base on twice assigned by difference and mean value

The core test application time is based on the maximum scan-in/scan-out chains. To design a well balance wrapper scan chains is an important approach to reduce the test application time and test cost. We propose a wrapper scan chains balance algorithm base on twice-assigned algorithm by the chains difference and mean value. By selecting a standard chain with its length L, calculating the mean value V of all scan chains, then finding the chains which length longer than L from all internal scan chains of the IP core, computing the difference D with V of these chains, the first assignment is achieved by regarding these chains as V. By sorting the length shorter than L and D in descending order of length, the second assignment is achieved by assigning to the enable shortest or longest wrapper scan chain according whether D is positive or negative. The experimental results for the ITC'02 SOC Test Benchmark showed that the algorithm in this paper can get better balanced result when compared to the existing solutions.