Run-Length-Based Test Data Compression Techniques: How Far from Entropy and Power Bounds?—A Survey

Abstract

The run length based coding schemes have been very effective for the test data compression in case of current generation SoCs with a large number of IP cores. The first part of paper presents a survey of the run length based codes. The data compression of any partially specified test data depends upon how the unspecified bits are filled with 1s and 0s. In the second part of the paper, the five different approaches for “don't care” bit filling based on nature of runs are proposed to predict the maximum compression based on entropy. Here the various run length based schemes are compared with maximum data compression limit based on entropy bounds. The actual compressions claimed by the authors are also compared. For various ISCAS circuits, it has been shown that when the X filling is done considering runs of zeros followed by one as well as runs of ones followed by zero (i.e., Extended FDR), it provides the maximum data compression. In third part, it has been shown that the average test power and peak power is minimum when the don't care bits are filled to make the long runs of 0s as well as 1s.