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.

A Test Data Compression Method Based on K-L Transform

“…Therefore, the vertical K-L transform is chose to perform in the next experiments. The results in Table 2 show that the proposed method compares with other schemes [7]. Here the length of test vectors and the number of test vectors are omitted.…”

“…For instance, Chandra [4] proposed FDR code to encode the runs of 0s in the test cubes, and Ei-Maleh [5] exhibited EFDR code to encode the runs of 0s and 1s simultaneously, and Liang [6] showed Alt-FDR code to encode the runs of 0s and 1s alternately. However, the existence of entropy limits the test compression [7].…”

Test Data Compression Using Variable Prefix Run Length (VPRL) Code

“…There are many techniques to control the volume of test data, test application time and power consumption in test mode. Test data volume and power reduction can be achieved by utilizing Built-in-Self-test (BIST) [2,3], test data compaction or test data compression techniques [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][20][21][22]. However, BIST requires a longer test application time.…”

“…The objective of test data compression is to reduce the number of bits needed to represent the test data. There exists many test data compression techniques like Broadcast scan-based, Linear decompression based, and Code-based techniques [8,9,19]. Code-based test data compression scheme is more appropriate for larger devices.…”

“…Code-based test data compression scheme is more appropriate for larger devices. Some of the code-based test data compression schemes are Dictionary codes, Statistical codes, Constructive codes, and Run length-based codes are used for test data compression [8,9,19]. Among these, run length-based codes are used to encode the repeatedly occurring values and is an efficient method for test data compression.…”