TEST DATA COMPRESSION USING BITMASK & DICTIONARY SELECTION METHODS

ABSTRACT The objective of the project is that it proposes a test compression technique using efficient dictionary and bitmask selection to significantly reduce the testing time and memory requirements.It provides improvement in compression efficiency without introducing any penalty for decompression.

COMPRESSION compression

Lossy compression Lossless compressionLossy: The compression through which replication of original data is not required. Eg: compression of graphic images ,digitised voice.Lossless: The compression after which the original data can be extracted ,means replication of original is essential. Eg: compression of database records , spreadsheetsHere our proposed approach is an lossless compression ,here the original is replicated from the compressed one.

WHATS NEED TO COMPRESS TEST DATA? Higher Circuit Densities in SOC

Large Test Data Volume

Higher Memory Requirements

Increase in Testing Time.

TEST DATA COMPRESSION

TEST DATA COMPRESSION METHODOLOGYUNCOMPESSED TEST DATADECOMPRESSION HARDWARECOMRESSED TEST DATA

(MEMORY)DESIGN UNDER TEST

(DUT)COMPRESSION ALGORITHM

METHODS FOR DATA COMPRESSION Bitmask-based Test data compression: This method provides the number and type of profitable bitmasks. By using this method a large extent of test vectors can be compressed.Dictionary Selection method: This algorithm generates the Dictionary Methods try to replace a symbol or group of symbols by a dictionary location code. Some dictionary-based techniques use simple uniform binary codes to process the information supplied e dictionary entries.

COMPRESSION ALGORITHMInputs: Test DataDivide test data based on scan chainsSelect bitmasksPerform dictionary selectionCompress using selected dictionary & bitmasksOutput: Compressed Test Data and Dictionary

DECOMPRESSION:

The decompression engine takes the compressed vectors input. It checks the first bit to see whether the data is compressed or not.If the first bit is 1, it directly sends the uncompressed data to the output buffer. On the other hand, if the first bit is a 0, it implies this is a compressed data. Now, there are two possibilities in this scenario. The data maybe compressed directly using dictionary entry or may have used bitmasks.

DECOMPRESSION METHODOLOGY

REQUIREMENTS:Software being used: XILINX ISE Language used: VHDL/verilogSimulated by xilinx

CONCLUSIONOur algorithm outperforms existing dictionary based compression by up to 30%, giving a best possible compression of 92%. Our approach also generates up to 60% improvement in compression efficiency compared to bitmask-based compression without introducing any additional performance or area overhead.

REFERENCESS. Seong and P. Mishra, Bitmask-based code compression for embedded systems, IEEE Trans. Comput.-Aided Des. Integr. CircuitsSyst., vol. 27, no. 4, pp. 673685, Apr. 2008L. Li, K. Chakrabarty, and N. Touba, Test data compression using dictionaries with selective entries and fixed-length indices, ACM Trans. N. Touba and E. McCluskey, Altering a pseudo-random bit sequence for scan based bist, in Proc. Int. Test Conf., 1996, pp. 167175. Des. Autom. Electron. Syst., vol. 8, no. 4, pp. 470490, 2003.

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