An Arithmetic Structure for Test DatAn Arithmetic Structure for Test Data Horizontal Compressiona Horizontal Compression

Marie-Lise FLOTTES, Regis POIRIER, Bruno ROUZEYRE Marie-Lise FLOTTES, Regis POIRIER, Bruno ROUZEYRE Laboratoire d’Informatique, de Robotique et de MicroelectroniLaboratoire d’Informatique, de Robotique et de Microelectroni

que de Montpellier, Franceque de Montpellier, FranceDATE ‘04DATE ‘04

Laboratory of Reliable ComputingDepartment of Electrical EngineeringNational Tsing Hua UniversityHsinchu, Taiwan

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ReferenceReference An Arithmetic Structure for Test Data Horizontal C

ompressionMarie-Lise FLOTTES, Regis POIRIER, Bruno ROUZEYRE

DATE ‘04

Test Data Compression Using Dictionaries with Fixed-Length Indices

Lei Li and Krishnendu ChakrabartyVTS ‘03

An Efficient Test Vector Compression Scheme Using Selective Huffman Coding

Abhijit Jas, Jayabrata Ghosh-Dastidar, Mon-Eng Ng and Nur A. Touba IEEE Transaction on CAD of IC and System, June 2003

Improving compression ratio, area overhead, and test application time for SOC test data compression / decompression

P. T. Gonciari, B. Al-Hashimi and N.Nicolici DAT ‘02

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OutlineOutline

Instruction

Lossless Compression algorithm

Compression principle and De-compressor Architecture

Main Issue Compression Issue Timing Issue

Experimental Result

Compare & Conclusion

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Why need compression ?Why need compression ?

Higher circuit densities and a large number of embedded cores will lead the increase of test data volume, which in turn leads to an increase in testing time.

Transmitting test patterns and handshaking between cores and ATE will waste a lot testing time.

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How to reduce testing cost ?How to reduce testing cost ? ATE has limited pin counts and testing time is

equal to the testing cost.

More patterns transmit to core, more testing time

Reduce testing cost

a. Reduce testing time

- compaction

b. Reduce testing pin counts

- compressionn

m

Channel

n < m

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Compression MethodCompression Method

(1) Easy compression → Hard decompression (2) Hard compression → Easy decompression Compression Method

Lossless Lossy

Compression can be executed through software, therefore the dominate area overhead is the circuit of decompression.

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Lossless Compression AlgorithmLossless Compression Algorithm

Run-Length Coding

Frequency-Directed Run-Length (FDR)

& Extend FDR

Huffman

Dictionary Based

Main idea of above algorithms More common data, shorter bits to represent

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Run-Length CodingRun-Length Coding First bit represents the

data is ‘1’ or ‘0’.

Next m bits represent the runs of ‘1’ or ‘0’.

16 2

24 3

111111000000011111100000

m=3

1110011111100011

101010

m=3

100100011001000110010001

Compression Ratio :24

46

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FDR & EFDRFDR & EFDR

Source : VTS ‘99

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Example of Huffman TreeExample of Huffman Tree

Source : VTS ‘99

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Simplified Huffman TreeSimplified Huffman Tree

Source : vlsitsa ‘01

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Variable-Length Input Variable-Length Input Huffman CompressionHuffman Compression

Source :DAT ‘02

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ExampleExample

12

14

8

1 3 7

1115 4

52

13

16 10

9 6

Source : VTS ‘03

11100011

01000110

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Example(1/2)Example(1/2)

1 3 7

111512 4

528

14 13

16 10

9 6

11

52

13

16

9 6

maximum degree

Sub graph

52

13

16

9 6

5

13

16

6

Clique

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Example(2/2)Example(2/2)

1 3 7

111512 4

528

14 13

16 10

9 6

5

13

16

6

More this clique

1 3 7

111512 4

28

14

10

9

New Graph

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Example ResultExample Result

Obtain 4 cliques ： {5,6,13,16} , {2,8,14} , {3,4,7} , {1,11} 12 words are encoded, and there are else 4 diffe

rent words un-coded. So total need transmit (1+2)*12+(1+8)*4=72 bits. If no compression, we need transmit 8*16=128

bits. Therefore, after compression, reducing about 43.75% bits needed to transmit to core.

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Parameter DefinitionParameter Definition M : # of ATE channel N : # of scan chains in CUT F : # of FF in each scan chain Initial test sequence { V1, V2, … } Numerous difference Di

Di = Vi+1-Vi

Source : DATE ‘04

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M-to-N Horizontal De-compressorM-to-N Horizontal De-compressor

Source : DATE ‘04

M pins in ATE

N scan chains in CUT

M < N

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De-compressor StructureDe-compressor Structure

Source : DATE ‘04

Overhead Adder N bits-M SRA Shifts Reg./Accumulator

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SRA Operation ModeSRA Operation Mode Parallel Mode ( Shift =0 )

Parallel data-in from adder Transfer test pattern to scan chains in CUT

Semi-Parallel Mode ( Shift =1 ) Store test pattern from ATE SRA likes many scan chains

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5bits-3 SRA5bits-3 SRA

Source : DATE ‘04

Test Time Evaluate Parallel mode

One clock cycle Semi-Parallel mode

clock cycleN

M

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Shift-in Test PatternShift-in Test Pattern M test pins in ATE

Max difference is 2M

Compressible pattern & Un-compressible pattern

Compressible pattern shift-in time

Un-compressible pattern shift-in time

NF

M

NF

M

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Compression IssueCompression Issue

2 maxlogM D Reduce Dmax can reduce # of test pins M Importance : MSB > LSB

Source : DATE ‘04

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Compression Issue with Don’t CareCompression Issue with Don’t Care Don’t care bit (X) can be 1 or 0

More don’t care bits, higher compression ratio

Vk0: 1 0 1 x 0Vk1: 0 x x 1 0Vk2: x x 1 x xVk3: 1 x 0 x xVk4: 0 x 1 x 0

1 4 1 4 2

Vk0: x 0 0 1 1Vk1: 1 x 0 x 0Vk2: x x x 1 xVk3: x x x 0 1Vk4: x x 0 1 0

4 4 2 1 1

Vk0: 1 0 0 1 1Vk1: 1 1 0 1 0Vk2: 1 1 1 1 1Vk3: 0 0 1 0 1Vk4: 0 1 0 1 0

Dk0: 0 0 1 1 1Dk1: 0 0 1 0 1Dk2: 0 0 1 1 0Dk3: 0 0 1 0 1

3 bits

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Timing IssueTiming Issue Test pattern transmit time

Total :

Larger Pcomp, smaller test pattern transmit time

Test pattern transmit time is shorter

uncomp uncomp

NT P F

M

( ) 1comp comp

NT P F

M

uncomp compT T F

0 ( ) 1 ( ) 0all all

N NP F F T P F F

M M

( ) classic

NF T

M

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Experimental Results (1)Experimental Results (1)

Source : DATE ‘04

ISCAS89 Benchmark

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Experimental Results (2)Experimental Results (2)

ISCAS89 Benchmark : S9234 Version 1 6 scan chains & Length 42 Version 2 10 scan chains & Length 25 Version 3 10 scan chains & Length 25 6-to-10 compressor

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Experimental Results (3)Experimental Results (3)

Source : DATE ‘04

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ConclusionConclusion

A useful & simple method for reducing test pin A low overhead

Adder & Nbits-M SRA No impact the fault coverage

compressible & un-compressible pattern

Problem Not use the don’t care bit adequately

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Conclusion (cont.)Conclusion (cont.)

Combine the SRA and 1st scan chain

…

Scan chain

SRA…

Scan chain

SRA

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CombinationCombination

Combine this approach with dictionary based compression

1 3 7

111512 4

528

14 13

16 10

9 6

Dictionary Based Compression

Arithmetic Compression

Grouped pattern

Compressed Pattern

Un-compressed Pattern