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Spectral RTL Test Generation for Gate-Level Stuck-at Faults

Spectral RTL Test Generation for Gate-Level Stuck-at Faults. Nitin Yogi and Vishwani D. Agrawal Auburn University, Department of ECE, Auburn, AL 36849, USA. Outline. Need for High Level Testing Problem and Approach Spectral analysis and test generation RTL testing approach

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Spectral RTL Test Generation for Gate-Level Stuck-at Faults

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  1. Spectral RTL Test Generation for Gate-Level Stuck-at Faults Nitin Yogi and Vishwani D. Agrawal Auburn University, Department of ECE, Auburn, AL 36849, USA ATS'06

  2. Outline • Need for High Level Testing • Problem and Approach • Spectral analysis and test generation • RTL testing approach • Experimental Results • Conclusion ATS'06

  3. Need for High Level Testing • Motivations for high level testing: • Reduced test generation complexity • Reduced time and cost for test development • Early resolution of testability issues • Difficulty of gate-level test generation for black box cores with known functionality ATS'06

  4. Problem and Approach • The problem is … • Develop an effective RTL ATPG method • And our approach is: • Implementation-independent characterization: • RTL test generation • Spectral analysis of RTL vectors • Test generated to cover faults in gate-level implementation: • Generation of spectral vectors • Fault simulation and vector compaction ATS'06

  5. Faults Modeled for an RTL Module CombinationalLogic Inputs Outputs RTL stuck-at fault sites FF FF A circuit is an interconnect of several RTL modules. ATS'06

  6. Spectral Characterization of a Digital Bit-Stream w0 • Walsh functions: a complete orthogonal set of basis functions that can represent any arbitrary bit-stream. • Walsh functions form the rows of a Hadamard matrix. w1 w2 w3 Walsh functions (order 8) H8 = 1 1 1 1 1 1 1 1 1 -1 1 -1 1 -1 1 -1 1 1 -1 -1 1 1 -1 -1 1 -1 -1 1 1 -1 -1 1 1 1 1 1 -1 -1 -1 -1 1 -1 1 -1 -1 1 -1 1 1 1 -1 -1 -1 -1 1 1 1 -1 -1 1 -1 1 1 -1 w4 w5 w6 w7 Example of Hadamard matrix of order 8 time ATS'06

  7. Walsh Coefficients of a Bit-Stream • A bit-stream is correlated with each row of Hadamard matrix. • Highly correlated basis functions => retained as essential components Others => noise. Bit stream to analyze Correlating with Walsh functions by multiplying with Hadamard matrix. Bit stream Spectral coeffs. Essential component (others noise) Hadamard Matrix ATS'06

  8. Bit-Stream Generation • New spectrums are generated retaining essential components and adding random noise. • New spectrums are converted into bit-streams by multiplying with Hadamard matrix. • Any number of bit-streams can be generated; All contain the same essential components but differ in noise Perturbation New spectrum Original spectrum Bits changed multiplying with Hadamard matrix Essential component retained New bit-stream ATS'06

  9. RTL Testing Approach (Circuit Characterization) • RTL test generation: • Test vectors generated for RTL faults (PIs, POs and inputs - outputs of RTL modules and flip-flops.) • Spectral analysis: • Test sequences for each input bit-stream are analyzed using Hadamard matrix. • Amount of perturbation is determined by a gradually increasing noise level. ATS'06

  10. Power Spectrum: “Interrupt” Signal PARWAN Processor Circuit Essential components Noise components Normalized Power Randomlevel(1/128) Spectral Coefficients ATS'06

  11. Power Spectrum: “Ready” Signal PARWAN Processor Circuit Examples of Essential components Normalized Power Examples of Noise components Randomlevel(1/128) Spectral Coefficients ATS'06

  12. Power Spectrum: “DataIn[5]” Signal PARWAN Processor Circuit Examples of Essential components Examples of Noise components Normalized Power Randomlevel(1/128) Spectral Coefficients ATS'06

  13. Power Spectrum: A Random Signal Normalized Power Averagelevel(1/128) Spectral Coefficients ATS'06

  14. Selecting Minimal Vector Sequences Using ILP • Fault simulation of new sequences • A set of perturbation vector sequences {V1, V2, .. , VM} are generated. • Vector sequences are fault simulated and faults detected by each is obtained. • Compaction problem • Find minimum set of vector sequences which cover all the detected faults. • Minimize Count{V1, … ,VM} to obtain compressed seq. {V1,… ,VC} where {V1, … ,VC}{V1, … , VM}Fault Coverage{V1, … ,VC} = Fault Coverage{V1, … ,VM} • Compaction problem is formulated as an Integer Linear Program (ILP) [1]. [1] P. Drineas and Y. Makris, “Independent Test Sequence Compaction through Integer Programming," Proc. ICCD’03, pp. 380-386. ATS'06

  15. Results: Circuit Characteristics • RTL Spectral ATPG technique applied to the following benchmarks: • 4 ITC’99 high level RTL circuits • 4 ISCAS’89 circuits. • PARWAN processor(Z. Navabi, VHDL: Analysis and Modeling of Digital Systems, McGraw-Hill, 1993.) • Characteristics of benchmark circuits: • ATPG for RTL faults and fault simulation performed using commercial sequential ATPG tool Mentor Graphics FlexTest. • Results obtained on Sun Ultra 5 machines with 256MB RAM. ATS'06

  16. Results for b11-A** RTL characterization: RTL-ATPG results: * Sun Ultra 5, 256MB RAM ** Area-optimized synthesis in Mentor’s Leonardo ATS'06

  17. b11-A Circuit ATS'06

  18. PARWAN processor ATS'06

  19. Results * Reset input added. ATS'06

  20. Conclusion • Spectral RTL ATPG technique applied to ITC’99 andISCAS’89 benchmarks, and a processor circuit. • Vectors generated for RTL faults were spectrally analyzed and new vectors generated through perturbation. • In most cases, Spectral RTL ATPG gave similar or better test coverage in shorter CPU time as compared to sequential ATPG • Test generation using Spectral RTL ATPG brings with it the benefits of high level testing • Techniques that will enhance Spectral ATPG are: • Efficient RTL ATPG • Accurate determination and use of noise components • Better compaction algorithms ATS'06

  21. Thank You ! Questions ? ATS'06

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