1. March 8, 2006Spectral RTL ATPG1 High-Level Spectral ATPG for Gate-level Circuits Nitin Yogi and Vishwani D. Agrawal Auburn University Department of ECE Auburn, AL 36849

2. March 8, 2006Spectral RTL ATPG2 Outline Need for High Level Testing Problem and Approach Spectral analysis and generation of test sequences RTL testing approach Experimental Results Conclusion Future work Research Goals

3. March 8, 2006Spectral RTL ATPG3 Need for High Level Testing Motivations for high level testing: –Low testing complexity –Low testing times and costs –Early detection of testability issues during design phase at high level or RTL –Difficulty of gate-level test generation for black box cores with known functionality Seems interesting ! But is it feasible ?

4. March 8, 2006Spectral RTL ATPG4 Problem and Approach What’s the problem ? –Develop synthesis-independent ATPG methods using RTL circuit description. How do we approach it ? –Implementation-independent characterization: RTL test generation –RTL faults => PI, PO and inputs and outputs of flip-flops –Generate vectors for RTL faults Analyze RTL vectors to extract spectral components and the noise level for each PI of the circuit. –Test generation for a gate-level implementation using RTL characterization: Generation of test vectors Test vector compaction That’s fine ! But does it work ?

5. March 8, 2006Spectral RTL ATPG5 Walsh Functions and Hadamard Spectrum 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 H 8 = w0w0 w1w1 w2w2 w3w3 w4w4 w5w5 w6w6 w7w7 Walsh functions (order 8) Walsh functions form an orthogonal and complete set of functions representing a discretized function. Walsh functions form the rows of the Hadamard matrix; called its basis vectors. Example of Hadamard matrix of order 8: OK…so its just another way of representing information

6. March 8, 2006Spectral RTL ATPG6 Analysis of a Bit Stream Using Hadamard Matrix Bit stream is correlated with each basis vector of the Hadamard matrix. High correlated basis vectors are retained as essential components and others are regarded as noise. New bit streams can be generated keeping the essential components and eliminating or changing the noise components. Bit stream to analyze Correlating with basis vectors by multiplying with Hadamard matrix. Essential component (others noise) Hadamard Matrix Bit stream Spectral coeffs.

7. March 8, 2006Spectral RTL ATPG7 Test Vector Generation The components regarded as noise are filtered or altered as per a methodology. The filtered components are converted back to a test vector by multiplying with Hadamard matrix Filtering Generation of test vectors by multiplying with Hadamard matrix Spectral components Essential component retained New test vector OK…so you are refining the bit stream

8. March 8, 2006Spectral RTL ATPG8 RTL Testing Approach (Circuit Characterization) RTL test generation: –Test vectors are generated for RTL faults (PI, PO and inputs - outputs of flip-flops.) Spectral analysis: –Test sequences for each input are analyzed using Hadamard matrix. –Essential components are currently determined by comparing their magnitudes H i with the mean of the total spectrum M. –Condition to pick-out essential components: –The process starts with the highest magnitude component and is repeated till the criteria is not satisfied.

9. March 8, 2006Spectral RTL ATPG9 Circuit b01: Coefficient Analysis (Vectors for RTL faults obtained from delay optimized circuit) Magnitudes of 32 Hadamard Coeffs. for 3 inputs of b01 Examples of essential components Examples of noise components

10. March 8, 2006Spectral RTL ATPG10 RTL Testing Approach (Test vector generation) Spectral Test Vector Generation: –Perturbation of spectral coefficients Retain essential spectral components Add random noise to replace the original identified noise. –Components considered non-essential are changed randomly both in magnitude and sign in a confined confidence level. –Generation of test vectors.

11. March 8, 2006Spectral RTL ATPG11 RTL Testing Approach (Test vector generation) Test Vector Compaction: –Characteristics of generated vectors depend on inserted noise. –Characteristics determine the fault coverage, the detectability of hard to detect faults, etc. –10 test sets are generated using the spectral method and compacted to achieve the best fault coverage. –Compaction currently performed by simple fault simulation of generated test sets on the target gate- level implementation. OK…I got that….. What about the RESULTS !!!

12. March 8, 2006Spectral RTL ATPG12 Experimental Results Spectral ATPG technique was applied to three ITC’99 high level RTL benchmark circuits, b01, b09 and b11 Characteristics of benchmark circuits: The benchmark circuits synthesized in two ways: –optimizing area –optimizing delay. Vectors for RTL faults obtained from ATPG (FlexTest). Spectral RTL-ATPG technique applied to the circuits. CircuitPIsPOsFFsFunction b01225FSM that compares serial flows b091128Serial to serial converter b117621Scramble string with variable cipher

13. March 8, 2006Spectral RTL ATPG13 RTL Spectral Characterization: b01 Number of RTL faults Number of Vectors RTL fault cov. (%) CPU* seconds Number of spectral components for three PIs Gate level fault cov. (%) of RTL vectors Area623891.941.0 (18, 8, 1) out of max. 64 92.98 Delay623191.941.0 (10, 1, 1) out of max. 32 83.10 * Sun Ultra 5, 256MB RAM

14. March 8, 2006Spectral RTL ATPG14 Gate-Level Test Generation: b01 Type of gate level synthesis Number of gate- level faults RTL ATPG Spectral Test Sets Gate-level ATPG Gate level cov. (%) Number of vectors CPU* seconds Gate level cov. (%) Number of vectors CPU* seconds Area optimized 22897.8112820.097.81751.0 Delay optimized 29097.4112820.098.28911.0 * Sun Ultra 5, 256MB RAM

15. March 8, 2006Spectral RTL ATPG15 Gate-Level Cov. of Spectral Test Sets on Area-Optimized b01 Circuit

16. March 8, 2006Spectral RTL ATPG16 Gate-Level Cov. of Spectral Test Sets on Delay-Optimized b01 Circuit

17. March 8, 2006Spectral RTL ATPG17 RTL Spectral Characterization: b09 Number of RTL faults Number of Vectors RTL fault cov. (%) CPU* seconds Number of spectral components for two PIs Gate level fault cov. (%) of RTL vectors Area24820268.55485 (1, 68) out of max. 256 73.98 Delay24831070.16413 (1,147) out of max. 512 68.75 * Sun Ultra 5, 256MB RAM

18. March 8, 2006Spectral RTL ATPG18 Gate-Level Test Generation: b09 Type of gate level synthesis Number of gate- level faults RTL ATPG Spectral Test Sets Gate-level ATPG Gate level cov. (%) Number of vectors CPU* seconds Gate level cov. (%) Number of vectors CPU* seconds Area optimized 88283.2662082584.52349296 Delay optimized 104882.7862081283.06335215 * Sun Ultra 5, 256MB RAM

19. March 8, 2006Spectral RTL ATPG19 Gate-Level Cov. of Spectral Test Sets on Area-Optimized b09 Circuit

20. March 8, 2006Spectral RTL ATPG20 Gate-Level Cov. of Spectral Test Sets on Delay-Optimized b09 Circuit

21. March 8, 2006Spectral RTL ATPG21 RTL Spectral Characterization: b11 Number of RTL faults Number of Vectors RTL fault cov. (%) CPU* seconds Number of spectral components for 9 PIs Gate level fault cov. (%) of RTL vectors Area24022468.53541 (66,62,54,55,6 3,51,60,1) out of max. 256 71.66 Delay24017472.35776 (66,70,59,61, 58,79,45,56) out of max. 256 76.78 * Sun Ultra 5, 256MB RAM

22. March 8, 2006Spectral RTL ATPG22 Gate-Level Test Generation: b11 Type of gate level synthesis Number of gate- level faults RTL ATPG Spectral Test Sets Gate-level ATPG Gate level cov. (%) Number of vectors CPU* seconds Gate level cov. (%) Number of vectors CPU* seconds Area optimized 238086.6251282681.854681866 Delay optimized 307084.92512106182.313653076 * Sun Ultra 5, 256MB RAM

23. March 8, 2006Spectral RTL ATPG23 Gate-Level Cov. of Spectral Test Sets on Area-Optimized b11 Circuit

24. March 8, 2006Spectral RTL ATPG24 Gate-Level Cov. of Spectral Test Sets on Delay-Optimized b11 Circuit Hmmm… interesting !

25. March 8, 2006Spectral RTL ATPG25 Conclusion Spectral RTL ATPG technique was applied to ITC’99 benchmark circuits b01, b09 and b11 and found to give favorable results in two out of the three circuits. Results indicate promise in further development of Spectral RTL ATPG technique. Test generation using Spectral RTL ATPG brings with it all the benefits of high level testing Techniques that will enhance Spectral ATPG are: –Efficient RTL ATPG –Accurate determination of noise components –Better ways of random noise insertion with more control over noise inserted –Better compaction algorithms

26. March 8, 2006Spectral RTL ATPG26 Future Work Model the test generation system in the frequency domain using transfer functions. Finding the relationship –Characterize input random vectors and output RTL vectors in the frequency domain –Obtain the transfer function for the Test generation system to target gate level faults Challenges in frequency domain –Linearity –Time-invariance Possible tools for frequency analysis: –Walsh functions –FFT ATPG Circuit under test Test generation system Random vecs. Test vectors Analytical model

27. March 8, 2006Spectral RTL ATPG27 Research Goals Extraction of spectral components from functional vectors and their application for test generation. Theoretical analysis of spectral components and the noise level. Consideration of both temporal and spatial spectra using two-dimensional signal analysis. Application to combinational and sequential circuits. Use of improved test generation for RTL faults. Effective application of vector compaction methods.

28. March 8, 2006Spectral RTL ATPG28 Thank You ! Any Questions ?