1. May 11, 2006High-Level Spectral ATPG1 High-Level Test Generation for Gate-level Fault Coverage Nitin Yogi and Vishwani D. Agrawal Auburn University Department of ECE Auburn, AL 36849

2. May 11, 2006High-Level Spectral ATPG2 Outline Need for High Level Testing Problem and Approach Spectral analysis and generation of test sequences RTL testing approach Experimental Results Conclusion

3. May 11, 2006High-Level Spectral 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. May 11, 2006High-Level Spectral ATPG4 Problem and Approach The problem is … –Develop synthesis-independent ATPG methods using RTL circuit description. And our approach is: –Implementation-independent characterization: RTL test generation Characterization of RTL vectors for spectral components and the noise level for each PI of the circuit. –Test generation for gate-level implementation: Generation of spectral vectors Fault simulation and vector compaction That’s fine ! But does it work ?

5. May 11, 2006High-Level Spectral ATPG5 RTL Faults Combinational Logic FF Inputs Outputs RTL stuck-at fault sites

6. May 11, 2006High-Level Spectral ATPG6 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 basis functions that can represent any arbitrary bit-stream. Walsh functions are the rows of the Hadamard matrix. Example of Hadamard matrix of order 8: OK…so its just another way of representing information

7. May 11, 2006High-Level Spectral ATPG7 Characterizing a Bit-Stream A bit-stream is correlated with each row of Hadamard matrix. Highly correlated basis Walsh functions are retained as essential components and others are regarded as noise. Bit stream to analyze Correlating with Walsh functions by multiplying with Hadamard matrix. Essential component (others noise) Hadamard Matrix Bit stream Spectral coeffs.

8. May 11, 2006High-Level Spectral ATPG8 Test Vector Generation Spectrum for new bit-streams consists of the essential components and added random noise. Essential component plus noise spectra 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 their noise spectrum. Perturbation 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

9. May 11, 2006High-Level Spectral ATPG9 RTL Testing Approach (Circuit Characterization) RTL test generation: –Test vectors are generated for RTL faults (PIs, POs 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 power H i 2 with the average power per component M 2. –Condition to pick-out essential components: where K is a constant –The process starts with the highest magnitude component and is repeated till the criteria is not satisfied.

10. May 11, 2006High-Level Spectral ATPG10 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

11. May 11, 2006High-Level Spectral ATPG11 Selecting Minimal Vector Sequences Using ILP A set of perturbation vector sequences {V 1, V 2,.., V M } 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 {V 1, …,V M } to obtain compressed seq. {V 1,…,V C } where {V 1, …,V C } {V 1, …, V M } Count {V 1, …,V C } ≤ Count {V 1, …,V M } Fault Coverage {V 1, …,V C } = Fault Coverage {V 1, …,V M } Compaction problem is formulated as an Integer Linear Program (ILP) [1]. OK…I got that….. What about the RESULTS !!! [1] P. Drineas and Y. Makris, “Independent Test Sequence Compaction through Integer Programming," Proc. ICCD’03, pp. 380-386.

12. May 11, 2006High-Level Spectral ATPG12 Experimental Results RTL Spectral ATPG technique applied to the following benchmarks: –three ITC’99 high level RTL circuits –four 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. CircuitbenchmarkPIsPOsFFs b01ITC’99225 b09ITC’991128 b11ITC’997631 b14ITC’993454239 s1488ISCAS’898196 s5378ISCAS’893649179 s9234ISCAS’893739211 s35932ISCAS’89363201728 PARWANprocessor112353

13. May 11, 2006High-Level Spectral ATPG13 Results for b11-A No. of RTL faults Number of Vectors RTL test cov. (%) CPU* seconds No. of spec. components Gate level test cov. (%) of RTL vecs. 24022476.1653025674.09 * Sun Ultra 5, 256MB RAM No. 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 238088.8476873784.624681866 RTL characterization: RTL-ATPG results:

14. May 11, 2006High-Level Spectral ATPG14 b11-A Circuit

15. May 11, 2006High-Level Spectral ATPG15 PARWAN processor

16. May 11, 2006High-Level Spectral ATPG16 Results Circuit name No. of gate- level faults RTL-ATPG spectral testsGate-level ATPGRandom inputs Cov. (%) No. of vectors CPU (secs) Cov. (%) No. of vectors CPU (secs) No. of vectors Cov (%) b01-A22899.571281999.7775164097.78 b01-D29098.771281999.7791164095.80 b09-A88284.6864073084.56436384384011.71 b09-D104884.2176881578.8255557576806.09 b11-A238088.8476873784.624681866384045.29 b11-D307089.25102498786.163653076384041.42 b142589485.096656543668.7850065741280074.61 s1488418495.6551210398.42470131160067.47 s53781558476.492432208876.798354439384067.10 s5378*1594473.59139971873.3133222567288062.77 s92342897617.366472120.1469671824116015.44 s9234*2940049.47832273448.74123654119217633.06 s3593210320495.70256180195.99744319232050.70 PARWAN538089.111344100687.117183626640076.63 * Reset input added.

17. May 11, 2006High-Level Spectral ATPG17 Conclusion Spectral RTL ATPG technique applied to three ITC’99 and four ISCAS’89 benchmarks, and a processor circuit. Results indicate promise in further development of the 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 and use of noise components –Better compaction algorithms Future work: Spectral characterization of functional vectors.

18. May 11, 2006High-Level Spectral ATPG18 Thank You ! Questions ?