Dec. 19, 2005ATS05: Agrawal and Doshi1 Concurrent Test Generation Auburn University, Department of Electrical and Computer Engineering Auburn, AL 36849, USA Vishwani D. Agrawal Alok S. Doshi

Dec. 19, 2005ATS05: Agrawal and Doshi2 Problem Statement To find the smallest test set to detect all single stuck-at faults in a combinational circuit. An existing solution: –Group faults into fault sets using fault independence –Generate concurrent tests for each group Contribution of this paper: Devise a simulation- based implementation for this solution.

Dec. 19, 2005ATS05: Agrawal and Doshi3 Outline Introduction Simulation-based Independence Fault Collapsing Simulation-based Concurrent Test Generation Results Conclusions

Dec. 19, 2005ATS05: Agrawal and Doshi4 Introduction v1v1 v2v2 v3v3... T(F1) T(F2) Problem of finding a minimal test: Static compaction cannot guarantee optimality. Dynamic compaction is complex. Solution: Target both faults F1 and F2 at the same time to find a single test. We define this as concurrent test generation. Test set for fault F1 Test set for fault F2

Dec. 19, 2005ATS05: Agrawal and Doshi5 Fault Classification F1 and F2 are equivalent. F1 dominates F2. F1 and F2 are independent. F1 and F2 are concurrently testable. T(F1) = T(F2) T(F1) T(F2) T(F1) T(F2) T(F1)

Dec. 19, 2005ATS05: Agrawal and Doshi6 Example Circuit a b c d e x y C17 - ISCAS85 Benchmark Circuit 1 R. K. K. R. Sandireddy and V. D. Agrawal, “Diagnostic and Detection Fault Collapsing for Multiple Output Circuits,” Proc. Design, Automation and Test in Europe (DATE) Conf., Mar. 2005, pp All faults are Stuck-at-1 type

Dec. 19, 2005ATS05: Agrawal and Doshi7 Independence Matrix and Graph C17 - ISCAS85 Benchmark Circuit F

Dec. 19, 2005ATS05: Agrawal and Doshi8 Independence Fault Collapsing 1,8 5,11,7 3,9,2 4,6,10 2 A. S. Doshi and V. D. Agrawal, “Independence Fault Collapsing,” Proc. 9 th VLSI Design and Test Symp., Aug. 2005, pp C17 - ISCAS85 Benchmark Circuit A “similarity” based algorithm [2] collapses the independence graph:

Dec. 19, 2005ATS05: Agrawal and Doshi9 Simulation-based Independence Fault Collapsing 2 A. S. Doshi and V. D. Agrawal, “Independence Fault Collapsing,” Proc. 9 th VLSI Design and Test Symp., Aug. 2005, pp The independence graph generation procedure [2] requires ATPG. Here we present a new method for graph generation using simulation: –Start with a fully-connected independence graph for an equivalence collapsed fault set. –Simulation of random vectors without fault dropping removes edges between faults detected by the same vector.

Dec. 19, 2005ATS05: Agrawal and Doshi10 Simulation-based Independence Fault Collapsing bit ALU 301

Dec. 19, 2005ATS05: Agrawal and Doshi11 Simulation-based Concurrent Test Generation For each group, generate all test vectors for the first fault in the group. –If the number of test vectors for a fault is large, use a subset (e.g., 250 maximum) of vectors. Simulate all faults in the group to select one vector that detects most faults in that group. –If more vectors than one detect the same number of faults within the group, then select the vector that detects most faults outside the group as well.

Dec. 19, 2005ATS05: Agrawal and Doshi bit ALU Result Group numberNumber of faults in groupConcurrent test vector All 56 faults detected by eleven previously generated vectors

Dec. 19, 2005ATS05: Agrawal and Doshi13 * Sun Ultra 5 *** Pentium Pro PC ** Hamzaoglu and Patel, IEEE-TCAD, 2000 Results Circuit No. of concurrent groups Concurrent ATPG Single-fault ATPG VectorsCPU s* AtalantaBest known VectorsCPU s*VectorsCPU s*** 1-b adder 2-b adder 4-b adder 8-b adder 16-b adder 32-b adder 4-b ALU c17 c432 c499 c880 c1355 c1908 c2670 c3540 c5315 c6288 c ** 52** 16** 84** 106** 44** 84** 37** 12** 73**

Dec. 19, 2005ATS05: Agrawal and Doshi14 Number of Vectors for Increasing Circuit Sizes (100% Stuck-at Coverage) Single-fault ATPG (no compaction) Concurrent ATPG Minimum achieved! (dynamic compaction)

Dec. 19, 2005ATS05: Agrawal and Doshi15 CPU Seconds for Increasing Circuit Sizes (100% Stuck-at Fault Coverage) Concurrent ATPG Minimum achieved! (dynamic compaction)

Dec. 19, 2005ATS05: Agrawal and Doshi16 Conclusion Concurrent test generation produces compact tests when combined with independence fault collapsing. ATPG and set covering problems have exponential time complexities. Hence, we cannot expect absolute optimality for large circuits. The concurrent ATPG procedure of this paper gives significantly smaller, and sometimes the optimum, test sets. There is scope for improving the simulation-based algorithms for independence fault collapsing and concurrent test generation.

Dec. 19, 2005ATS05: Agrawal and Doshi17 Thank You!