Effective TARO test pattern generation

1. Effective TARO test pattern generation By Intaik Park RATS (Reliability and Testability Seminar) Intaik Park, RATS, Summer 2004

2. Outline • Introduction • Basic Concepts • Algorithm • Experimental Result Intaik Park, RATS, Summer 2004

3. Introduction a b 1 • Normal transition fault patterns •  one path of each fault • TARO patterns •  all paths of each fault 2 c 3 d 4 5 e 6 f Fault site Output (PO+FF) Intaik Park, RATS, Summer 2004

4. TARO • TARO (Transition fault to All Reachable Outputs) test pattern • More thorough than a transition fault pattern • Can be generated without path analysis • Long test pattern generation time • Large test pattern size  longer test time  larger tester memory requirement Intaik Park, RATS, Summer 2004

5. Agenda • Need better way of generating TARO patterns • Need smaller pattern size Intaik Park, RATS, Summer 2004

6. Outline • Introduction • Basic Concepts • Algorithm • Experimental Result Intaik Park, RATS, Summer 2004

7. Required information • Need to propagate and detect faults through all reachable outputs of each fault  requires information about reachable outputs of each fault Intaik Park, RATS, Summer 2004

8. Definition • Reachable outputs : outputs through which a fault can be propagated and be detected • Detectable faults : faults that an output can observe and detect Intaik Park, RATS, Summer 2004

9. Reachable outputs a b 1 • Fault a output 1, 2 • Fault b output 2 • Fault c output 2, 3 • Fault d  output 4 • Fault e output 2, 3, 4, 5 • … 2 c 3 d 4 5 e 6 f Fault site Output (PO+FF) Intaik Park, RATS, Summer 2004

10. Detectable faults a b 1 • Output 1  Fault a • Output 2  Fault a, b, c, e • Output 3  Fault c, e • Output 4  Fault d, e • … 2 c 3 d 4 5 e 6 f Fault site Output (PO+FF) Intaik Park, RATS, Summer 2004

11. Detectable faults (contd.) • For TARO pattern generation, need reachable output list for each fault  find detectable fault list for each output • Logical corn analysis on cut (hard, inaccurate) • ATPG with output masks (easy, accurate) Intaik Park, RATS, Summer 2004

12. ATPG with output masks a b 1 • Output 2 unmasked • Masks on all other • outputs • Pattern will detect all • faults in detectable fault • list of output 2 2 c 3 d 4 5 e 6 f Fault site Output (PO+FF) Intaik Park, RATS, Summer 2004

13. Outline • Introduction • Basic Concepts • Algorithm • Experimental Result Intaik Park, RATS, Summer 2004

14. Simple algorithm • Run ‘ATPG with output masks’ on each output + Very fast ( no additional information necessary) – Large pattern size ( many don’t-care terms, unused outputs)  need more efficient algorithm Intaik Park, RATS, Summer 2004

15. Definition • Fault-output pair : a pair of fault site and one of its reachable output (a transition path) Intaik Park, RATS, Summer 2004

16. Efficient algorithm • Use output masks to control to which output the fault will propagate • Assign fault-output pairs that have outputs not masked • Let ATPG try best on each round of pattern generation Intaik Park, RATS, Summer 2004

17. Efficient Algorithm (Contd.) • After a transition fault ATPG • Not detected fault-output pair: • Fault a 1 output • c  2 • e  2, 3, 4 • e  4 • f  5 a b 1 2 c 3 d 4 5 e 6 f Used path Fault site Output (PO+FF) Unused path Intaik Park, RATS, Summer 2004

18. Efficient Algorithm (Contd.) a b 1 • Mask on output 2, 5, 6 • Fault a output 1 • Fault c excluded • Fault e 3 or 4 (or both) • Fault f 4 2 c 3 d 4 5 e Used path 6 f Unused path Fault site Output (PO+FF) Assigned path Intaik Park, RATS, Summer 2004

19. Efficient Algorithm (Contd.) a b • Fault assigned •  a, e, f • Output masked •  2, 5, 6 1 2 c 3 d 4 5 e Used path 6 f Unused path Fault site Output (PO+FF) Assigned path Intaik Park, RATS, Summer 2004

20. Efficient algorithm (contd.) start reachable output info ATPG with masks Verification by fault simulation All path detected? No Assign faults / masks Initial ATPG without masks Yes end Intaik Park, RATS, Summer 2004

21. Assignment • Greedy algorithm 1. Pick a fault that has unused path 2. Add used outputs to mask list 3. Add unused outputs to unmask list • ‘Order of pick’ makes difference • which fault to pick first? Intaik Park, RATS, Summer 2004

22. Assignment heuristics • Pick faults with … • Most reachable outputs first • Most unused path first • Least used path first • Least unused path first • Random Intaik Park, RATS, Summer 2004

23. Outline • Introduction • Basic Concepts • Algorithm • Experimental Result Intaik Park, RATS, Summer 2004

24. Experimental Result • ELF35 cores • 4 combinational cores • 1 translator, 3 datapaths • 2 sequential cores with full scan • 2901’s Intaik Park, RATS, Summer 2004

25. Elf35 Cores Intaik Park, RATS, Summer 2004

26. Core characteristics * For seq. cores, output = PO + scan FF Intaik Park, RATS, Summer 2004

27. Number of TARO patterns (comb.) * Number of patterns Intaik Park, RATS, Summer 2004

28. Number of TARO patterns (seq.) * Number of patterns Intaik Park, RATS, Summer 2004

29. Issues • Long running time • Depends on number of outputs and fault observability • Large pattern size • Many don’t care terms  Static compaction Intaik Park, RATS, Summer 2004

30. Future work • Finish TARO generation on sequential cores • Apply static compaction • Is TARO too thorough? Any way of excluding unnecessary thoroughness? Intaik Park, RATS, Summer 2004

31. Reference • Chao-Wen Tseng; McCluskey, E.J.;Test Conference, 2001. Proceedings. International , 30 Oct.-1 Nov. 2001 Pages:358 - 366 Intaik Park, RATS, Summer 2004

32. Previous work pattern length Intaik Park, RATS, Summer 2004

33. Core characteristics * For seq. cores, output = PO + scan FF Intaik Park, RATS, Summer 2004