1 Pattern-Directed Circuit Virtual Partitioning for Test Power Reduction Qiang Xu The Chinese University of Hong Kong Dianwei Hu and Dong Xiang Tsinghua University Beijing, China

2 Outline Background Pattern-Directed Virtual Partitioning Routing-Aware Virtual Partitioning Experimental Results Conclusion

3 Test Power Toggle rate in test mode may be significantly higher than that in functional mode  Excessive accumulated power -> permanent damage  Excessive instantaneous power -> test yield loss Excessive test power is a major concern!

4 Prior Work on Test Power Reduction Scan chain manipulation:  Scan chain partitioning (e.g., Whetsel ITC’02)  Scan chain reordering (e.g., Bonhomme ITC’02) Test vector manipulation:  Power-aware ATPG (e.g., Wang TCAD ’ 98)  Low-power X-filling (e.g., Butler ITC’04, Wen ITC ’ 05)  Test vector reordering (e.g., Dabholkar TCAD’98 ) Test scheduling Circuit modification

5 Circuit Partitioning for Test Power Reduction Tester Data SE TCK Glue Logic Circuit under Test wrapper Scan chain P1 wrapper Scan chain P2

6 Observations and Motivation Test patterns’ power consumptions vary significantly Only a few “care-bits” necessary for a test pattern to detect all the faults covered by it Applying high-power patterns at a partitioned subcircuit containing all their care-bits reduces test power without fault coverage loss

7 Virtual Circuit Partitioning High-power Patterns Glue Logic Circuit under Test Scan chain P1 Scan chain P2 Low-power Patterns

8 Problem Definition How to partition the circuit such that the “care-bits” of as many as possible high-power patterns belong to a single partition?

9 Design Flow Start (with given specified patterns ) Rank test patterns based on capture power Fault simulation Identify care-bits for the high-power patterns Iteratively partition the circuit Meet constraints End Yes No

10 Care-Bits Identification Let low-power patterns detect as many faults as possible Response care-bits: fault simulation Stimulus care-bits: limited implication Cost function, depends on:  Care-bits selected by previous patterns  Comparison between different response care- bits

11 Care-Bits Identification sa (0 ) 0(1 ) Response Carebits

12 Care-Bits Identification sa (0) 0(1) Stimuli Carebits

13 Care-Bits Identification sa (0) 0(1) Stimuli Carebits

14 Iterative Partitioning P1 F1 P2 F2 P3 F3F4 High power Low power Patterns Faults Fault simulation

15 Iterative Partitioning P2 F2 P3 F3F4 I1I1, I2 R1R2 I1 R1 Patterns Faults High power Low power P1 F1

16 Iterative Partitioning R4 I3, I4 I1, R1 I3, I4, R4 Patterns Faults P2 F2 P3 F3F4 P1 F1 High power Low power

17 Iterative Partitioning R1 I2 Patterns Faults P2 F2 P3 F3F4 P1 F1 High power Low power I1, R1 I3, I4, R4 I1, R1, I2

18 Iterative Partitioning R1 R3 I3, I4 I2 I1, I2 Patterns Faults P2 F2 P3 F3F4 P1 F1 High power Low power I3, I4, R4 I1, R1, I2

19 Routing-Aware Partitioning Partitioning significantly affects scan chain routing cost Solution: constraint-driven partitioning  Model the spreadness of the scan FFs  Divide the circuit layout into sub-regions  Routing either horizontally or vertically in a snake-like way

20 RA-Partitioning Design Flow Start (with given specified patterns) Rank test patterns based on capture power Fault simulation Identify care-bits for the high-power patterns Iteratively partition the circuit Meet constraints End Yes No Iteratively partition the circuit with routing consideration

21 Routing-Aware Partitioning – Cont. (150,180) (130,100) (80,100) (40,40) ( 0,220 ) ( 250,220 ) (0,0) (250,0) H V d b c a = =130 CUT

22 Routing-Aware Partitioning – Cont. (150,180) (130,100) (80,100) (40,40) (0,220) (250,220) (0,0) (250,0) H V d b c a 70 += CUT 10

23 Iterative Partitioning Routing-Aware Partitioning Experimental Result – s38417 (stuck-at)

24 Experimental Result – s38584 (broadside) Iterative Partitioning Routing-Aware Partitioning

25 Power comparison for stuck-at Average power with VP: 49.13% Average power with RA-VP: 57.67%

26 Wire length comparison for stuck-at Average wire length with VP: % Average wire length with RA-VP: %

27 Power comparison for broad-side Average power with VP: 63.59% Average power with RA-VP: 68.28%

28 Wire length comparison for broad-side Average wire length with VP: % Average wire length with RA-VP: %

29 Conclusion Excessive test power is a major concern today We propose routing-aware circuit virtual partitioning technique for test power reduction  without adding test wrappers  without fault coverage loss  with small scan chain routing cost