1. Fall 2006, Nov. 30 ELEC 5270-001/6270-001 Lecture 12 1 ELEC 5270-001/6270-001(Fall 2006) Low-Power Design of Electronic Circuits Test Power Vishwani D. Agrawal James J. Danaher Professor Department of Electrical and Computer Engineering Auburn University, Auburn, AL 36849 http://www.eng.auburn.edu/~vagrawal vagrawal@eng.auburn.edu

2. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 122 Test Power Problem A circuit is designed for certain function. Its design must allow the power consumption necessary to execute that function. A circuit is designed for certain function. Its design must allow the power consumption necessary to execute that function. Power buses are laid out to carry the maximum current necessary for the function. Power buses are laid out to carry the maximum current necessary for the function. Heat dissipation of package conforms to the average power consumption during the intended function. Heat dissipation of package conforms to the average power consumption during the intended function.

3. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 123 Testing Differs from Function VLSI chip system System inputs System outputs Functional inputs Functional outputs Other chips

4. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 124 Basic Mode of Testing VLSI chip Test vectors: Pre-generated and stored in ATE DUT output for comparison with expected response stored in ATE Automatic Test Equipment (ATE): Control processor, vector memory, timing generators, power module, response comparator Power Clock Packaged or unpackaged device under test (DUT)

5. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 125 Functional Inputs vs. Test Vectors Functional inputs: Functional inputs: Functionally meaningful signals Functionally meaningful signals Generated by circuitry Generated by circuitry Restricted set of inputs Restricted set of inputs May have been optimized to reduce logic activity and power May have been optimized to reduce logic activity and power Test vectors: Test vectors: Functionally irrelevant signals Generated by software to test faults Can be random or pseudorandom May be optimized to reduce test time; can have high logic activity May use testability logic for test application

6. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 126 An Example VLSI chip Binary to decimal converter 3-bit random vectors 8-bit 1-hot vectors VLSI chip system VLSI chip in system operation VLSI chip under test High activity 8-bit test vectors from ATE

7. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 127 Reducing Comb. Test Power 1 1 0 0 0 1 0 1 0 0 1 0 1 0 1 1 0 1 1 1 V1V2V3 V4V5 34 1 3 2 2 3 2 1 1 V1 V2 V3 V4 V5 10 input transitions Traveling salesperson problem (TSP): Find the shortest distance closed path (or cycle) to visit all nodes exactly once. V1 V3 V5 V4 V2 1 0 0 0 1 1 1 0 0 0 1 1 1 0 0 1 1 1 1 0 5 input transitions

8. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 128 Traveling Salesperson Problem A. V. Aho, J. E. Hopcroft anf J. D. Ullman, Data Structures and Algorithms, Reading, Massachusetts: Addison-Wesley, 1983. A. V. Aho, J. E. Hopcroft anf J. D. Ullman, Data Structures and Algorithms, Reading, Massachusetts: Addison-Wesley, 1983. E. Horowitz and S. Sahni, Fundamentals of Computer Algorithms, Computer Science Press, 1984. E. Horowitz and S. Sahni, Fundamentals of Computer Algorithms, Computer Science Press, 1984.

9. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 129 Scan Testing Combinational logic Scan flip- flops Primary inputs Primary outputs Scan-in SI Scan-out SO Scan enable SE DFF mux SE SI D D D’ SO 1010

10. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 1210 Example: State Machine S5 S1 S4 S2 S3 Reduced power state encoding S1 = 000 S2 = 011 S3 = 001 S4 = 010 S5 = 100 State transition Comb. Input changes 000 → 001 1 000 → 100 1 011 → 010 1 001 → 011 1 010 → 000 1 100 → 010 2 Functional transitions

11. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 1211 Scan Testing of State Machine Combinational logic FF=0 FF=1 Primary inputs Primary outputs Scan-in 010 Scan-out 100 State transition Comb. Input changes 100 → 010 2 010 → 101 3 101 → 010 3 Test transitions

12. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 1212 Low Power Scan Flip-Flop DFF mux SE SI D DFF mux SE SI D SO D’ SO Scan FF cellLow power scan FF cell 1010

13. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 1213 Built-In Self-Test (BIST) Linear feedback shift register (LFSR) Multiple input signature register (MISR) Circuit under test (CUT) Pseudo-random patterns Circuit responses BIST Controller Clock C. E. Stroud, A Designer’s Guide to Built-In Self-Test, Boston: Kluwer Academic Publishers, 2002.

14. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 1214 Test Scheduling Example R1R2 M1 M2 R3R4 A datapath

15. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 1215 BIST Configuration 1: Test Time LFSR1LFSR2 M1 M2 MISR1MISR2 Test time Test power T1: test for M1 T2: test for M2

16. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 1216 BIST Configuration 2: Test Power R1LFSR2 M1 M2 MISR1MISR2 Test time Test power T1: test for M1 T2: test for M2

17. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 1217 Testing of MCM and SOC Test resources: Typically registers and multiplexers that can be reconfigured as test pattern generators (e.g., LFSR) or as output response analyzers (e.g., MISR). Test resources: Typically registers and multiplexers that can be reconfigured as test pattern generators (e.g., LFSR) or as output response analyzers (e.g., MISR). Test resources (R1,...) and tests (T1,...) are identified for the system to be tested. Test resources (R1,...) and tests (T1,...) are identified for the system to be tested. Each test is characterized for test time, power dissipation and resources it requires. Each test is characterized for test time, power dissipation and resources it requires.

18. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 1218 Resource Allocation Graph T1T2T3T4T5T6 R2R1R3R4R5R6R7R8R9

19. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 1219 Test Compatibility Graph (TCG) T1 (2, 100) T2 (1,10) T3 (1, 10) T4 (1, 5) T5 (2, 10) T6 (1, 100) Tests that form a clique can be performed concurrently. Power Test time Pmax = 4

20. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 1220 Test Scheduling Algorithm Identify all possible cliques in TCG: Identify all possible cliques in TCG: C1 = {T1, T3, T5} C1 = {T1, T3, T5} C2 = {T1, T3, T4} C2 = {T1, T3, T4} C3 = {T1, T6} C3 = {T1, T6} C4 = {T2, T5} C4 = {T2, T5} C5 = {T2, T6} C5 = {T2, T6} Break up clique sets into power compatible sets (PCS), that satisfy the power constraint. Break up clique sets into power compatible sets (PCS), that satisfy the power constraint.

21. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 1221 Test Scheduling Algorithm... PCS (Pmax = 4), tests within a set are ordered for decreasing test length: PCS (Pmax = 4), tests within a set are ordered for decreasing test length: C1 = {T1, T3, T5} → (T1, T3), (T1, T5), (T3, T5) C1 = {T1, T3, T5} → (T1, T3), (T1, T5), (T3, T5) C2 = {T1, T3, T4} → (T1, T3, T4) C2 = {T1, T3, T4} → (T1, T3, T4) C3 = {T1, T6} → (T1, T6) C3 = {T1, T6} → (T1, T6) C4 = {T2, T5} → (T2, T5) C4 = {T2, T5} → (T2, T5) C5 = {T2, T6} → (T2, T6) C5 = {T2, T6} → (T2, T6) Expand PCS into subsets of decreasing test lengths. Each subset is an independent test session, consisting of tests that can be concurrently applied. Expand PCS into subsets of decreasing test lengths. Each subset is an independent test session, consisting of tests that can be concurrently applied. Select test sessions to cover all tests such that the added time of selected sessions is minimum. Select test sessions to cover all tests such that the added time of selected sessions is minimum.

22. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 1222 TS Algorithm: Cover Table Test sessions T1T2T3T4T5T6Length (T1, T3, T4) XXX100 (T1, T5) XX100 (T1, T6) XX100 (T2, T6) XX100 (T3, T5) XX10 (T2, T5) XX10 (T3, T4) XX10 (T5)X10 (T4)X5 Selected sessions are (T3,T4), (T2, T5) and (T1, T6). Test time = 120.

23. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 1223 A System Example: ASIC Z* RAM 2 Time=61 Power=241 RAM 3 Time=38 Power=213 ROM 1 Time=102 Power=279 ROM 2 Time=102 Power=279 RAM 1 Time=69 Power=282 RAM 4 Time=23 Power=96 Reg. file Time = 10 Power=95 Random logic 1, time=134, power=295 Random logic 2, time=160, power=352 *Y. Zorian, “A Distributed Control Scheme for Complex VLSI Devices,” Proc. VLSI Test Symp., April 1993, pp. 4-9.

24. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 1224 Test Scheduling for ASIC Z 1200 900 600 300 Power Power limit = 900 0 100 200 300 400 Test time 331 RAM 1 RAM 3 Random logic 2 Random logic 1 ROM 2 ROM 1 RAM 2 Reg. file RAM 4 R. M. Chou, K. K. Saluja and V. D. Agrawal, “Scheduling Tests for VLSI Systems under Power Constraints,” IEEE Trans. VLSI Systems, vol. 5, no. 2, pp. 175-185, June 1997.

25. Fall 2006, Nov. 30ELEC 5270-001/6270-001 Lecture 1225 References N. Nicolici and B. M. Al-Hashimi, Power- Constrained Testing of VLSI Circuits, Boston: Kluwer Academic Publishers, 2003. N. Nicolici and B. M. Al-Hashimi, Power- Constrained Testing of VLSI Circuits, Boston: Kluwer Academic Publishers, 2003. E. Larsson, Introduction to Advanced System-on-Chip Test Design and Optimization, Springer 2005. E. Larsson, Introduction to Advanced System-on-Chip Test Design and Optimization, Springer 2005.