Thermal-Aware SoC Test Scheduling with Test Set Partitioning and Interleaving Zhiyuan He 1, Zebo Peng 1, Petru Eles 1 Paul Rosinger 2, Bashir M. Al-Hashimi 2 1 Linköping University, Sweden 2 University of Southampton, U.K.

2 Core-based System-on-Chip Integration of pre-designed and pre-verified cores in a single chip Advantages Reduced design complexity Lower cost Shorter time-to-market Challenges to testing Large quantities of test data, long test time High power consumption, high temperature Need efficient test approach

3 Increasing Power Density High power density  high temperature on chip! Source: Fred Pollack (Intel Corp.), Micro32, “New Microarchitecture Challenges in the Coming Generations of CMOS Process Technologies”

4 Thermal Issue in SoC Test Higher power dissipation during test than in normal operations [Pouya, ITC’00] High temperature during test Slow down transistors Large RC delay High leakage Shorter lifetime Permanent damage Require temperature- aware test techniques

5 Contribution An SoC test scheduling technique that Minimizes test application time Prevents over-heating during test Utilizing test set partitioning and interleaving

6 Outline Basic Test Architecture Test Set Partitioning and Interleaving Problem Formulation Constraint Logic Programming (CLP) Experimental Results and Conclusions

7 Basic Test Architecture Tester Test controller Tester memory On-chip or external Test bus (single) Bandwidth limit Dedicated TAM wires connecting cores to the test bus

8 Test Set Partitioning

9 Test Set Interleaving Test for Core 1 Test for Core 2

10 The Basic Strategy Generate an initial partitioning scheme (thermal-safe, min number of partitions) using temperature simulation (HotSpot) Generate alternative partitioning schemes w.r.t. the number of partitions Generate the optimal test schedule constrained by a bus bandwidth limit

11 Assumption A test set is partitioned into test sequences with equal lengths, except the first one To simplify the test controller To reduce design space

12 A Motivational Example

13 Test Time Minimization Problem Input Test architecture Test sets for all cores Test bus bandwidth limit B max Temperature upper limit TM i,max for each core C i Output The optimized test schedule Objective Minimize the total test time TTT Subject to –Total amount of bus bandwidth utilization B < B max –Temperature of each core TM i < TM i,max

14 Constraint Logic Programming Define relationships or constraints by using logic programming language Provide solvers to find optimal solutions Exhaustive search Branch and bound CHIP Developed by COSYTEC Uses Prolog Integrated solvers

15 Experimental Results # of Cores # of Partitioning Schemes Problem Size Total Test Times (# of clock cycles) CPU Times (s)

16 Conclusions An exact approach to minimize total test time for SoC test under a temperature upper limit and bus bandwidth limit Proposed test set partitioning and interleaving techniques Optimal solution obtained by using constraint logic programming

17 Thank you!