Modular SOC Testing With Reduced Wrapper Count Qiang Xu; Nicolici, N., “Modular SOC testing with reduced wrapper count”, IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, Dec. 2005, Page(s): Presented By: Yuyan Xue (April. 2007)

Reduced-Wrapper-Count Testing2 Motivation Modular test strategies (Wrapper, dedicated bus-based TAM) enable the reusability, scalability and interoperability in DFT. Modular test strategies add the overall cost of the test. Modular test strategies deteriorate the system performance if they stand on the critical path.

Reduced-Wrapper-Count Testing3 Objective Reduce the wrapper count, meanwhile maintaining the benefits of modular SOC testing. Compatible to IEEE P1500 standard, meanwhile investigate the suitability of reusing the functional interconnect for transferring test data

Reduced-Wrapper-Count Testing4 Idea from IEEE P1500 INTEST/EXTEST Producer/Consumer A core can be tested without wrapping its terminals as long as all its producers and consumers are P1500-wrapped.

Reduced-Wrapper-Count Testing5 New Wrapper Design for Embedded Cores No wrapper at all (INTEST/EXTEST modes only) Light wrapper without WBR (RAM/ROM for BIST) Parallel Bypass Register (WBY) Revised P1500 Wrapper for P/C cores.

Reduced-Wrapper-Count Testing6 New Test Conflicts Caused Traditional TAM lines conflict in IEEE P1500 New test conflicts Producer-CUT Core6->2,5,9 CUT-Consumer Core2->6,7,8,9 Shared-Producer Core7,8->2 Shared-Consumer Core3,6->5 Shared-Bus Core1,5->8

Reduced-Wrapper-Count Testing7 TAM Division Into Three Groups Flexible- width test for G CUT Daisy chain for G prod and G cons

Reduced-Wrapper-Count Testing8 Wrapper/TAM Co-optimization Given: PIs, POs, bidirectional I/Os, test patterns, scan chains and scan chain length, total TAM width, wrapper design constrains Output: the width of each TAM group, wrapper design for each core, the test schedule Satisfy: wrapper design constrains, maximized light-wrapper number, TAM width constrains, minimized overall SOC TAT

Reduced-Wrapper-Count Testing9 Three Types of Wrapper Design Constraints Critical Path -> Light wrapper Cores with P1500 wrapper provided Two-pattern tested ( delay and stuck- open fault)

Reduced-Wrapper-Count Testing10 TAM Division and Test Scheduling Algorithm Determine light-wrapped cores <-functional interconnection & wrapper design constraints Create Test Incompatible Graph (TIG) Enumeratively find the optimal TAM division and the minimum system TAT. Worst case complexity

Reduced-Wrapper-Count Testing11 Decide Wrapper Type Given: the set of cores, the functional interconnect relationship, wrapper design constrains Output: wrapper type for each core Methodology: Wrapper status initialization ( wrapper constraints) Light-wrapped as default and compute test dependency. Choose cores with less test dependency

Reduced-Wrapper-Count Testing12 Construct TIG Given: the set of cores, test conflicts Output: node for core and edge for conflicts between two cores Conflicts only exist between: Two light-wrapped cores A Light-wrapped core and its producers/consumers

Reduced-Wrapper-Count Testing13 Rectangle representation for P1500-wrapped core Rectangle representation for light-wrapped core Dynamic Rectangle Representation

Reduced-Wrapper-Count Testing14 Adaptive Dynamic Rectangle Packing Given: the set of cores, TIG, TAM division Output: schedule for each core, overall TAT of the SOC Methodology: Find out pareto-optimal TAM width Schedule cores using the preferred width, as long as TAM width is sufficient Pack the idle time with remaining test Repeat scheduling process for remaining test if one test is completed

Reduced-Wrapper-Count Testing15 Experimental Result

Reduced-Wrapper-Count Testing16 Experimental Result (Continued)

Reduced-Wrapper-Count Testing17 Contributions Light-wrapped core is introduced to reduce the number of wrapper cells in the SOC without impacting its testability. Up to half of the cores can be unwrapped without affecting the test quality. New modular SOC test architecture is proposed, which employs three separate TAM groups and facilitates concurrent testing of both P1500-wrapped cores and light-wrapped cores. New algorithms for wrapper/TAM co- optimization and test scheduling is introduced.