On Reliable Modular Testing with Vulnerable Test Access Mechanisms
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On Reliable Modular Testing with Vulnerable Test Access Mechanisms
On Reliable Modular Testing with Vulnerable Test Access Mechanisms
Lin Huang, Feng Yuan and Qiang Xu
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PurposePurpose
Is on-chip data transmission reliable?
What is the solution? Correction Retransmission Hybrid schemes
They are helpful in normal functional modenormal functional mode
However, how about modular testing modular testing?
Cross talk
IR drop
and even alpha particle hits …
Yield loss
Yield loss
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AgendaAgenda
Introduction to Modular Testing
Test Data Transmission “Error-Free” Assumption
Impact of Fault-Tolerant Schemes
The Proposed Solution “Jitter-Aware” Test Wrapper Design “Jitter-Transparent” ATE Interface Design
Experimental Results
Conclusion
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Introduction to Modular TestingIntroduction to Modular Testing
“Divide and conquer” manner test wrapper test access mechanisms (TAMs) ATE Interface basic
TAM designs classification dedicated bus-based access scheme functional access schemefunctional access scheme
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Reuse On-Chip Network as TAMReuse On-Chip Network as TAM
ATE
Legend
Core
ATE Interface
NI
MUX
Router
System Input
System Output
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“Error-Free” Assumption is Questionable“Error-Free” Assumption is Questionable
Existing work assumes test data transmission to be error-free
It is questionable when at-speed functional interconnects are reused as TAMs
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Fault Tolerance SchemesFault Tolerance Schemes
Retransmission and hybrid schemes are mainstream techniques to achieve fault-tolerant communication
Retransmission brings problems Test traffic jitter Test bandwidth mismatch
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The Impact of Retransmission SchemeThe Impact of Retransmission Scheme
CUT & Wrapper
CHIP UNDER TEST
ATE
In Path ATE IF
In Path ATE NI
In Path Router 1
In Path Router j
In Path Router j+1
In Path Router m
CUT Router
CUT NI
Out Path Router 1
Out Path Router n
Out Path ATE NI
Out Path ATE IF
Flit Error
NACKSequential Flits are Blocked here
Retransmission
TestTrafficJitter
TestBandwidthMismatch
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The Significance of These ProblemsThe Significance of These Problems
Given the number of flits in the entire test data volume , the flit error rate , the potential yield loss can be expressed as
When and flit size is 32 bits, the test yield loss for the chip containing 21.5M gates [1] is
1 1N
YieldLoss
N
910
[1] C. Barnhart et al, Extending OPMISR Beyond 10x Scan Test Efficiency.IEEE Design & Test of Computers, 19(5):65-73, Sep.-Oct. 2002
11.47% !
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Buffer-Only SolutionBuffer-Only Solution
Given the flit injection rate is 0.1 flits per cycleand the extra delay caused by one retransmission is 40 cycles
The 1st
retransmissionThe 2nd
retransmission
5 reserved flits 1 reserved flits
Shortage ofreserved flits
5 40 0.1 1
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“Jitter-Aware” Test Wrapper Design“Jitter-Aware” Test Wrapper Design
Two extra states: HALTIN
HALTOUT
CAPTRUE SHIFT
HALTOUT
HALTIN
OutputBlocked
InputBlocked
IEEE 1500Finite State Machine
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Wrapper ArchitectureWrapper Architecture
NETWORK INTERFACE
TEST WRAPPER
Gated_Clk Scan_En
Control Logic
Bd
. Mat
chin
g U
nit
Bd
. Mat
chin
g U
nit
CUT
Input Channel Output Channel
Dat
a
Dat
a
Co
ntr
ol
Co
ntr
ol
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Control Logic of Test WrapperControl Logic of Test Wrapper
Block_Ctrl
IPath_Blocked
OPath_Blocked
IBMU_Ctrl
SCmdAccept_In
MCmd_Out
SCmdAccept_Out
MCmd_In
Scan_En
Input Control
Output Control
Control Logic
WrapperKernel Control
ClockDivision
OCP_Clk
Gated_Clk
Scan_Clk
OBMU_Ctrl
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“Jitter-Transparent” ATE Interface“Jitter-Transparent” ATE Interface
If the ATE operate in a stream mode …
Minimum buffer size: that is able to tolerate the extra delay caused by one retransmission
Given the flit error rate and the number of flits , the test yield loss can be computed as follows:
11 1 1
N N
BYieldLoss N
N
1 1N
YieldLoss Without Buffer:
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On-Chip Network
ATE Interface
Test Vector(w. don’t care bits)
Test Vector(w.o. don’t care bits)
Test Response(w. jitter)
Test Response(w. don’t care bits)
ATE
“don’t care” bitsmeaningful information in the input data data
meaningful information in the output data data
Expected Response
“Jitter-Transparent” ATE Interface“Jitter-Transparent” ATE Interface
We propose to divide the entire input test data flow into segments and insert a small section of “don’t-care” bits
r
Data transmission direction
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Test Yield ImprovementTest Yield Improvement
r
1
& 1 1 1rN N
r rB S
NYieldLoss
r
NGiven the flit error rate , the number of flits , and the number of segments , the test yield loss can be computed as follows:
1 1N
YieldLoss Without Buffer:
With Minimum Buffer Size: 1
1 1 1N N
BYieldLoss N
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Experimental SetupExperimental Setup Commercial 90nm CMOS technology
Area overhead 838 two-input NAND equivalent gates
An industrial circuit [2]
Number of gates: 2.6M Number of scan cells: 274K Compressed scan test data volume: 106M
System parameters Flit injection rate: 0.25 flit per cycle Flit size: 32 bits Retransmission delay: 40 cycles
[2] C. Barnhart et al, OPMISR: The Foundation for Compressed ATPG Vectors.In Proc. IEEE International Test Conference, pp. 748-757, Nov. 2001
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Test Yield Loss for a Core with 2.6M GatesTest Yield Loss for a Core with 2.6M Gates
Yield Loss: 4.41%
Yield Loss: 0.05%
Cost: Testing Time Penalty: 0.15%
Yield Loss: 28.20%
Flit Error Rate: 10-7
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Proposed Technique vs. Buffer-Only SolutionProposed Technique vs. Buffer-Only Solution
λYield Loss ≤ 1% Yield Loss ≤ 0.5%
nb (flits) np (flits) ΔTp nb (flits) np (flits) ΔTp
1x10-8 20 20 0.0003% 20 20 0.0003%
5x10-8 40 20 0.0006% 40 20 0.0009%
1x10-7 40 20 0.0018% 40 20 0.0033%
5x10-7 100 20 0.0411% 120 20 0.0824%
1x10-6 160 20 0.1642% 180 20 0.3297%
λ: Flit error rate nb: Buffer size for buffer-only solution
np: Buffer size for the proposed design
ΔTp: Testing time extension ratio of the proposed design
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ConclusionConclusion
The “error-free” assumption of existing work is questionable
Fault-tolerant schemes may lead to traffic jitter and variable test bandwidth
We propose a “jitter-aware” test wrapper“jitter-aware” test wrapper and an on-chip “jitter-transparent” ATE interface“jitter-transparent” ATE interface to achieve reliable modular testing
Experimental results demonstrate the effectiveness
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Thank you !Thank you !
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Timing Diagram of Test WrapperTiming Diagram of Test Wrapper
11 12
Scan_En
OCP_Clk
Scan_Clk
Gated_Clk
MCmd_In
SCmdAccept_In
Block_Ctrl
IPath_Blocked
Mdata_In
A B C D EShift Capture Halt