x-alignment techniques for improving the observability of response compactors ozgur sinanoglu sobeeh...
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X-Alignment Techniques for Improving the Observ-
ability ofResponse Compactors
Ozgur Sinanoglu Sobeeh Almukhaizim†Math & Computer Science Department Computer Engineering Department
Kuwait University Kuwait [email protected] [email protected]
2010 년 10 월 16 일김인수
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Purposes of this paper
• Improving the observability of response compactors.
• Enhancing fault detection per test pattern.
• Making room for more test patterns in the tester memory.
– Propose X-Align technique.
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Properties of X-alignment tech-niques
• X-alignment hardware is fixed for a given de-sign and is independent of any test set and any fault model.
• X-alignment hardware can be reconfigured based on any given set of test responses.
• X-alignment techniques can be utilized in con-junction with any response compactor to ma-nipulate x-distribution in favor of the compactor
• X-alignment hardware has a small area over-head and its insertion can be seamlessly inte-grated into the conventional design flow.
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Response compaction tech-niques
Vertical Compaction Methods
Horizontal Compaction Methods
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XOR-based V-compaction
• XOR-based compaction with two parity trees
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XOR-based V-compaction with V-align
• Delaying shift-out operations in two scan chains for aligning x’s
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• Vertical Align block
ΔMAX (maximum allowable delay) = 3
XOR-based V-compaction with V-align
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Vertical Alignment of X’s
the transformation of the scan response into a map of known and un-known bits.T(c, δ) := 1 if(δ − 1)th cell of cth chain = x,
0 otherwise 0 ≤ c < num_chains, 1 ≤ δ ≤ depth
the definition of the solution variables.
dc := 1 if cth chain is delayed, 0 otherwise 0 ≤ c < num_chains
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if the scan slice i is observable:
s0 = (d0 + d0) ∧ (d1 + d1) ∧ (0 + d2) ∧ (d3 + d3) = d2
: AND clause
s1 = d1 ∧ d2 ∧ d3
s2 = d0 ∧ d1 ∧ d2 ∧ d3
s3 = 0
s4 = d0
Slices :
d0 = d2 = 1, d1 = d3 = 0s1 = s4 = 1, s0 = s2 = s3 = 0
Vertical Alignment of X’s
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XOR-based H-compaction with H-align
• Horizontal Align block
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Horizontal Alignment of X’s
the rotation of scan slices into a map of known and unknown bits.
T(c, δ) := 1 if δth cell of cth chain = x, 0 otherwise 0 ≤ c < num_chains, 0 ≤ δ ≤ depth
the definition of the rotation variables.
rδ := 1 if δth chain is rotated, 0 otherwise 0 ≤ δ ≤ depth
does not increase the scan depth
rotate direction : upward
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if the scan chain i is observable:
c0 = (r0 + r0) ∧ (r1) ∧ (r2) ∧ (r3) = r1 ∧ r2 ∧ r3
: AND clause
c1 = r0 ∧ r1 ∧ r2
c2 = r0 ∧ r1 ∧ r2
c3 = r1 ∧ r2 ∧ r3r1 = 1, r0 = r2 = r3 = 0c1 = c3 = 1, c0 = c2 = 0
Chains:
Horizontal Alignment of X’s
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2D-alignment
• Vertical Alignment
• Horizontal Alignment
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Without Alignment(Obs = 0)
With h-align Only(Obs = 8)
With v-align Only(Obs = 6)
With v-align After h-Align(Obs = 10)
2D-alignment
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• A clear advantage of aligning x’s in both directions (regardless of the or-der) is that the observability level of the 2D-alignment is guaranteed to surpass, or be equal to, that when x’s are aligned in one direction only.
2D-alignment
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Response Shaper
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X-Alignment: Random Responses
Px : unknown probability
# of observable scan cells
ΔMAX = 1
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A, B : two industrial circuits(provided by Cadence)80X196 : 80 scan chains with a scan depth of 196
# of observable scan cells
ΔMAX = 1
X-Alignment: Industrial Responses
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COST COMPARISONS ON ISCAS89 CIR-CUITS
TDV : Test data volume of the base case includes those of uncompressed stimuli and uncompacted responses.
The reported area costs for x-align and response shaper do not include the cost of the XOR tree.
20 CHAINS, SINGLE XOR TREE