25-04-2012, 05:11 PM
Design For Testability
DFTnew.pdf (Size: 324.91 KB / Downloads: 237)
Testability
• Controllability: The ability to set some
circuit nodes to a certain states or logic
values.
• Observability: The ability to observe the
state or logic values of internal nodes.
Usage of Testability Measures
• Speed up test generation
• Improve the design testability
• Guide the DFT insertion
SCOAP
• Sandia Controllability Observability Analysis
Program.
• Using integers to reflect the difficulty of controlling
and observing the internal nodes.
• Higher numbers indicate more difficult to control or
observe.
• Applicable to both combinational & sequential
circuits.
Costs Associated with DFTs
• Pin Overhead
• Area / Yield
• Performance degradation
• Design Time
⇒There is no free lunch !
Flip-Flop Selection Algorithm
• Identify all cycles
• Repeat
for each vertex
count the frequency of appearance in the cycle list
select the most frequently used vertex
remove all cycles containing the remove (selected) vertex
until (cycle list is empty)
! This is a feedback vertex set problem, a wellknown
NP-complete problem, hence heuristic is
used.
DFTnew.pdf (Size: 324.91 KB / Downloads: 237)
Testability
• Controllability: The ability to set some
circuit nodes to a certain states or logic
values.
• Observability: The ability to observe the
state or logic values of internal nodes.
Usage of Testability Measures
• Speed up test generation
• Improve the design testability
• Guide the DFT insertion
SCOAP
• Sandia Controllability Observability Analysis
Program.
• Using integers to reflect the difficulty of controlling
and observing the internal nodes.
• Higher numbers indicate more difficult to control or
observe.
• Applicable to both combinational & sequential
circuits.
Costs Associated with DFTs
• Pin Overhead
• Area / Yield
• Performance degradation
• Design Time
⇒There is no free lunch !
Flip-Flop Selection Algorithm
• Identify all cycles
• Repeat
for each vertex
count the frequency of appearance in the cycle list
select the most frequently used vertex
remove all cycles containing the remove (selected) vertex
until (cycle list is empty)
! This is a feedback vertex set problem, a wellknown
NP-complete problem, hence heuristic is
used.