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A Data Flow Fault Coverage Metric For Validation of Behavioral HDL Descriptions

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Title: A Data Flow Fault Coverage Metric For Validation of Behavioral HDL Descriptions


1
A Data Flow Fault Coverage Metric For Validation
of Behavioral HDL Descriptions
  • Qiushuang Zhang and Ian G. Harris
  • Dept. of Electrical Computer Engineering
  • University of Massachusetts, Amherst
  • qzhang_at_ecs.umass.edu, harris_at_ecs.umass.edu

2
Motivation
  • Verification is a bottleneck in system design
  • - Huge costs
  • - Increasing time-to-market
  • Simulation-based Validation is the predominant
    verification method
  • - Manually or randomly generate test vectors
  • - Lack of measurement of confidence

We propose a new metric to measure adequacy of
test vectors
3
Outline
  • Overview of system design flow
  • Introduce data-flow coverage metric
  • Present our data-flow metric approach and results
  • Conclusions and future work

4
System Design Flow
Our focus
5
Coverage Metrics
  • Coverage metrics measure the degree of validation
    achieved
  • Coverage metrics guide the test vector generation

6
Current Coverage Metrics
simple
  • Code based coverage
  • - Consider designs as a set of statements
  • Structural based coverage
  • - Consider designs as control and data flows
  • FSM based coverage
  • - Consider designs as FSMs

complicated
7
Data Flow of HDL Descriptions
Process Begin
  • PROCESS BEGIN
  • Wait until clockevent and clock 1
  • If (B 0) then
  • Zout lt P Q
  • Else
  • Zout lt P Q
  • End if
  • If (A 0) then
  • P lt C D
  • Else
  • P lt C D
  • End if
  • END PROCESS

1
2
3
5
7
8
10
End Simulation Cycle
End Process
8
Definition Use Occurrence
  • If (B 0) then
  • Zout lt P Q
  • Else
  • Zout lt P Q
  • End if
  • If (A 0) then
  • P lt C D
  • Else
  • P lt C D
  • End if

Process Begin
1
2
Pu
Pu
3
5
Definition Occurrence A statement where a value
is bound to the signal or variable. Use
Occurrence A statement which refers to the value
of the signal or variable.
7
8
10
Pd
Pd
End Simulation Cycle
End Process
9
Definition-Use (du) Pairs on Data Flow
Process Begin
Definition-Use (du) pairs
  • 8 ? 3

1
2
Pu
Pu
3
5
7
8
10
Pd
Pd
End Simulation Cycle
End Process
10
Definition-Use (du) Pairs on Data Flow
Process Begin
Definition-Use (du) pairs
  • 8 ? 3

1
  • 8 ? 5

2
Pu
Pu
3
5
7
8
10
Pd
Pd
End Simulation Cycle
End Process
11
Definition-Use (du) Pairs on Data Flow
Process Begin
Definition-Use (du) pairs
  • 8 ? 3

1
  • 8 ? 5

2
Pu
Pu
  • 10 ? 3

3
5
7
8
10
Pd
Pd
End Simulation Cycle
End Process
12
Definition-Use (du) Pairs on Data Flow
Process Begin
Definition-Use (du) pairs
  • 8 ? 3

1
  • 8 ? 5

2
Pu
Pu
  • 10 ? 3

3
5
7
  • 10 ? 5

8
10
Pd
Pd
End Simulation Cycle
End Process
13
Requirement of All du Pairs Metric
  • Definition clear path w.r.t. signal or variable
    X A path in the flow graph without definition
    occurrence of X.
  • Requirement Definition clear paths from every
    definition to every use of the same signal or
    variable are executed by test vectors.
  • Example For signal P, 4 du pairs are required to
    execute.
  • 8? 3, 8 ? 5, 10 ? 3 and 10 ? 5.

14
Why All du pairs?
xd x in1 ? x 2 in1 (fault)
xu1 if (x 0) then
xu2 else if (x lt 3) then xu3 y
lt x y else
end if
  • d-u1 cannot detect the fault
  • d-u2 may detect the fault
  • d-u3 can detect the fault.
  • Specific faults may not be detected by a
    particular use.
  • All du pairs requirement ensures that each
    definition is used in every context.

15
All du Pair Coverage Approach
  • Step 1 Identify all du pairs of the HDL
    description which are required to execute.
  • Step 2 Simulate the HDL description with
    candidate test patterns.
  • Step 3 The fraction of executed du pairs is the
    all du pairs coverage.

16
All du Pairs Coverage Results
  • All du pairs coverage is less than or equal to
    statement coverage.
  • There may be undetected faults associated with
    unexplored du pairs.

17
Conclusions and Future Work
  • Introduce the importance of coverage metrics for
    validation
  • Present our all du pairs metric approach and
    results
  • In future, improve the all du pairs metric to
    consider observability
  • Use results of all du pairs metric analysis to
    guide generation of new test vectors

18
Fault Coverage Metrics Comparison
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