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Virtual testing with model-based design
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By
Brett Murphy, The MathWorks
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Page 1 of 2
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Industrial Control Designline
(08/17/2009 10:18 AM EDT)
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Virtual testing, based on system simulation and Model-Based Design,
takes the traditional "test-at-the-end" system development process
(represented in the V diagram) and makes it more iterative. Virtual
testing shortens both the design cycle and the final physical testing
phase.
The Problems: System
Complexity and Late-Stage Error Detection
Complexity in embedded software development is driving the cost of test
and verification to as much as 70% of overall development costs.
Industrial automation, automotive, and aerospace engineers conduct
exhaustive design and code reviews and build increasingly complex test
systems to confirm that the software in embedded processors meets
high-integrity standards and design requirements. And as verification
consumes more time, engineers have fewer opportunities to innovate and
create product differentiation through design optimization.
Many organizations are finding that most errors they uncover in test
and integration were introduced at the beginning of the design process
while interpreting system requirements. Engineers now face the
challenge of checking for errors and "cleaning them out" closer to the
beginning of the development process, when they are cheaper to fix.
Finally, as development teams grow and become geographically dispersed,
they are seeking better ways to collaborate.
The Solution: Test Early
Embedded software errors can be cut substantially by doing more
complete design verification at or near the beginning of the design
process via systematic system simulation, or virtual testing. "Virtual"
in this case denotes simulation, but with no hardware involved—just
software and simulation engines. "Systematic" means building tests
based on requirements and then executing those tests against the system
design.
Two critical concepts that drive virtual testing process improvements:
- An executable system specification
- Requirements based tests
The executable system specification is a model that you can simulate,
and includes your system design as well as environment models: models
of the important elements of the physical world your embedded system
interacts with. The system model needs to include subsystem domains
such as controls, mechanical components, electrical components, and
hydraulics. These models should be as detailed as needed to capture
their system-level functional behavior.
Requirements-based tests are formulated from functional requirements
that can be expressed as tests; essentially, "Given a particular input,
here is the output I expect." At a minimum, you need to have a
simulation input signal or sequence for each test, as well as output
captured from the simulation, to compare with the expected output. You
should also build a complete set of tests that fully exercise the
requirements.
To understand how this works, consider the classic design process V
diagram (Figure 1). With virtual testing, you would follow a second V
early in the process, starting partway down the left leg and then up to
the right. The design flow moves to a virtual test rather than down the
left leg to the original apex (the point of implementation) and then up
the right leg (the hardware side) to physical testing.
Figure 1: The V diagram, which illustrates the
traditional
embedded system
development process. The right side represents physical test and
verification, which occur late in the process when problems are more
costly to fix.
(Click on image to enlarge)
Figure 1 illustrates a traditional design flow, in which engineering
teams move from written requirements to design, manual coding and,
finally, system integration and test. Ensuring requirements are valid
at the start is a challenge, verifying the design against the
requirements is difficult, and implementing the code is a manual,
error-prone process.
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