3 Advanced Model Validation
The model-validation capabilities of Reactis help engineers detect
bugs earlier, when they are less costly to fix.
A primary benefit of model-based design is that it allows the detection and
correction of system-design defects at design (i.e. modeling) time, when they
are much less expensive and time consuming to correct, rather than at system-implementation
and testing time. Moreover, with proper tool support, the
probability of detecting defects at the model level can be significantly
increased. In this section, we elaborate on the advanced model-validation
capabilities of Reactis that help engineers build better models.
3.1 Debugging with Tester and Simulator
Reactis Tester and Simulator support model debugging through the automatic
generation of test suites that thoroughly exercise the model under investigation
(Reactis Tester), and through the visualization of tests as they are executed
on the model (Reactis Simulator). One such usage scenario of Tester and
Simulator is shown in Figure 4. Since Tester’s
guided-simulation test-generation algorithm thoroughly simulates a model during
test generation, it often uncovers runtime errors. For example, overflows,
missing cases, and bad array indexes can be discovered. Note that this type of
error is also detected when running simulations in Simulink; however, since
Tester’s guided-simulation engine systematically exercises the model much more
thoroughly than random simulation can, the probability of finding such modeling
problems is much higher using Reactis.
|Figure 4: Debugging Simulink models with Reactis Tester and Reactis Simulator|
Tester-generated tests may be executed in Simulator, which offers a number of
useful model debugging features; some of these are illustrated in
Figure 5. The figure includes a screenshot of Reactis invoked
on a Simulink/Stateflow model of an automotive cruise control system. This
example is one of several example applications included with the Reactis
distribution. The main window in the figure depicts the model hierarchy on the
left and an execution snapshot of a Stateflow diagram from the model on the
right. Reactis allows the user to choose between three distinct sources of
input values when visualizing model execution:
Input values may be read from a Tester-generated test.
- They may be generated randomly.
- They may be supplied interactively by the user.
As depicted, input values come from Test 6 of a Tester-generated test suite. The
other model-debugging facilities illustrated in the figure are as follows.
- You may take forward or reverse execution steps when simulating model
- You may dynamically open scopes to view the values of Stateflow
variables or Simulink blocks and signals. An example scope, depicting how the
value of Stateflow variable mode varies over time, is shown. This scope was
opened by right-clicking on the mode variable in the diagram panel and selecting
- You may query the current value of any Simulink block or signal,
Stateflow variable, or C variable by hovering over it with the mouse.
- You may set execution breakpoints. In the example, a breakpoint has
been set in state Active. Therefore, model execution will be suspended
when control reaches this state during simulation, allowing the user to
carefully examine the model before continuing simulation. Simulation may
be resumed in any input mode, i.e. reading inputs from the test,
generating them randomly, or querying the user for them.
- As shown in the execution snapshot, the current simulation state of the
model is highlighted in green and portions of the model that have not yet been
exercised during simulation are highlighted in red for easy recognition.
|Figure 5: Reactis Simulator offers an advanced debug environment
for Simulink models.|
3.2 Validating Models with Validator
The advanced model-validation capabilities of Reactis are implemented in Reactis
Validator. Validator searches for defects and inconsistencies in models. The
tool lets you formulate a requirement as an assertion, attach the
assertion to a model, and perform an automated search for a simulation of the
model that leads to a violation of the assertion. If Validator finds an
assertion violation, it returns a test that leads to the problem. This test may
then be executed in Reactis Simulator to gain an understanding of the sequence
of events that leads to the problem. Validator also offers an alternative usage
under which the tool searches for tests that exercise user-defined coverage
targets. The tool enables the early detection of design errors and
inconsistencies and reduces the effort required for design reviews.
|Figure 6: Reactis Validator automates functional testing.|
Figure 6 shows how engineers use Validator. First, a model is
instrumented with assertions to be checked and user-defined coverage targets. In
the following discussion, we will refer to such assertions and coverage targets
as Validator objectives. The tool is then invoked on the instrumented model to
search for assertion violations and paths leading to the specified coverage
targets. The output of a Validator run is a test suite that includes tests
leading to objectives found during the analysis. Validator objectives may be
added to any Simulink system or Stateflow diagram in a model.
Two mechanisms for formulating objectives in Simulink models are supported:
Expression objectives are C-like boolean expressions.
Diagram objectives are Simulink / Stateflow observer diagrams.
Diagram objectives are attached to a model using the Reactis GUI to specify
a Simulink system from a library and “wire” it into the model. The
diagrams are created using Simulink and Stateflow in the same way standard
models are built. After adding a diagram objective to a model, the diagram
will be included in the model’s hierarchy tree, just as library links are
in a model. Note that the diagram objectives are stored in a separate
library and the .mdl/.slx file containing the controller model remains
Because of its sophisticated model-debugging capabilities, the Reactis tool
suite provides significant added value to the MathWorks Simulink/Stateflow
modeling environment. The great virtue of model-level debugging is that it
enables engineers to debug a software design before any source code is
generated. The earlier logic errors are detected, the less costly they are