Configuration Management of the Model-Based Design Process 2007-01-1775

Configuration Management of the Model-Based Design Process 2007-01-1775
2007-01-1775
Configuration Management of the Model-Based Design
Process
Gavin Walker, Jonathan Friedman, and Rob Aberg
The MathWorks
Copyright © 2007 The MathWorks, Inc.
ABSTRACT
CONFIGURATION MANAGEMENT (CM)
Today, many leading automotive OEMs and Suppliers
are adopting Model-Based Design for the development
of embedded systems applications. In this paper, the
authors review the challenges of performing
configuration management that is adequate for use in a
production environment of the models and associated
files central to Model-Based Design.
A configuration can be defined as "an arrangement of
parts or elements." In this paper, we focus on those
parts or elements associated with Simulink models. By
managing the configuration of a model, we hope to
provide an example of how one might manage arbitrary
combinations of files as a configuration.
INTRODUCTION
A robust configuration management process allows
teams to manage the development and use of the
models within a large team project, including the various
model files themselves; the configuration of a model built
from many subcomponent models; and the model data
(parameters and signal specifications).
In addition to these traditional configuration
management requirements, within a production
environment a configuration management tool may be
used to store artifacts that document Model-Based
Design, including simulation results, test harnesses used
to verify the design (both inputs and outputs), generated
code and logs, and reports of formal coverage tests. To
ensure reproducibility, the system may catalogue the
work environment – that is, the versions of the OS,
modeling tools, compilers, etc.
Lastly, configuration management tools can be used to
manage the many model variants that are created to
capture both the different systems being controlled, as
well as the complexity of the controllers. For example,
on a given vehicle program, engineers may need to
develop controllers for luxury-, mid-, and base-level
vehicles, with differing requirements for the North
American, Asian, and European markets.
In this paper, the authors discuss how configuration
management tools can be used throughout ModelBased Design.
In particular, we aim to provide a mechanism that allows
us to easily define sets of files that are compatible with
each other, so that when other team members obtain
such a configuration of files from revision control they
are confident that the combination will work together.
This confidence can enable the sharing of work within a
company, and the parallel development of large Simulink
models. Additionally, by recording additional information,
or metadata, we aim to make it possible to extract from
the revision control system the precise set of files that
were sent to a supplier or customer, or which are simply
the latest good configuration of files.
We define a few terms before proceeding. In particular,
we avoid the term version and instead use revision.
•
•
•
•
•
Revision Control Software: Software that stores files
with unique revision numbers, and allows them to be
retrieved by name and revision number.
Repository: The place where the Revision Control
Software stores files.
Revision: A specific instance of a file stored within a
Revision Control Software tool.
Configuration: A collection of specific revisions of a
number of files that work together.
Root Model: We take a Simulink-centric view of
configuration management in this paper. We
assume that each project contains a root model,
which is the model that a user will open to begin
work on the project. This model may link to other
models.
An overview of a typical configuration management
process is given in Figure 1. We note the use of the
terms “check in” and “check out”, which we use in this
paper. Note that the meaning of these terms varies
between different revision control and configuration
management tools.
1
2
3
5
importantLibrary.mdl, revision 5, is not part of
the “current working” configuration, suggesting that it
is perhaps untested, contains a bug, or is simply not
compatible
with
the
latest
revisions
of
Project.mdl and newFeature.mdl.
6
Project.mdl
4
Figure 1: Steps in a typical configuration management
process.
1. Get a Configuration. Get a number of files, which
have been denoted as forming a mutually consistent
"configuration", from the revision control repository.
2. Create a File. The user creates a new file on his or
her local computer.
3. Add to Revision Control. Make the revision control
system aware of the new file. The only instance of
this file is on the user's local computer. It is not in the
repository. The user can still modify it.
4. Check Out. The user wishes to work on an existing
file from revision control. The instance of the file on
the user’s computer becomes editable. Other users
are made aware that this user is editing this file.
5. Check-In. Place the modifications made by the user
into the revision control repository. Give this file a
new, unique revision number to indicate that it is
different from its predecessors. The user's local
copy is no longer editable. This new revision is
available to all users.
6. Create a New Configuration. Label a number of
files as being a new, mutually consistent
"configuration". Other users can get this set of files
from the revision control system.
importantLibrary newFeature
.mdl
.mdl
Rev1
Rev1
Rev1,Rev1
Rev2
Rev2
Rev2
Rev3
Rev3
Rev3
Rev4
Rev4
Rev4,REV4
REV5
Rev5
REV5
Configurations: Project Creation – Italics, Release 1 -Bold, Release 2 – Bold-Italics, Current Working – ALL
CAPS
Figure 2: Illustration of revisions and configurations.
LINKING TO A CM TOOL
To implement confirmation management within ModelBased Design, we need to set up an interface from
MATLAB® and Simulink® to a revision control (RC) tool.
There are a number of ways to do this, which depend
upon the particular RC tool, the operating system that
the tools will be used with, and the sophistication
required from the interface.
The most straightforward way to put the files associated
with Model-Based Design under the control of revision
control software is to treat them as two separate tools.
The user will have access to the full functionality of the
revision control software through its standard user
interface. Why might that be suboptimal?
•
To clarify how we differentiate configurations from
revisions, consider the following example. We have a
project that consists of just three files: Project.mdl,
importantLibrary.mdl, and newFeature.mdl.
•
In Figure 2, we illustrate the development progress of
the project. We note the following points:
•
•
•
•
•
The first configuration, defined when the project was
created and denoted Rev1, contains only
Project.mdl,
revision
1
and
importantLibrary.mdl, revision 1.
The same revision of a file can appear in a number
of
different
configurations:
importantLibrary.mdl, revision 1 is part of both
the
“Project
Creation”
and
“Release
1”
configurations.
Some revisions of a file will may appear in any
configurations: for example, newFeature.mdl
revisions 3 and 4.
Configurations are being used here to denote major
events, such as external releases of the project, as
well to denote which is the current “good” set of files.
The
implication
of
Figure
2
is
that
Engineers have to use two tools, and remember to
use them. A common failure mode is for an engineer
to begin work in Simulink without checking out the
required files first.
Analysis can be performed within MATLAB and
Simulink to determine the dependencies of various
files upon each other. A third-party RC tool is
unlikely to understand such dependencies.
Having two separate tools makes it harder to
enforce a workflow and to guide the user to do the
correct thing. By writing a layer between the revision
control software and the Simulink models and
associated files, we can enforce such a process.
There are several available methods to link from
MATLAB into a revision control programs. The following
list is illustrative and is not meant to be exhaustive.
THE MICROSOFT SOURCE CONTROL COMMON
INTERFACE (SCCI) API
One published API for revision control is the Microsoft®
Source Code Control Interface (SCCI) API, supported on
Microsoft Windows. This API allows communication
between any revision control package and application
that implements the API. MathWorks tools use this
interface to perform basic revision control operations
directly from the MATLAB current directory browser,
from the Simulink file menu, and from the MATLAB
command-line.
Any source control package implementing this interface
on a Windows PC will appear in the Source Control
section of the MATLAB Preferences User Interface. For
a full description of this interface see the MATLAB
documentation section entitled “Source Control Interface
on Windows Platforms.”[1] A limitation of this interface is
that, to the authors’ knowledge, it does not support
tagging or labeling of a number of files to create a
configuration set.
CUSTOM INTERFACE TO REVISION CONTROL
TOOL
command line, by GUI-applications developed within
MATLAB, or using utility functions within MATLAB and
Simulink. A MATLAB GUI application might make
configuration management tasks more straightforward
by:
•
•
•
Providing a GUI-interface to common RC and CM
tasks
Using a GUI to guide users through the correct CM
process by enabling and disabling GUI functions as
necessary
Extracting information from RC tool and display it in
a user-friendly manner within Simulink, without
requiring the user to interact with, or have any
detailed knowledge, of the RC tool. This is illustrated
in Figure 3.
Many revision control packages publish an API that
allows other tools to interface to them directly. For
example, The MathWorks uses the published interface
into IBM® ClearCase® on UNIX platforms.
The advantage of such interfaces is that the full
functionality of the revision control software can be
made available. There are, however, disadvantages.
The client side interface has to be written from scratch,
and then maintained. The interface has to checked and
updated with each release (major, minor, or bug-fix) of
the source control tool. Such maintenance costs can be
high.
Figure 3: Automatically updated revision control
information available on a Simulink block.
HINTS, TIPS, AND COMMON STUMBLING BLOCKS
Setting up a source control tool to work with MATLAB
and Simulink is straightforward. We note the following
points:
•
•
•
Simulink .MDL files are stored as plain, ASCII, text.
Some revision control tools will automatically
attempt to merge changes to text files if two people
have edited the same file. This behavior may not
always be successful for Simulink files, and we
recommend setting the revision control tool to not
merge .MDL files.
Recall that MATLAB .MAT files are binary. Many
revision control tools will recognize them as such.
However, to ensure that the desired behavior, we
recommend setting the revision control tool to
explicitly not attempt to merge .MAT files.
Some older revision control tools may have
problems with MATLAB object directories – i.e.,
directory names that being with an “@” symbol. Most
can be configured to allow this. (The “@” symbol is
used in some CM tools for macro substitution.)
COMPONENT REUSE VIA REVISION
CONTROLLED PALETTES
The first step in using a revision control system within
Model-Based Design is to architect the model in such a
way that each controlled portion of the model has only
one primary owner or editor. To accomplish this goal,
one needs to create a balance to achieve a component
that is large enough to be useful but small enough to be
reusable. This task is by no means trivial and needs to
be supported by a process that allows for the evolution
of the components as content is added to the model
components. Once the model architecture has been
established, there are different mechanisms that can be
used to store and integrate the components.
USING SIMULINK LIBRARY LINKS
Consider the Simulink library shown in Figure 4. This
model contains a number of alternative implementations
of a particular control system. In general, this might be
just one of a series of libraries of useful components,
grouped by application or type.
APPLICATIONS FOR THE INTERFACE
Once an interface exists between MATLAB and Simulink
and a revision control or configuration management tool
many tasks can be performed from the MATLAB
We note that each of the subsystems in
control_palette_libs is itself a library link. Each of
these subsystems is stored in their own individual
Simulink libraries, thus achieving the goal of “one item of
functionality per file”. When a subsystem, such as
Analog
Control,
is
copied
from
control_palette_libs into a model, Simulink
follows the link back to the file where the subsystem is
actually implemented. Hence the model that the user
creates contains a link back to the library where Analog
Control is actually implemented, in this case,
AnalogControlLib.
Figure 5: Revision controlled "palette" using model
reference.
MODELS, DATA, AND ARTIFACTS
Figure 4: Revision controlled “palette” using library links.
This structure achieves two things:
•
•
An engineer can control what items go in the palette.
There might be many implementations of controllers
with revision control, but only approved ones end up
on the palette. The palette is itself within revision
control. (For example, in the illustration here, the
palette is at revision 1.1.)
The implementations of the individual control
algorithms are stored in libraries that contain just
one item of functionality. This allows each of the
control algorithms to be separately version
controlled. (For example, in the illustration here, the
palette is at revision 1.4.)
USING MODEL REFERENCE LINKS
An alternative to using libraries of libraries is to use a
library of model reference components, as illustrated in
Figure 5. If one of the Model Reference components is
copied from the palette into a Simulink model, then
subsequent analysis will show only a reference from the
item in the new model to the corresponding referenced
file. As for the implementation using library links, there
will be no references stored to the palette.
We recommend that Model Reference is used in
preference to library links to partition a large model into
components that are to be individually stored under
revision control.
There are many different answers to the question “What
do we need to store within a revision control system?”
The minimum requirement might be to store only the
files required to ensure that a new user getting only
these files from revision control would have a “fully
functional” model. The definition of “fully functional”
might change for a model as it progresses through a
typical Model-Based Design process. Initially it might be
sufficient for the model to simulate. Later it might require
additional files or libraries to support code generation.
To guarantee reproducibility at some point in the future,
or for future root cause analysis or similar activities, it is
common to additionally store “derived files” at specific
points within the development process, such as the
generated code, simulation or model validation results,
linearized approximations to a non-linear model, etc.
There can be additional benefits to storing files that
could, in principal, be entirely reproduced. For example,
when using Model Reference it can be useful add the
simulation target MEX to the configuration. When
another user gets the set of files from the configuration
management system they will not have to wait for the
MEX files to be rebuild. We note that if this is done then
a straightforward mechanism must be provided to allow
a user to ensure that these files can be made writable,
and hence rebuilt, if required. This is typical of the type
of trade-off that must be made between the often
conflicting demands of the complexity of a configuration
management system, the level of reproducibility it offers,
and the opportunity for additional benefits.
Other derivable files (“process artifacts”) relating to the
process, rather than the primary use of the models, that
might be stored include model checking reports used to
demonstrate review readiness, the code generation logs,
coverage reports, etc. The decision about what files to
store at what stages of the process will depend upon the
working practices of individual groups, companies and
industries.
To illustrate this concept, we use an MD5 checksum
algorithm. By generating checksums automatically
Exported on Sep.13,2006 14:41:57
Filename:
.sandboxroot
EngineModel.mdl
m20060908T182816.mdl
transmission.mdl
transmissionRatio.mdl
Rev.:
1.1.1.1
1.3
1.3
1.1
1.2
Checksum:
1e4f2a5e29cfc2806e7f758e99cf6a4b
afd710f2a2bdf3b32c046f1e539e9c88
2a36b6903e84662a65b8eb54688a6e56
9202b54deb6642f93e95cdb3fcb61c91
69949fe144b364035309c546c4f92531
(C)The MathWorks Inc. 2006
Figure 6: Checksum Manifest File
META DATA
In addition to the files we store, it is useful to also store
“meta data” with the configuration. Such information is
particularly useful for deciding which configuration to get
from the repository without actually having to get it. Most
revision control software automatically stores various
items of metadata, such as who last modified a file,
when they did it, and perhaps a comment about what
they did.
For a configuration management system to be relevant
to Model-Based Design we typically store more
information than this. What is stored depends upon the
task the models are being used for, the stage in the
development cycle, and can vary from company to
company. Some examples include:
•
Project status (e.g. “current working”, “release
candidate”, “delivered”);
•
Application suitability (“experimental”, “robustness
studies”, “fixed-step solvers”, “linearization”, “RapidPrototyping”, “Production Code”, etc.);
•
Classification (“internal use only”, “suitable for
export”, or “imported from customer”);
•
The version of The MathWorks tools used to
develop these files.
COMMON TASKS
A number of common tasks can be greatly enhanced by
making use of the additional information available when
a configuration management system is in use. We
describe some of the more common tasks.
CREATING ADDITIONAL INFORMATION FOR THE
AUDIT TRAIL: CHECKSUMS
It can be useful to add additional information to the
configuration to give future users confidence that they
have the same instances of the files as those that were
checked in.
before and/or after key steps, we can make this
information more trustworthy. For example, prior to
creating a release or exporting a configuration we might
create a manifest file, such as the one shown in Figure
6.
MD5 checksums can also be included, straightforwardly,
into model advisor reports, test reports, coverage
reports, etc., and even into the generated code and
header files (using a Real-Time Workshop® Embedded
Coder source code template). In this way, the
traceability of the files throughout an entire Model-Based
Design development process can be greatly
enhanced.[2]
CREATING VARIANTS
A common workflow, especially in the automotive world,
is to take a baseline configuration of a system, and to
then create variants of it by swapping components for
alternatives that implement the same type of
functionality, but that are suitable for a different
application.
Consider the example of a vehicle engine control unit
(ECU). One of the components of the ECU is the “idlespeed control” component. Suppose that the baseline
configuration of the ECU is suitable for a vehicle with
automatic transmission and a normally aspirated engine.
A later model of the vehicle has a manual transmission
and a turbo-charged engine. To configure the ECU to be
suitable for this new vehicle we might need to exchange
the idle-speed control component for one that is suited
to this new vehicle. We can do this by deleting the
Simulink subsystem that implements the baseline idlespeed control and replacing it with a more suitable
implementation. In doing so, we have created a new
variant of the original baseline configuration.
In reality, many components in the ECU would have to
be swapped to make the ECU suitable for this new
vehicle, and the creation of a variant may require a large
number of components to be swapped.
One way to enable the creation of variants within the
framework described in this paper is as follows:
The baseline model of the ECU is created. The various
alternative implementations of the idle-speed control unit
are created and tested. All the models are stored within
the same project. All the different idle-speed control
models are placed in a revision controlled palette, which
is also placed in the same project. The entire project is
marked within the configuration management system as
the baseline configuration.
When a new team member creates a local copy of the
project files to edit, often called a sandbox, from the
baseline configuration, he or she has all the files need to
create new variations. This user can check-out the ECU
model, replace the idle-speed control unit with one of the
alternatives from the revision controlled palette, and
hence create a new variation of the original model.
In a fuller implementation there might be many such
revision controlled palettes.
Part of the motivation of using a configuration
management system is to be able to trace the
development of a configuration, and to be able to
reproduce its outputs, whether it is generated code,
simulation results, linearized models, etc.
PARALLEL DEVELOPMENT OF LARGE
MODELS
It is possible to perform a top-down design within
Simulink. This workflow fits well with the Model-Based
Design philosophy of starting with simple models of the
parts of a design, and elaborating them with more detail
as the design evolves. This section suggests some
practical guidelines for this process.
previous
revisions
of
those
components
incompatible with the current and future
configurations.
However, the above discussion is not meant to imply
that interfaces should be set in stone. If an interface
chance is required to support new design requirements,
then the Configuration Management system can be used
to support the interface change and minimize the impact
on other team members.
Consider “Component A”, revision 1, used in Project 1
and Project 2. An engineer working on Project 1
changes the interface of Component A to make it
compatible with Component B, used only in Project 1.
Without CM: The engineer from Project 1 checks the
updated Component A, now at revision 2, back into
revision control. The next time that the engineers on
Project 2 perform a “get updates from revision control”
operation, they find that they have an incompatible
version of Component A.
With CM: The Engineer from Project 1 behaves as
before, but additionally creates a new configuration of
Project 1. Engineers on Project 2 check only for new
configurations of Project 2. They may be aware of the
new revision of Component A, but until an engineer from
Project 2 integrates it into their project and creates a
new configuration of Project 2, they will not get the new
revision.
GUIDELINES FOR DEFINING THE INTERFACES
We offer the following suggestions for defining the
interfaces of subsystems for a new project:
DEFINING THE INTERFACES
•
Defining the interface of a software component, whether
it is a C or M-code function, or a Simulink subsystem, is
a key first step for others being able to use it. There are
a number of reasons for this:
•
•
•
•
Agreeing on interfaces is an important first step in
deciding how to break down the functionality of a
large system into subcomponents. For example, if
every output from a component is an electrical
current apart from one signal, which is a pressure
signal, then this occurrence may suggest that the
component has missing functionality, such as a
model of a sensor that converts pressure to current,
or perhaps should not generate the pressure signal
at all.
Once component interfaces have been agreed upon
they can be developed in parallel. If the interface
remains stable then integrating those components
into a larger system is straightforward.
Changing the interface between components is
expensive. To do so requires changes to at least two
components (the source and receivers), and to their
test harnesses. An interface change also makes all
•
•
Base the boundaries of the subsystems on those of
the real systems. This guideline is especially useful
if a model contains both physical plant and control
system elements, and control elements run at
different rates.
Keep model elaboration in mind. For example, if the
development process requires the addition of sensor
models at a future step, one could start with an
empty subsystem that either passes signals straight
through, or performs a unit and/or name conversion
so that the sensor interfaces are captured.
Review the potential reuse of the component in
support of the current design and future designs –
some elements will have more ubiquitous reuse
such as “sleep state” feature.
Define and use a signal naming convention.
Within Simulink, the process of defining interfaces is
aided by appropriate use of Simulink Signal Buses, as
discussed in the Simulink documentation. [3]
DEFINING THE MODEL STRUCTURE
As far as possible, try to avoid a mix of implementation
detail and subsystems or components in the same level
of a model. This philosophy makes testing, and further
subdivision into subcomponents, straightforward.
scope of data for a given subsystem via the SubSystem
Parameters, Permit Hierarchical Resolution dialog.
Getting the right level of granularity for the components
of a model is important. We offer the following
guidelines:
DEFINING COMPONENT INTERFACES
•
•
•
•
Pick granularity so that only one engineer is likely to
need to edit each model at a time.
For interface definition, consider the suggestions
highlighted in the previous section.
Group by rate of update.
No decision should be set in stone. Components
can and should be subdivided as they increase in
size and complexity.
A BRIEF NOTE ON THE PARAMETERIZATION OF
COMPONENTS IN SIMULINK
In the following sections we discuss the various methods
for partitioning a Simulink model into a number of
components. We do not discuss the various methods of
partitioning the data that each of these components
requires. This topic could easily be the subject of a
paper in its own right. Instead, we highlight the following
points.
Global Parameters
A common approach in the automotive industry is to
completely separate the problem of parameter storage
from model storage. In this scenario, the parameters for
a model come from a database of calibration data, and
the specific calibration file used becomes part of the
configuration. The calibration data is treated as global
data, and resides in the base MATLAB workspace.
Non-Global Parameters
In this scenario, each component stores and loads its
own parameters. Various methods exist for storing such
local parameter data, and include:
•
•
•
Mask Workspaces, with or without the use of Mask
Initialization functions
With Model Reference, Model Workspaces
Using parameter files (.m or .mat) and callbacks of
the individual Simulink models (e.g., preload
function)
However, combining a number of components that store
their own parameter data runs the risk of parameter
name collisions. Specifically, if a naming convention for
parameters, or alternatively a data dictionary of unique
parameter names and definitions, is not used then there
is the risk that two components will use a parameter
having the same name but with different meanings.
See the Simulink documentation [3] for more information
on these features. Finally, we note that in Release
2006a from The MathWorks it is possible to control the
There are various ways in which signals can be passed
between different Simulink subsystems or components.
The choice of which method is the most appropriate will
vary from company to company, and project to project.
Picking the most suitable method requires trading-off
readability, robustness, and flexibility. We offer the
following suggestions.
Signal Buses
Signal Buses have been a standard feature of Simulink
for many releases. For more information on Signal
Buses, see the Simulink documentation.[3] Signal
Buses, especially when used in conjunction with Bus
Objects, offer built-in interface checking. Signal Buses
are particularly well-suited for use at the high levels of
models, where components often either
•
•
Have a very large number of signals going into, and
out of them; or
Do not use all the signals available.
An additional benefit of signal buses is that, should a
change in the interface definition be required, the
change can be performed by modifying the Bus Object.
As a result, one avoids the need to make structural
changes such as the addition or removal of ports and
signal lines to the model.
Inports and Outports for Each Signal
At the lower levels of a model, where the components
are specifications or implementations of algorithms the
use of individual inports and outports can improve
readability compared to signal buses.
We note that using ports to create interfaces has a
greater risk of connection problems, because it is difficult
to check the validity of connections, other than their data
type, size, etc.
CONCLUSIONS
In this paper, the authors have illustrated a number of
practical approaches to performing configuration
management within Model-Based Design. We have
discussed the different ways in which the files
associated with Model-Based Design can be linked to
third-party configuration management and revision
control packages, and the mechanisms within
MathWorks tools that allow large projects to be split into
a number of files suitable for use with such third-party
packages. Starting with features that are applicable to a
single user, we have discussed features and workflows
appropriate for small teams, through to those which are
appropriate for larger teams working in parallel on a
project.
REFERENCES
1. MATLAB Users Guide http://www.mathworks.com/access/helpdesk/help/te
chdoc/
3. Simulink Users Guide http://www.mathworks.com/access/helpdesk/help/to
olbox/simulink/
*The MathWorks, Inc. retains all copyrights in the figures and excerpts of
code provided in this article. These figures and excerpts of code are used with
permission from The MathWorks, Inc. All rights reserved.
©1994-2007 by The MathWorks, Inc.
MATLAB, Simulink, Stateflow, Handle Graphics, Real-Time Workshop, and
xPC TargetBox are registered trademarks and SimBiology, SimEvents, and
SimHydraulics are trademarks of The MathWorks, Inc. Other product or
brand names are trademarks or registered trademarks of their respective holders.
2. “Using MathWorks Tools to Generate Code for DO178B Applications,” Bill Potter, The MathWorks,
presented at The MathWorks Aerospace and
Defense Conference 2006.
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