Introduction to MBD and MBD model management

1 Introduction to MBD

Model-Based Design (MBD) is a project development method that revolves around model building. This method can avoid tedious code writing and debugging processes, and can greatly improve project development efficiency. In addition, it is more friendly to novices to learn automotive electronics from the perspective of models, and it is easy to learn and get started very quickly.

Searching for MBD related information on the Internet, there are many related technical blogs and posts, but many veteran engineers are not optimistic about MBD. In practice, it is mostly used by large companies and large projects, while small companies or small projects rarely use MBD development methods. The most widely used field of MBD should be the automotive electronics field, with many related products and tool chains. I will talk about MBD related products and companies separately in the future.

There is also an interesting phenomenon, that is, some engineers use part of the MBD development method, such as using HIL (Hardware In the Loop) for project functional testing, but code writing and debugging are still manually written. Of course, strictly speaking, HIL can be separated from MBD, and using HIL does not necessarily mean MBD.

There is another common development method called Rapid Control Prototyping (RCP). RCP is the opposite of MBD. HIL is to model the control object and download it to the real-time operating system. The controller used is the actual controller (which will become the product controller after HIL testing). In the RCP development process, the controller is a prototype controller, and the control object is generally the actual controlled object (it can also be a simulation object). The prototype controller and the final product are two different things, so RCP can only be used to verify software algorithms and cannot achieve product-level verification.

When mentioning HIL, it is inevitable to associate it with SIL (Simulation In the Loop), PIL (Processor In the Loop) and MIL (Model In the Loop). These three types of in-loop testing have a strong connection with MBD. If one or more of these four test methods (including HIL) are used in a project, and code generation is also used, then it can be considered that MBD is used. Of course, strictly speaking, the content of MBD is very rich, and here it refers to a very simple concept.

Specifically, the roles and practical applications of these four in-loop tests are as follows:

• SIL: This test is used to determine whether the automatically generated code can work properly. If the target code needs fixed-point processing, SIL will play a very important role. In addition, some of the generated code can even ensure that functional safety requirements (such as ISO26262) are met. If only floating-point operations are involved, the functions of SIL and PIL are very similar, and there is no need to perform SIL separately in this case;

• PIL: This test is used to determine whether the processor can meet the computing power requirements and data accuracy. However, in actual projects, computing power and accuracy will be fully considered in the early chip selection stage, and some experience can also determine whether the processor computing power and accuracy meet the requirements;

• MIL: This test is used to determine the feasibility of the algorithm. In fact, if the algorithm is not feasible, there will be no project. The biggest role of MIL is to sort out the development framework of the project. It is a design work at the system level. It can also learn unfamiliar fields or related knowledge.

• HIL: This test is used to determine whether the controller can work properly. The control object is usually a simulation model, but it runs in a real-time operating system. If the controlled object is not complex, HIL testing can also be performed with a real controlled object.

2 MBD model management

Here is a picture from MathWorks' Managing Model-Based Design to illustrate how MBD works:

How MBD works

If you have heard of it, you may have seen more of the V-shaped development process. We will talk about the V-shaped development process in detail later. Here we will mainly talk about how MBD works at a higher level.

Using the MBD method to carry out project development, the main process includes the following three points:

• Input: The input of MBD is requirements (requirements or specifications) and existing or public research results (Research);

• Model iteration: This is the core of MBD and the key to the efficient implementation of MBD. Model iteration involves the above-mentioned MIL, SIL, PIL, HIL and RCP. These are not necessary. You can just conduct corresponding tests according to the actual situation of the project.

• Output: automatically generated code, model report, test report, and verification report.

MBD has a very significant feature, which is that it can record and trace text records, so special tools are needed, such as the Simulink Requirements tool (there are also some other third-party tools). Models are created based on requirements, and each requirement has a corresponding model. At the same time, during the model iteration, corresponding model reports or test reports will be generated. Because all of this work revolves around the model, it is called model-based design.

The above three points contain a lot of content, which I will not discuss in depth here, because if I only describe them in words, it will be very abstract. In the future, I will combine examples to explain in detail what should be done in each link.

In fact, from my point of view, MBD is more like a project management method, not a development method. The object of our management is the model, which is iterated and tested. And tools like Simulink Requirements are also management tools. Under MBD, there are specific development methods, namely the MIL, HIL, etc. For engineers, they use development methods more, so MBD is equivalent to MIL and HIL. When implementing MBD, many teams do not care about model management issues, but only use development methods such as MIL and HIL, which may lead to poor final results, so some old engineers are not optimistic about MBD.