What is the essence of the V model? Development of automotive software ECU subsystems

Too many people are talking about the V model, but the more common the concept is, the harder it seems to be to reach a consensus. This article gives my point of view.

There are actually many development models, such as incremental, prototype, spiral, fountain, W model, etc. Due to limited space and lack of necessity, we will not talk about so many.

In fact, the model that can reflect the most basic engineering logic is the waterfall. Most other models, including the V model, are derived based on the waterfall, and their shadow can be seen in some way.

Let’s start with the waterfall.

1 The waterfall model is a cognitive logic. The waterfall model is the model that everyone hears the most and it is also the model with the simplest cognitive logic.

The waterfall model, as the name suggests, advances layer by layer like the flow of water in a waterfall.

Simply put, it is an expansion on the three basic sections of requirements, design, and testing. Various engineering activities are arranged in order like dominoes and driven layer by layer until the last domino falls.

Although this method is simple, it is very easy to understand and therefore easy to manage. It is especially friendly to fields with high requirements for standardization and regularization, such as automobile manufacturing, which is a typical waterfall.

For the development of a simple, single software module, if the requirements are clearly described, the design method is determined, and the test cases are clear, the best approach is a single-wave waterfall.

Of course, waterfalls are not a one-way, single-channel, serial mode like a string of beads. Even the development of the simplest mechanical parts will have parallel, back-and-forth and repeated correction processes.

In general, we can summarize waterfalls in two broad terms:

Linear sequence on the timeline.

Subsequent inputs need to depend on previous outputs.

In this way, we will find that waterfall is not only a development model, but also a way of thinking that cannot be escaped.

2 The essence of the V model

However, the laws of the world are not always as perfect as the order of 12345. When we are faced with a system and cooperation environment with a certain degree of complexity, the most basic waterfall model is not convenient for us to refer to.

Cars, which have long supply chains and complex electromechanical hardware and software systems, face such problems. The V model evolved based on the waterfall has gradually become the most widely used model in the automotive industry.

Various system standards in the industry, such as AS PI CE, 26262, 21434, etc., are also based on the V-model architecture.

2.1 Nested Automobile V Model

The V model is usually considered a model for software development, but when it comes to automotive software, it is obviously impossible to talk about software independently.

We might as well understand it from the perspective of system engineering. When we look at the entire design and development of the car, we will find that it is an architecture of a large V model within a small V model.

First of all, multiple vehicle V models will serve as a background to support the overall development architecture of the car, and then support the achievement of vehicle milestone goals such as vehicle attribute definition, styling design, architecture design, demand splitting, subsystem implementation, sample delivery, vehicle integration, and vehicle verification.

Next, the development of each ECU subsystem is continuously advanced through multiple small ECU V models.

Furthermore, each ECU subsystem can be divided into disciplines such as mechanics, software, algorithms , calibration, hardware , and subsystem integration, and they also operate through the next level of small V model.

With the continuous iteration of the V model, components, subassemblies, functional domain systems and complete vehicles gradually mature until they reach the complete vehicle SOP.

2.2 V model core

So, what is the core of the V model? There are four points worth noting.

2.2.1 Layered and Blocked Refinement

We have to break things down and break them down for a better understanding, just like when we learn about matter, we have to dig deep into molecules, atoms, nuclei, protons, and quarks before we can understand it to some extent.

2.2.2 Pay close attention to verification and confirmation

The development of cars and car software involves a lot of verification at all levels. In a narrow sense, it is engineering testing; in a broad sense, all reviews, walkthroughs, milestones, audits, and test drives are part of verification and confirmation.

2.2.3 Division of labor and cooperation

The first point of stratification and refinement is also the premise of division of labor and cooperation. In turn, the mode of division of labor and cooperation also affects the level and architecture of the system. This is mutual. As Conway's law points out, " the product must be a microcosm of its organizational communication structure."

2.2.4 Start of Chaos

The problem now is that the V model divided into different "layers" and "blocks" is not the ultimate solution.

The automotive industry development ecosystem and the V model complement each other, and the V model has also become a skeleton in the booming automotive industry.

However, with the entry, domainization, and centralization of software, the hierarchical relationship from system to component has become increasingly weak, and the disciplinary boundaries between components have become increasingly blurred.

In real work, we often have conflicts about whether this is a system requirement or a software requirement, and we are entangled in whether this is software testing, hardware testing, or integration testing.

The chaos of the layered and chunked concept is becoming apparent.

Therefore, solving this chaos has become the current focus. It may take some time to restore order from chaos, but during this process, there is no need to rush to question the significance of the V model itself.

3 Summary of the full text In summary, this article provides 3 key information or viewpoints:

Waterfall is a basic cognitive and engineering logic.

Complex cars gradually move towards SOP through nested V models.

The characteristics of the V model are layered and block-based refinement, a strong focus on verification and confirmation, and division of labor and cooperation, but it is currently encountering the problem of layered and block-based chaos.

4 Conclusion In the chaos, we are most likely to be blinded by concepts, and everyone likes to be different. In fact, no matter what, we cannot get out of the most fundamental source of engineering - waterfall, and we cannot do without the core idea of ​​the V model. At least for now, it is still the basis for our understanding of automotive software.