An introduction to AUTOSAR layered architecture

DevelopmentCategory
8 min read
Harish Rajora

As you may know, the automobile industry is a leading employer in India. It makes up 35% of India’s manufacturing gross domestic product (GDP). This post addresses a facet of that industry that has grown in importance as consumers demand new digital services and experiences from their vehicles: AUTOSAR layered architecture (AUTomotive Open System ARchitecture).

AUTOSAR is a global development partnership whose goal is to standardize basic system functions and functional interfaces.

But first, a bit of history.

Before the year 2003, automobile manufacturers would instruct their vendors to build and ship electronic control units (ECUs) for them. These ECUs would be built based on the original equipment manufacturer’s (OEM) requirement, according to the purpose they would serve in the vehicle.

Since there can be more than 100 ECUs in a vehicle, the ECUs might not be similar always. The same process goes for another OEM who has hired another vendor to produce their ECUs and so on.

The problem with this approach is that it is good only till the point the relationship between OEM and the vendor ends.

If an OEM changes the vendor, they have to repeat the complete process of describing their ECU’s architecture and its working so that the new vendor can build acceptable ECUs. If the vendor changes the OEM, they might be asked to build ECUs that are doing the same job but are different in architecture.

All this leads to unnecessary expenses in terms of time and costs involved in the overall process. The chances of bugs also become high in such cases.

The solution to this problem is AUTOSAR layered architecture.

Introduction to AUTOSAR and its architecture

As you must now understand, ECU is an important part of the OEMs and previously different OEMs had different standards for the same. These issues are resolved by settling on a common architectural pattern.

This common architectural pattern started by BMW, Bosch, Continental AG, Daimler AG, Siemens VDO, and Volkswagen is called AUTOSAR architecture. Its current membership situation is as follows:

Core partners and partners of AUTOSAR architecture

This way, even if an OEM changes the vendor, it does not need to teach them their unique ECU architecture. An OEM can also tie up with another OEM for their software for some ECUs.

As all ECUs would have the same architecture, there is no need to rewrite the software again.

This is a layered architecture with three components:

  • Application layer
  • Runtime environment
  • Basic software (BSW)

Let’s analyze these three layers.

Components in AUTOSAR layered architecture

AUTOSAR layered architecture is made up of three layers.

DIfferent layers of AUTOSAR architecture

Application layer in AUTOSAR

The application layer is the topmost layer in AUTOSAR architecture. It is designed to work for specific tasks and execute the software components involved in that task.

For instance, dimming the light of the vehicle is something that the application layer handles.

Runtime environment (RTE)

The middle layer is the runtime environment layer that handles the communication part between various components. RTE takes care of communication between different ECUs, within the same ECU, between the basic software layer and application layer, etc.

RTE handles the tasks with the help of port interfaces that transfer data using data buffers.

Basic software (BSW)

The final and lowermost layer of AUTOSAR layered architecture is the basic software layer, popularly called as BSW layer.

This layer holds the responsibility of providing services to the AUTOSAR software components.

BSW contains modules standardized for functional use by the upper layer and structured into different layers that perform different jobs.

The modules are common to any other ECU working on AUTOSAR standards and hence make it easier to port or transport.

The microcontroller is the hardware part (not involved as a layer) that takes the instructions for processing further.

BSW layers and their tasks

BSW is an important layer with its own layered architecture underneath. Therefore we may need to detail it a bit more than its brief introduction.

As shown in the diagram above, the BSW layer is a structure of three components (or layers):

  • Service layer
  • ECU abstraction layer
  • Microcontroller abstraction layer

BSW - Service layer

The topmost layer of BSW is the service layer that remains unaffected by the bottom two layers’ work.

The main work of the service layer is to provide services from/to the application layer to/from the microcontroller.

These services vary in a wide range such as network services and memory services.

BSW - ECU abstraction layer

The second layer of BSW works on managing the ECU-related functionalities such as input-output or memory related etc.

This layer is called abstraction because it hides the low-level arrangement of ECU with the developer such as ports and hardware peripherals. It provides APIs that can access the ECU directly by calling them and connecting with the microcontroller.

BSW - Microcontroller abstraction layer

The last layer of BSW is the microcontroller abstraction layer, popularly called MCAL. Its responsibility holds with the hardware connection or simply the microcontroller. It holds the software for the drivers that connect with the microcontroller for further operations.

Since this is also an abstraction layer, it hides its low-level functionality and works independently from the upper layers such as application and RTE.

All these three layers of BSW make sure that the architecture is isolated and consistent across microcontrollers and ECU. Due to this, if any other software needs to be run on MCAL or another ECU is required, it can be done very easily.

AUTOSAR: Better software, lower costs

The main motive for shaking hands on a fixed standard is to increase portability and minimize costs.

If a vendor suddenly increases the price of ECU, why should companies bear the costs of shifting their methodologies to a new architecture or making new vendors adapt to theirs?

Porsche Turbo S dashboard

AUTOSAR eliminates these scenarios and provides a standard layered architecture followed by OEMs in their ECU communications.

To summarise, the primary benefits of AUTOSAR layered architecture are as follows:

  • Higher-quality ECU software
  • Lower development costs
  • No need to re-develop similar ECU software components repeatedly for the same applications

This post was all about AUTOSAR layered architecture and the layers underneath them as well. We tried to explore their working and impact on the overall system of microcontrollers and ECU.

I hope this post enlightened you about AUTOSAR and related technologies. Thank you for giving this post your valuable time.

The information contained in this blog post is provided for informational purposes only and should not be construed as an endorsement or advice from GoDaddy on any subject matter.

Frequently Asked Questions

Here we define a few concepts that will make the picture clearer.

What is an ECU?

An ECU is abbreviated for Electronic Control Unit or sometimes called Engine Control Unit with respect to automobiles.

An ECU is the brain of the vehicle, without which even the car’s engine would not ignite.

This device controls almost everything that happens inside a car. For example:

  • Airbag control during crashes
  • Maintaining the required temperature in the cabin
  • The ignition and the fuel injection into the engine

In earlier times, OEMs used a single ECU that could perform all the necessary operations alone. But as the vehicles improved and became more complex, you may find more than 100 ECUs with dedicated functions today.

This is a better strategy, as if one ECU goes down, the car would not stop (unless it is engine-related ECU).

What is a layered system architecture?

A layered system architecture is the most common type of architecture used in software development or electronics equipment development.

This is done to separate various components of the complete system according to their logic or working. A layered system architecture is made up of layers laid down horizontally one on top of another. Since these layers contain these components and separate them logically, the layered system architecture is often referred to as the “logical separation of the system.

Layered system architecture may look generally as follows (not necessarily relating to AUTOSAR):

Each layer in such a system holds a responsibility to perform. For instance, the presentation layer deals with a visual representation of components. So, all the components it holds are related to the same job.

Here, in the above image, you can notice the closed rectangle for each layer. This is done to represent the isolation of features. When we isolate these components, the debugging, development and maintenance become easier.

The layer may talk to the one above it (passing the data) or below it (receiving the data). There are no other connections between any other two layers, however.