Automotive design: Fill hardware-in-the-loop gaps

Automotive control systems developers focusing on powertrain, HEV/EV and chassis/safety applications have an increasing need to accelerate and improve their development process as to ensure they can deliver high quality and reliable software on time. In order to identify opportunity for improvement in the development process, we need to look at the current approaches used in the development of such systems and identify potential gaps and solutions. In this post, we will focus on model-based design through the use of Hardware-in-the-Loop systems.

Figure 1 highlights four currently used 'in-the-loop' technologies.

Let's review these technologies in the context of HW/SW development concerns.

Model-in-the-loop (MIL): model-in-the-loop provides an approach to validate control strategy and algorithm in a simulated environment. This can be done early and tools such as Simulink and SABER have been used extensively in this area. From a HW/SW perspective, there is however no execution of either the embedded software code or the actual microcontroller on which the code will execute.

Software-in-the-loop (SIL): software-in-the-loop provides the ability to use a software representation of the control strategy and algorithm. In this case the software executed is a partial software representation and is compiled for execution on the host PC target. As a result there is no concept of the embedded hardware to be used in the final electronic control unit (ECU) product.

Processor-in-the-loop (PIL): processor-in-the-loop focuses on the use of an evaluation board connected to a host PC executing a plant model. In this context the embedded software is compiled for architectures comparable to the final MCU. PIL still focuses on the control algorithmic implementation, just as MIL and SIL do.

MIL, SIL and PIL can be used early in the design, however they each have limitations when it comes to HW/SW and focus primarily on the control algorithm development and implementation.

Hardware-in-the-loop (HIL) provides the combination of executing the embedded software on the actual ECU hardware in combination with a model of the physical system (plant). Although this seems like the right environment, transitioning to a HIL environment requires a significant effort, thus creating a gap in the development flow as shown in figure 2.