Growing complexity of high-speed data networks in vehicles requires multidimensional testing
by Thomas Zirngibl, M.Sc., Team Leader Cockpit Electronics at ARRK Engineering
Highly and fully automated driving systems have long since ceased to be fiction, but rather represent the future prospects of the automotive industry. In particular, for driving and safety-relevant components such as engine control units, lane departure warning systems and infotainment systems, it is essential to transmit large amounts of data both quickly and absolutely reliably. This is because display or communication failures – for example in navigation systems, parking aids or even indicator lights/telltales – can lead to dangerous situations for the driver and even accidents involving several people. For this reason, automotive manufacturers are already using high-speed data transmission via Automotive Ethernet to network individual control units with each other and with the system network as a whole. In the course of increasing high integration, the future use of Automotive Ethernet as the main bus system is also coming within reach. However, in order to cope with this growing complexity from a safety perspective, existing test methods are no longer sufficient, as they only focus on individual system components and disregard systemic verification. To counteract this weakness, testing strategies for Automotive Ethernet must in future be able to capture the increasingly complex interactions between the individual protocols and ECUs.
To keep the increasing number of control units for assisted and autonomous driving within manageable limits in the course of this development, an increasing degree of integration of the systems in the vehicle is also necessary, so that fewer ECUs (electronic control units) perform more functions overall. The aim of the high integration is to save costs and weight, but this subsequently leads to a proportional increase in software complexity in the system. At the same time, the number of Automotive Ethernet protocols is also increasing (see fig.1) to meet the ever-increasing software requirements. “In order to ensure the continued reliable functioning of systems networking together via Automotive Ethernet, especially highly automated driving systems, it is therefore essential to also adapt the test methodology to the growing complexities,” says Harald Faltheiner, Development Engineer Hardware and Systems Engineering at ARRK Engineering GmbH. “This is because growing networking also increases the interactions between hardware and software layers, which have simply received too little attention to date.”
This discrepancy is due, among other things, to the fact that the Ethernet systems developed since the 1970s in the consumer and business segments differ from automotive Ethernet primarily in the area of the physical layer. This is because while many already established standard protocols, such as TCP/IP, UDP and the IPvx protocols, could simply be adopted or adapted accordingly for use in the automotive industry, the automotive industry places significantly higher demands on the networking technology in terms of hardware, which standard Ethernet with its shielded twisted pair cables cannot fulfill. Automotive Ethernet must withstand a high temperature range – typically up to AEC-Q Grade 1 (-40 °C to +125 °C) – as well as extreme mechanical loads, comply with strict EMC limits, have the lowest possible power consumption in standby mode and also be cost- and weight-efficient. These and other requirements have been achieved over the past ten years through a large number of measures involving adjustments to the hardware and software.
“In order to contain these existing gaps in the testing of vehicle networks, which are growing with increasing complexity, ARRK Engineering has developed a test methodology that covers the entire system from a comprehensive perspective,” explains Faltheiner. The first step of this solution approach is the introduction of an interaction analysis; both in existing and new tests. In this way, control units are not only to be tested in isolation, as is customary with suppliers or manufacturers, but also with regard to their functionality in the system network. In doing so, the specialists at ARRK Engineering basically assume that there are protocols that can lead to malfunctions when interacting with each other. Secondly, the system is specifically loaded so that the probability of unwanted interactions occurring between the control units and the protocols increases. It is essential to apply or change several parameters simultaneously - such as the sum of the functions executed, the voltage, the number of protocols or the timing - and to record and track every step of the test procedure in detail (see fig 2.). On the one hand, this is the only way to define appropriate criteria for evaluating a test as “failed” or “passed”. On the other hand, this ensures that a specific failure, such as the failure of a display system, can also be traced back to a concrete trigger within the system complex.
Automotive Ethernet as the networking system of the future
While in most cases today a system architecture with domains and a central gateway is still used and can only be implemented as a subsystem within the Automotive Ethernet, the so-called zone-based architecture (see Fig. 3) is already coming within reach in the course of high integration. This flexible and scalable concept allows networking to take place at the core via Ethernet switches, which forward all the signals. Automotive Ethernet is an adequate networking technology for the zone-based architecture. In principle, there is the possibility of establishing Automotive Ethernet as a system bus sooner or later in the context of increasingly automated driving systems. "In this context, we can assume that the release rate of new protocols for Automotive Ethernet will continue to increase," notes Faltheiner. "Therefore, it is particularly important to consider the corresponding testability already in parallel with the protocol development and to release both - protocol and test specifications - at the same time." To address this constant need for further development, ARRK's engineers pay explicit attention to its future viability in their comprehensive test methodology, so that strategies and concepts can be easily adapted and extended to take into account new protocols.