Marco Cereia

Performance of a Real-Time EtherCAT Master Under Linux

The adoption of open-source operating systems for the execution of real-time applications is gaining popularity, even in the networked control systems domain, due to cost and flexibility reasons. However, as opposed to their commercial counterparts, the actual performance level to be expected from them is still little known and may often depend on the kind of real-time extension being used, its configuration, and the overall software load of the system, including best-effort components. In this paper, an open-source EtherCAT master supported by a popular real-time extension for Linux, the RT Patch, is thoroughly evaluated with long-term measurements, which build confidence on the suitability of the proposed approach for real-world applications. Special attention is devoted to the unexpected, adverse effect that some best-effort components, for instance, graphics applications, may have on the overall real-time characteristics of the system. For reference, the proposed approach is also compared with RTAI, a more traditional and well-known real-time extension for Linux already in use for demanding applications.

A user space EtherCAT master architecture for hard real-time control systems

Recently, the open-source EtherCAT master developed by the IgH company, has been enhanced with the introduction of the EtherCAT library, which allows to develop control applications in user space. This feature makes it possible to build complex applications that need to use the floating point unit or existing user space libraries. Unfortunately, the EtherCAT library does not seem to be able to guarantee a high degree of determinism. In this paper, first the real-time performance of the user space implementation of the EtherCAT master is evaluated and compared with the one that can be obtained by implementing the same control application at the kernel level. Then, we propose an alternative hard real-time approach based on RTAI, that allows to exploit all the advantages of user space development, with a negligible impact on performance.

Performance evaluation of an EtherCAT master using Linux and the RT Patch

This paper has the twofold goal of investigating the real-time performance of an EtherCAT master entirely built from open-source components (using Linux and the RT Patch at the operating system level) and assess its ability to support concurrent best-effort tasks without compromising the real-time ones, depending on kernel configuration. This is especially important for the successful adoption of the proposed approach in real-world applications. A hardware-based data acquisition system enables measurements to be taken for long periods of time, and with high resolution and precision. At the same time, this method guarantees that the measurement process does not influence the behavior of the system under test in any way.

Experimental evaluation of the Linux RT Patch for real-time applications

The possibility of using Linux as underlying operating system for real-time applications has received considerable attention by industry due to several definite advantages, such as the lack of royalties and the availability of rich and programmer-friendly software development frameworks. In addition, the real-time capabilities of the Linux kernel have recently been enhanced considerably through the development of the Linux RT Patch. This paper evaluates the real-time characteristics of the Linux kernel with the RT Patch installed, in order to help the designer understand what sort of real-time performance is to be expected, and decide whether it is adequate or not for a given class of applications.

A software implementation of IEEE 1588 on RTAI/RTnet platforms

At present, an increasing number of distributed control systems are based on platforms made up of conventional PCs running open-source real-time operating systems. Often, the need arises in these systems to have networked devices supporting synchronized operations. In this paper, an inexpensive solution is introduced, described, implemented and evaluated that relies on standard software and protocols such as RTAI, RTnet and IEEE 1588. The main goals of this architecture are reducing design and development costs, ensuring adequate synchronization accuracy, and easing the porting of control applications to different H/W and S/W configurations.

Asymmetric virtualisation for real-time systems

The steady increase in performance of the processors commonly adopted for real-time systems leads to the opportunity of hosting diverse classes of tasks on the same hardware, for example real-time control tasks and a man-machine interface, each one under the control of its own operating system. This paper describes how an asymmetric virtualisation layer has been realised on top of the ARM TrustZone security extension, in order to support the concurrent execution of both a real-time and a general purpose operating system on the same processor. The resulting implementation has a small execution time overhead and does not require any modification to the general purpose operating system.

Latency evaluation of a firewall for industrial networks based on the Tofino Industrial Security Solution

Nowadays, industrial control networks are no longer conceived as isolated systems, being them exposed to the same kind of security threats affecting traditional office and business networks. For this kind of systems, the main security requirement is availability, thus the protection measures used to secure industrial control networks must take into account also performance aspects, such as latency and jitters, usually not critical in traditional networks. For this reason, knowing the delays introduced by devices used to protect the network is of paramount importance, in order to evaluate whether the timing constraints of the communication are still satisfied. This paper presents an experimental evaluation of the communication latency introduced by a firewall for industrial control networks built around the Tofino Industrial Security Solution. Experiments have been carried out in three main working conditions of the firewall, that is when 1) it is plugged in the network with all the protection modules disabled (decommissioned mode); 2) it implements basic security policies only; 3) it adopts complex filtering mechanisms allowing the deep inspection of Modbus TCP packets.

Security aspects of safety networks

The importance of safe communications in industrial environments has been steadily increasing over the past years and several special-purpose solutions have been developed to this purpose. However, the prevalent trend nowadays is the adoption of standard transmission technologies to support both safe and non-safe data exchanges over the same medium. This exposes safety-aware protocols to the same security threats experienced in conventional communication networks. This paper deals with some security aspects of a popular safety-oriented communication solution, namely Safe-tyNETp. Its main contribution is showing that safety protocols too suffer from security threats and can even make things simpler in carrying out certain types of attacks such as denial of service (DoS).

A MODBUS extension for inexpensive distributed embedded systems

The MODBUS protocol on TIA/EIA-485 is a proven fieldbus that provides client-server data exchange between industrial devices with minimal hardware requirements. However, a few aspects of the protocol are not adequate to fulfill the needs of a contemporary distributed embedded system, especially for what concerns address space size, guaranteed bandwidth allocation, and controlled handover between multiple masters. This paper shows how MODBUS can be extended, in a backward-compatible way, to address these shortcomings. The extension is very simple and does not require any additional hardware, hence it is suitable for inexpensive, distributed embedded systems. The proposed extension was implemented with little development effort, starting from a Commercial Off-The-Shelf (COTS) protocol stack, for which the source code is readily available.

System-level performance of an automation solution based on industry standards

The flexibility and reconfigurability requirements of factories and manufacturing plants of the future can be partially met by adopting technologies and solutions already available for testing and experimentation. Openness and adherence to international standards are becoming increasingly important in modern distributed production and automation systems, especially when they have to cope with ever-increasing product differentiations and short product lifecycles. However, the increased flexibility and openness should not come to detriment of the system real-time characteristics. This paper deals with a pilot mechatronic architecture for agile transport systems, which has been specifically developed to enable the study of the aforementioned aspects in the framework of the “Factory of the Future” Italian flagship project. In particular, the paper focuses on possible bottlenecks and pitfalls at the operating system and communication levels, and provides preliminary indications on how to address or mitigate them by means of solutions already available on the market.