Shulou(Shulou.com)06/02 Report--

"Software is engulfing the world, and all the functions realized by specific hardware in the past will now be realized through software." the traditional closed industrial control system, its functions realized through specific hardware will be replaced by software in the industrial Internet or industrial 4.0 era.

I. on PLC Virtualization

I have been watching the evolution of the current and future state of PLC virtualization, and the great thing about virtualization technology is that no other progress in IT over the past six decades has provided more quantifiable advantages than virtualization. Historically, the ancestors of PLC and PC were a family, and they both evolved from the relay era. Since IT has achieved great success in virtualization, why can't PLC, who is a member of the same family, enjoy the great advantages of virtualization?

It is worth emphasizing again that the PLC virtualization referred to in this article is by no means a software version of PLC or PLC software installed in a virtual machine. Software PLC or "SoftPLC" is actually a kind of failed product, which is only a failed product for control system manufacturers to try to integrate between control system and information system. They see the great benefits and success of the general information system platform, but it is a pity that the series of "SoftPLC" attempts launched failed to enter the market.

The PLC virtualization referred to in this article can be defined as follows: PLC virtualization is a system that decouples the traditional dedicated PLC hardware functions and uses software methods and general standard modular hardware to simulate or simulate systems that look and behave like specific PLC hardware. In essence, based on the special dedicated hardware environment of PLC, the best way to virtualize PLC is for PLC vendors to actively provide a virtualized version of PLC, that is, to embrace existing virtualization technologies. In essence, some PLC vendors will deploy virtual controllers to customers in order to reduce the cost of controllers or maintain the high performance requirements of controllers in some large projects. These controllers can run on commercial IT hardware environments. This is the result of PLC vendors virtualizing their controllers to adapt to IT virtualization technology. Generally speaking, these virtualized versions of the controller will not appear on the market, will not appear in the supplier's product catalog, and will not even have any product number.

Back to our first question, can PLC enjoy the huge advantages of virtualization? The answer is yes, of course. The reason why we can't see it is that everything must have its premise and soil for its birth and development, and so is PLC virtualization.

II. Prerequisites and soils for the development of PLC virtualization

The innovation of science and technology is always pushing the great wheel of the times forward. The development of PLC virtualization will eventually mature with the development of relevant software and hardware technology, social value and business model.

2.1. Developing Software and hardware Technology of PLC Virtualization

With the maturity of the software and hardware technology of virtualized PLC, for example, at the technical and engineering level, the simulation and simulation of PLC processor, ISA bus, various special hardware cards, network IO and so on can be realized through software. these basic capabilities constitute the technical prerequisite for the realization and development of PLC virtualization.

Hardware Reconfiguration and Software definition of 2.1.1.PLC

So, at present, how do we carry on the virtualization operation for PLC, and what technology is the industry trying to carry out PLC virtualization? In the old paper "Development trend of Industrial Control Systems-PLC Virtualization and Software definition", we describe the research projects currently being carried out by control system suppliers, including Siemens, who decouple the PLC execution environment from the Imando O module and standardize, modularize and virtualize the PLC execution environment. The logic of PLC is abstracted by software definition, and the implementation idea of software-defined network is used to realize the program development and management of PLC execution logic through an application program, and the application program defines the function of hardware PLC. That is, the logic control, program storage and IO module of PLC are separated, and the application program is used to realize the logic control part. From a technical point of view, this is a "hardware refactoring and software definition" for PLC systems. Hardware refactoring and software definition are based on higher-level, more abstract resource and data automation based on virtualization technology. The control system manufacturers try to overtake at the bend, directly reconfigure the hardware and define the software of the PLC equipment, and launch a new type of PLC equipment that can adapt to the industrial Internet or industrial 4.0 era to replace the adaptability of the traditional PLC equipment in the new era. In the old article "PLC of ALC-- Software-defined Architecture", I briefly introduced a series of transitional products launched by the industry based on the above research.

2.1.2. Virtualization of traditional PLC Devic

So why do control system vendors directly ignore virtualizing existing PLC devices and introduce new architectural forms of PLC devices? Is it difficult to virtualize existing PLC devices?

From the point of view of the feasibility of technical implementation, if we need to implement the virtualization of PLC, we need to do the following:

1. Be able to run virtualized PLC CPU on a common architecture

2. It can solve the problem of timeliness of switched Ethernet.

3. The dedicated hardware for PLC can be virtualized into standardized IO cards and run on the general architecture.

4. Be able to support current commercial power supplies, such as 220V

5. Commercial IO cards / controllers that can support redundancy.

That is, we need to run the dedicated part of the PLC architecture on the standard architecture through simulation or simulation. First we need to create a virtual PLC software container like a virtual machine and install the PLC into it. Like virtual machines, this virtual PLC software container has PLC special virtual hardware devices such as CPU, ISA bus and IO cards from specific control system vendors.

From the perspective of virtualization at the PLC processor architecture level, the first thing to solve in PLC virtualization is to run PLC CPU simulation and simulation through the architecture. As Siemens S7-400 has been widely studied and reversed by the community, this paper uses Siemens S7-400 PLC as an example. Siemens S7-400 uses two Infineon TriCore processors to run PLC processing logic. While the existing simulator QEMU supports the simulation and simulation of TriCore processors, does it mean that Siemens S7-400 can be run with QEMU? If Siemens is the official to do this, I believe that only Siemens R & D department to recompile the firmware of Siemens S7-400, or add specific Siemens S7-400 configuration file support for QEMU, you can run Siemens S7-400 in QEMU, I also believe that there will be such a similar simulator within Siemens. From the point of view of the implementation of external vendors, it is particularly difficult to implement because it is not known whether this architecture has been specially modified by Siemens, but it is technically achievable. If Siemens has specially processed and modified the Infineon TriCore processor of Siemens S7-400s, then when external manufacturers implement simulation and simulation of Siemens S7-400s in QEMU, they need to build a new configuration file in QEMU that extends the existing QEMU TriCore configuration to adapt to the special modifications of Siemens S7-400s.

From the perspective of virtualization at the PLC ISA architecture level, S7-400 runs a virtual machine on top of the TriCore architecture. This virtual machine realizes the translation and conversion between Siemens machine code and processor machine code. In TriCore ISA, unconditional jumps begin with the machine code byte 0x1d, while similar unconditional jumps within the PLC virtual machine begin with the machine code byte 0x70 0x0b. The machine code in the virtual machine is called MC7. At present, MC7 has not appeared or leaked the firmware version on the public network, and it has not been fully mastered by external parties. Therefore, it is extremely difficult to realize the virtualization of ISA. Unless you find a good design that can solve the translation and transformation between them, and virtualize or reverse the translation and transformation through software. Or it can be solved by designing hardware-level ISA. This is somewhat similar to the binary translation technology, paravirtualization technology, and hardware-assisted virtualization technology in IT virtualization technology. However, due to the different standard designs of ISA from various PLC equipment manufacturers, it is impossible for a standardized ISA virtualization technology to completely virtualize the devices of most control system manufacturers in the world. In IT environment, these virtualization technologies are successful because the standard of IT hardware tends to be unified, and there are sufficient technical conditions to realize the translation and transformation of virtualization.

From the perspective of virtualization at the PLC runtime architecture level, we need to completely clone the S7-400 firmware into a QEMU image, and create and run the virtual PLC machine through the QEMU TriCore processor and the special S7-400 QEMU virtual machine configuration file. These virtual machine profiles include auxiliary hardware devices for the S7-400 (such as Ethernet and Icord O, etc.). However, due to the lack of relevant information, it is also difficult to obtain clones containing full firmware (including boot loaders and complete RTOS). Therefore, in addition to CPU and ISA, the construction of Siemens-S7-400 PLC virtualization also requires the construction of Siemens S7-400 auxiliary hardware devices (such as Ethernet and Imax O) configuration files.

To sum up, if we need to build PLC virtualization technology on top of the existing virtualization architecture, we need to solve a lot of problems, and for each PLC model of PLC system, we will build corresponding virtual PLC virtual machines and virtual hardware. The overall simulation or simulation process is shown in the following figure:

But given the large number of PLC models, trying to adopt this approach seems to be a thankless solution.

Pure Software Simulation of 2.1.3.OpenPLC

So there are no other PLC virtualization solutions? In addition to the steep technical route mentioned above, another way in the industry is to realize the software simulation of PLC through pure software, and open source OpenPLC is one of the typical representatives. The concept of OpenPLC also comes into being in the actual industrial application. In 1995, the power dispatching center of Maanshan Iron and Steel Company in China was faced with a problem. The power dispatching center had to monitor all kinds of energy and power signals from power plants, water plants, gas plants and power plants (responsible for power transmission). But these four data sources, including the pipe network for the transmission of energy and power, are incompatible with the control systems of hundreds of substations, booster stations and pumping stations. Some are still dedicated systems, not only there is no protocol, even developers have been unable to find. In addition to the communication incompatibility, even the control structures of these systems are quite different. The power plant is similar to the DCS structure, the waterworks and gas plants are the PLC structure, and the power plant is the SCADA structure. It is also difficult for the integrated staff to understand the system. In the end, the project was not solved with OpenPLC (not yet at the time), but the requirements of the project led to the birth of OpenPLC.

From OpenPLC's paper, OpenPLC puts forward the idea of designing a new type of open control system to solve the problem of interconnection of systems with different control requirements, which is common in process control and discrete manufacturing industry. Because the purpose of the system is to be suitable for all kinds of applications as much as possible, it is named open programmable control system, while English is Open Programmable Logic Controller, abbreviated as OpenPLC. The system was conceived in 1995 and its design idea was basically clear in 1997. Several main design principles are as follows:

1. OpenPLC should be a system based on PC technology, especially in situations that can give full play to the characteristics of PC (such as network, connection with the outside world, optimization, expert system, manipulation interface, data monitoring, document recording and printing, etc.). The work is undertaken by the PC-based system.

2. At the bottom, when highly reliable and real-time control is needed, it is borne by the distributed control system, but it is different from the fieldbus. It is not an instrument-based system, but a system-based system, the instrument or an ordinary instrument, only the Icano and the control unit are placed on the site, and the digital signal, not the analog 4-20mA signal, is transmitted back to the central control room, which requires that the original instrument is still available.

3. In the situation where the I / O points are concentrated, cabinets or racks similar to DCS or PLC can be used, and the internal modules can be connected by bus or network. The whole system should have high reliability, good compatibility and openness.

4. The system should be truly distributed, the front end can be centralized, and it can last hundreds of meters, several kilometers or even thousands of kilometers (on the other side of the earth). For this reason, the system must have TCP/IP-compatible protocols and WEB servers.

5. The scale can also range from a few dozen points to thousands or even hundreds of thousands of points. The increase in the scale of the system IPUBO should not lead to a major change in the system.

OpenPLC is an open source implementation that can simulate PLC on Linux and can be used on a general architecture. Implementing OpenPLC in existing virtualization technologies is simple because it can be easily compiled and installed on Linux and x86 architectures. The current OpenPLC has become increasingly mature after years of development, and has been gradually applied in some fields.

To sum up, no matter the new PLC virtualization based on the new "hardware reconfiguration and software definition", the virtualization based on traditional PLC devices, or the virtualization technologies such as OpenPLC implemented by pure software, all indicate that the development trend of PLC needs to be transformed and reborn under the new architecture. With the development of technology, the software and hardware technology maturity of PLC virtualization is close to the engineering application of products or technology solutions, and the conditions for building PLC virtualization begin to be available one after another, PLC virtualization will certainly come, but it is not necessarily called PLC virtualization, or it is a new concept at that time.

2.2. Resulting in great social value and business model

The advantages and benefits of the implementation of PLC virtualization technology are obvious, and I don't need to repeat them here. The huge social value and business model based on PLC virtualization technology is the inexhaustible source power of the industrial Internet or industrial 4.0 era.

The so-called huge social value means that from the user's point of view, the adoption of PLC virtualization enables any organization and individual to stand on the shoulders of giants to conduct business, avoid repeated rounds, greatly improve the efficiency of all aspects of software and service construction, and accelerate the architecture and landing of all kinds of applications, while the flexibility of resources enabled and expanded at will in the cloud can also save huge costs for enterprises.

The so-called great business model means that after the emergence of PLC virtualization technology, the products and services based on PLC virtualization are very suitable for the new era of industrial Internet or industrial 4.0. the core brain of standardized, modular, artificial intelligence and software-defined control systems greatly reduces the barriers for customers to enter. The stability, flexibility and convenience of technology infrastructure bring high customer stickiness, coupled with the scale effect that cloud computing and big data Center can bring, these factors make the Internet of things and industrial Internet based on PLC virtualization become a good business, corresponding to an excellent B-end business model.

III. Summary

PLC virtualization is not only successful at the business level, but also fundamentally changes the security architecture and security governance model of existing industrial control systems. Just like the advantages of traditional information system virtualization, PLC virtualization stack has unparalleled advantages in network security. We can build PLC network IO based on SDN network, through fine control of east-west network traffic, build fine full-flow detection, full-function forwarding and secure network links in "zero trust network" environment, and even build industrial security block system based on block chain. In addition, in the interior and front end of the PLC, we can calmly place and define the industrial control software firewall to protect the traffic entering and leaving the PLC. Therefore, the architecture of PLC virtualization will be more robust than current industrial control systems from the point of view of network security.

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