Design of embedded remote monitoring system based on S3C2410

　　Nowadays, the networking and standardization of industrial control systems have always been a topic of great concern in the industry. For large industrial sites, due to the geographical dispersion of controlled objects, measurement and control devices, and the real-time requirements of control tasks, most control devices still remain in single-point local communication, with a short range of action and unable to achieve mutual integration with the enterprise information network. With the rapid development and continuous progress of computer, network communication and Internet technology, embedded systems have been increasingly widely used in many fields such as home and industry. How to connect embedded systems and embedded fieldbus-based industrial control systems to the Internet and use embedded systems as middleware to achieve remote management and control of FCS group control systems has become a research topic that people are paying more and more attention to.

　　The remote monitoring technology based on Web B/S mode has a very important feature: that is, as long as there is Internet access, users can log in to the server through the Internet to remotely monitor and manage the field equipment group. Starting from the networking of monitoring equipment, taking advantage of the field bus, embedded system and Internet technology, this paper designs an embedded remote monitoring system architecture based on B/S mode with high reliability and high security.

　　l Embedded systems and fieldbus

　　1.1 Embedded Systems

　　Embedded systems are application-centric, based on computer technology, and their software and hardware can be tailored. They are suitable for special-purpose computer systems with strict requirements on functions, reliability, cost, volume, and power consumption. Generally, embedded systems are composed of four parts: processor, memory, input/output device, and software (including operating system and application). Due to the penetration of Internet technology, embedded systems are becoming more and more intelligent and have more and more network-friendly features. The rapid development of Internet technology has provided an excellent way for embedded systems to enter industrial control. The application of embedded technology between field instruments and industrial equipment layers is the development trend of industrial monitoring systems, and the combination of embedded technology and Internet technology in field measurement and control systems makes it easy for the entire industrial control network to achieve seamless connection with the information network.

　　1.2 Fieldbus Technology

　　Fieldbus technology is to place a dedicated microprocessor into traditional measurement and control instruments to make them digital and intelligent. It uses twisted pair cables and other media that can be easily connected to connect various intelligent devices and control devices on site into a network system, and transmits data and exchanges information according to open and standardized communication protocols. It breaks through the relatively closed limitations of DCS, disperses the measurement and control tasks to the field equipment, and the upper computer is only responsible for monitoring and some complex optimization and advanced control functions. It relies on microprocessor chips with data acquisition, calculation, control, and communication capabilities to achieve thorough decentralized control of industrial production equipment through field digital instruments. It uses the scattered measurement points on site and the single point of the control instrument as network nodes, connects these points in the form of a bus, and forms a fieldbus control system.

　　Fieldbus belongs to the lowest level network system and is a network-integrated fully distributed control system. It distributes the basic functions of the original distributed DCS system field controller to each network node. To this end, the original closed and dedicated system can be transformed into an open and standard system, so that products from different manufacturers can be interconnected. It is an upgraded product of the DCS system. FCS simplifies the system structure, reduces costs, and improves the reliability of system operation.

　　2 System Structure Introduction

　　2.1 System Design

　　The entire structure diagram of the system is shown in Figure 1. In the production workshop, the entire equipment is connected and networked through the FCS system to form a unified equipment layer. The networking method is the RS 485 industrial bus. The middleware is an embedded system, which realizes mutual communication with the lower-level equipment by driving the RS 485 interface on the ARM board. At the same time, a small Web server is embedded in the embedded system to realize the reception and reading of the lower-level data.

　　The upper layer of the system is designed with a network interface that can be directly connected to the Internet, which can directly connect the system to the Internet information network. As long as an IP address is assigned to the embedded operating system, there is no need to assign an IP address to each production device after it is connected to the network. The entire underlying device is uniformly identified by the CGI programming using the address set by itself, which greatly saves the use of IP addresses.

　　As long as the remote client has access to the Internet, it can authorize the user to log in to the system through the IP address to monitor the entire production process and equipment related information. At the same time, the system also provides an interface for monitoring the production site, allowing front-line employees to intuitively understand and record relevant production information on site.

　　2.2 System Solution Analysis

　　The remote monitoring system structure of this solution adopts the B/S mode. Compared with the traditional C/S mode structure, the three-layer B/S system structure separates the application module and display function on the client side and puts it on the Web server as a separate layer. The client only needs to use a single browser, so that the load can be evenly distributed to the Web server, greatly reducing the pressure on the client. The B/S structure mainly utilizes the increasingly mature Web browser technology, combined with the browser's multiple programming languages ​​and Web technology, and uses a general browser to realize powerful functions that originally required complex special software to achieve, and saves development costs.

　　The whole system is a real-time embedded Linux operating system transplanted into the embedded system, and a Web server is installed to act as a middleware. After the underlying control network is networked through the RS 485 bus, the RS 485 bus is connected to the hardware end of the system, and the collected data and related information are placed in the Linux Web server, so that the embedded device and the underlying device can communicate with each other. Because it is not suitable to use PC as a server in some harsh industrial production sites, the use of ARM and other series of embedded systems has the characteristics of low power consumption, good stability, and high reliability.

　　3 System Hardware Platform
 

　　The system collects data and remotely monitors the oil tanks in the workshop. The selected embedded microprocessor must be able to work reliably in the production environment. The CPU selected for the embedded remote monitoring system discussed here is the S3C2410 processor. The S3C2410 is a 16/32-bit RISC embedded microprocessor based on the ARM920T core produced by South Korea's Samstmg Company. It is mainly used for high-cost-effective, low-power handheld device applications. The entire hardware block diagram is shown in Figure 2.

　　The core modules include CS8900, RS 485 bus interface, FLASH SDRAM, reset and clock circuits, etc. The main functions are industrial field information collection and communication with remote clients. Since the Linux operating system directly includes various network protocols such as TCP/IP, the difficulty of developing network protocols can be avoided by directly transplanting the Linux operating system on the platform. The system provides an RJ45 Ethernet interface for direct communication with the Internet. The system focuses on solving communication problems with the Internet and information publishing problems.

　　4 Design and Analysis of System Software Platform

　　4.1 Software Platform Design

　　The system is built on the Linux platform. In order to collect the lower-level data, a small embedded Web server Boa is installed under the Linux operating system. The corresponding web page and CGI program path are set by configuring the Makefile file of the Boa server. Considering the portability and stability of the code, the CGI programs in the system are all written in C language. These include: user login verification module, information reading module, remote control module, etc. The homepage can be activated by clicking on the browser to access it, thereby realizing the interactive function between the browser and the server. The interactive process of the CGI program between the browser and the server is shown in Figure 3.

　　After the user enters the IP address set by the system in the remote client browser, he can log in to the system homepage. At this time, the login username and password verification are required. When the server is confirmed, he will enter the monitoring main page of the entire system. The page displays real-time data of the production workshop instruments, serial port data transmission and other related information. The page also has a technician's operation password verification. After logging in to the Boa server, if the authorized user wants to set the corresponding parameters of the production equipment, a technician must confirm the password, that is, the remote operation can only be realized with the presence of a technician. This can avoid the adverse consequences of senior users' misoperation without understanding the production situation. It is also another manifestation of system security. Even if an illegal user enters the homepage of the system, it is impossible to remotely control the equipment without the technician's password. At most, he can only see some information about the production equipment. The system is protected again from external interference operations to prevent catastrophic operations from occurring, which plays a double protection role. Senior managers only have remote login passwords, and technicians only have operation permission passwords. Only after the two people confirm at the same time can the remote operation be realized, and the managers can set the production parameters of the system through this page. Displaying the monitoring interface in the form of a web page not only utilizes existing IT technology and saves the cost of purchasing and developing monitoring software, but also frees users from geographical restrictions, laying an effective foundation for realizing modern integrated manufacturing in enterprises.

　　4.2 Safety Performance Analysis

　　The embedded remote monitoring system replaces the traditional data acquisition mode of industrial computer plus data acquisition card and local monitoring mode, which greatly saves costs. Since the Linux operating system customized by the system developer is used as the core of the system's software platform, and the access control of objects such as files, directories, and processes in the Linux operating system is implemented by mandatory access control (MAC), it allows different users to only access object information related to them and within a specified range, fundamentally preventing the loss of information and access confusion. At the same time, the Linux operating system enables the system audit function to record security events that occur in the system, and audits various system log files, including general information logs, network connection logs, file transfer logs, and user login logs, to discover various potential security issues. Based on the Open Source strategy of Linux, most of the current popular computer viruses are targeted at Windows operating systems and MS-DOS, and there are fewer viruses targeting Linux systems. At the same time, coupled with the firewall that comes with the Linux system, the possibility of virus attack is basically eliminated, improving the security and performance of the entire system. The stability of the Linux operating system is recognized by everyone, which can ensure the continuous and long-term operation of the entire system. In terms of system maintenance, the system also has its great advantages: previously, a system had to be maintained by developers or specially trained employees. Now, anyone with maintenance authority can maintain this embedded remote monitoring system without any training. When the system fails or restarts after power failure, as long as the power of the embedded monitoring system ARM board is turned on again, the system will automatically load the program from the FLASH and boot into the Linux operating system. Since the command to automatically run the Web server is added to the Linux system startup file /etc/rc.loal, the system will automatically start the Web server and resume data collection and transmission. Because the system is solidified in the FLASH of the embedded system after testing, users can only read the system and cannot modify the system. In this way, even if a Windows-like virus appears, the virus cannot modify the written application, ensuring the high security of the system, so the possibility of system failure has been minimized.

　　5 Conclusion

　　The close combination of embedded technology and Internet technology will be more and more widely used in the field of industrial control, which is a new trend in the development of the new generation of control networks. The embedded remote monitoring system based on fieldbus can also be applied to other industrial monitoring and debugging systems and building monitoring systems of some intelligent communities. The system has the characteristics of high portability, simple structure, easy use, low power consumption, high reliability, etc., and has broad application prospects.