This paper mainly provides a new embedded remote communication mode through the SMTP protocol. That is, the SMTP protocol is implemented in the ARM processor and connected to the Internet through a twisted pair. The remote control device or instrumentation developed on the platform enables remote transmission of data over the Internet, and can be remotely monitored and controlled over the Internet on any computer connected to the Internet.
The project selected 32-bit microprocessor based on ARM architecture, introduced the components of the module, including ARM-based hardware structure model, software structure, SMTP basic structure and its operating mechanism. The detailed implementation and debugging process of the embedded SMTP software module in ARM system are analyzed in detail.
1. The overall structure of the systemIn the system, the SMTP server is introduced to the platform of ARM to implement the embedded SMTP server (Embedded SMTP Server). Based on this software and hardware system, the control equipment and instruments are developed, and the traditional test and control equipment is transformed into an Internet-based network test and control device with TCP/IP as the underlying communication protocol and SMTP technology as the core. Compared with the traditional SMTP Server, the embedded SMTP system simplifies the protocol structure and integrates information collection and information release into the on-site measurement and control equipment. Since SMTP is a standard cross-platform communication protocol in the Internet, the SMTP server embedded in the device can receive E-mail commands and data from any standard mailing tool. At the same time, due to the openness of the SMTP technology and the independent platform features, the design and maintenance workload of the software system and the communication system are greatly reduced, the personnel training cost is saved, and the management level of the field test and control equipment is improved.
1.1 system hardware structure
The core components of the system hardware consist of an embedded microprocessor system running an embedded operating system running the core software of the system on top of the embedded operating system. Due to the maturity of the ARM processor technology, the market share is high and the cost is drastically reduced. From the perspective of industrial control, we chose MOTOROLA based on the ARM core MX9328MX1. The chip is based on the ARM9T chip. On the one hand, it has the advantages of low power consumption and high performance of ARM processor; at the same time, it has rich on-chip resources, which is very suitable for the development of embedded products.
The hardware system includes a microprocessor that implements the SMTP communication function, which can be directly integrated with the front-end application system, or can be connected to the application system through the field bus. Including: 8M FLASH memory is used to store the real-time operating system kernel, TCP/IP protocol stack, various control programs and other parallel modules; 32M SDRAM memory is used for system operation; Ethernet interface is connected with Internet/Intranet The fieldbus expansion control module provides distributed control of equipment within a certain range of the site; general IO port control module. Its hardware structure is shown in Figure 1 [2].
Figure 1: Embedded SMTP remote control platform hardware structure
Considering the cost performance, the hardware structure of the system is adjusted according to the application environment, and the hardware resources are also limited. The system kernel of the real-time operating system, the TCP/IP protocol stack, and various applications must be written to the FLASH and loaded into the SDRAM at runtime, thus placing high demands on the software system.
1.2 system software structure
The software system of the whole system includes five parts: 1 embedded operating system; 2 virtual file system; 3 SMTP engine; 4 configuration module; 5 security module; 6 control program interface module.
The embedded operating system uses Linux as the software foundation of the system. Its excellent cross-platform portability, open source code, and configuration flexibility provide convenience for development. The built-in TCP/IP stack allows users to quickly develop applications for application layer protocols.
The virtual file system on Linux establishes a disk-like environment based on FLASH and SDRAM. The virtual file system uses data structures to store information such as file size, modification time, and so on. The control program and configuration text and the like required in the system are stored in the file system on the system chip through the virtual file system.
The SMTP engine is responsible for responding to user requests, allowing the user to remotely control the actions of the device through the application interface, threshold status reports, and periodically report the status to the user.
The configuration module enables the system administrator to set the parameters of the device by using the remote mail. The configuration environment variables defined in the system startup include the critical value of the device, the status report period, the network parameters such as the Socket port, the startup and stop time of the device, and the work cycle. Wait.
The configuration of network remote devices and access to control information are the focus of security protection. The security module protects sensitive information by defining a security domain on the server and a username/password defined for each security domain. Encryption measures can also be taken for request control actions and data to implement security protection. The system mainly implements protection measures through ESMTP. ESMTP is an extended SMTP protocol, which is a security authentication service provided by the mail server system to restrict the use of the system to distribute spam or other misconduct by official users of the system.
The application interface module implements control and data exchange of the embedded control system. In this system, the application program interface communicates with the embedded operating system, and the configuration, monitoring and control of the embedded system are realized by the driver of the device, which is the core of the system control. The monitor module is implemented using CGI (Common Gateway InteRFace).
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