The ARM-Linux IoT server is built based on the XSCALE PXA270 processor platform and the open source Linux system. The 51-chip microcomputer is used to connect peripheral devices such as temperature and humidity sensing module and LED lamp, and the Up-Tech embedded experiment box based on XSCALE PXA270 processor is used as the core server operation platform. Firstly, the communication design between ARM-Linux system setup, daemon and CGI program of embedded device is introduced. Then, the design and implementation of iQuery class library and AJAX technology used in Web server construction and network program design are introduced in detail.
The Internet of Things (IoT) is an extension of Internet applications. It is an emerging networking technology. Its core is the communication of information between objects and objects, and it is also the interaction control between objects. Internet of Things technology mainly uses various sensor devices, such as wireless technology, radio frequency identification (RFID) technology, various types of sensors and other technical devices to pass various information in the physical world, such as temperature, light intensity, location and other information through the network. Transmission, to achieve the purpose of information exchange between things and things.
To make it easy for people to access IoT information, monitor and control all types of sensor nodes and electrical equipment, a friendly user interface is a prerequisite. The B/S-based solution is the first choice for building systems with its client-side versatility. This paper will design and develop a general IoT server based on ARM processor platform and Linux embedded operating system. On the hardware platform, it will use UPTECH embedded development experiment box based on XSCALEPXA270 processor, 51 single chip microcomputer and various sensing controls. equipment. The ARM LinuX system is used on this embedded device, and the server is built under the embedded Linux system. The B/S architecture is adopted, and the BOA is used as the WEB server to realize remote information transmission and intelligent interaction through CGI communication.
1 system architecture
In order to highlight the low power consumption, low cost, high service level and high processing efficiency of the modern IoT server system, the server will run on the UP-Tech embedded device based on XSCALE PXA270 processor, and use 51 MCU to connect various transmissions. Sense control equipment.
The ARM Linux operating system with the 2.6.28 kernel was ported to the UP-Tech embedded device. On the Linux system, a daemon is written to communicate with the 51 MCU to communicate with various sensing control devices on the Linux system. The Boa WEB server is ported on Linux to build an interactive user interface. Enables users to view or control various sensing control devices in real time by accessing the page through a browser.
The system architecture is shown in Figure 1.
Figure 1 System Architecture
2 IoT data acquisition and processing subsystem design
2.1 Data acquisition system based on 51 single chip microcomputer
In the aspect of IoT terminal equipment, 51 single-chip microcomputers are used to connect through its rich external expansion interface and temperature sensor, humidity sensor, and LED lamp. The development mode of "C language + driver library" is adopted in the software. Through such a development mode, not only the development efficiency can be improved, but also the information collection and processing of multiple sensors can be well performed. In connection with the ARM-Linux embedded platform, the UART virtual serial port is used to communicate with the embedded platform.
The basic implementation functions of this system are as follows:
(1) connecting each sensing module, obtaining information transmitted by the sensor through the input and output interface and recording;
(2) Set a timer to collect information of each sensing device and control the state of the device within a specified unit time. Synthesize their information and status into a data packet and send it through the virtual serial port;
(3) Litong virtual serial port communication, detecting the control signals sent from the ARM-Linux platform at all times;
(4) Analyze the data packet transmitted from the serial port, check whether the data source is legal, and then control the single chip and each control module according to a specific control code.
2.2 Data Processing System Based on ARM-Linux Platform
ARM-Linux platform refers to the use of open source Linux kernel after tailoring to specific requirements, after cross-compilation to get a Linux kernel that can run on ARM processor, and also customize a Linux root file system, the entire system capacity is controlled in several hundred KB to tens of MB. The system is mainly composed of three parts: BootLoader, ARM-Linux kernel, and Linux root file system.
On embedded devices, the main data processing system is implemented by a daemon. The daemon is responsible for receiving and processing the information sent by the MCU; on the one hand, accepting the query control request from the WEB server.
On the IoT server side, the request from the client access is received and verified by the server, and the request query and control instructions are passed to the daemon. The daemon receives the request from the server, and then sends a request query to the MCU after verification. Control instruction.
The communication process of the daemon is divided into two parts. The first part is the daemon to inform the CGI program of the server to update the data. The second part is to send the instruction control to the daemon by the server CGI program, and the control program is executed after the daemon listens.
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