Illustration: Design and Implementation of Embedded wireless LAN Devices

1 Introduction to Embedded Systems

Embedded systems are specialized computer systems that are based on computer technology, application-centric, software and hardware can be tailored, and have strict requirements on functions, reliability, power consumption, volume, and cost. Pursuing the goal of "short, small, light, thin, power-saving, fast, and low cost. Embedded system equipment has been widely used in manufacturing industry, process control, instrumentation, military equipment, consumer products and other fields. An embedded system consists of hardware and software. It is generally divided into five parts: processor, memory, input and output, operating system, and application software. 1:

The initial application of the embedded system was based on single-chip microcomputer. It only uses an 8-bit chip to execute some simple single-process programs without multi-process task scheduling. With the emergence of 16/32-bit embedded microprocessor, embedded systems are introduced into the embedded operating system, which frees application developers from small-scale development, it also provides a broader application space for embedded systems. The well-known embedded operating systems include ISI pSOS, WindRiver VxWorks, QNX, Microsoft WinCE, and open-source Linux and uC/OS.

Figure 1: Structure of the embedded system

2 wireless LAN Overview

Wireless Local Area Network (WLAN) is a short-range Wireless communication technology. It is a combination of modern computer networks and Wireless communication technologies. Transmit data, voice, and video signals in the Air Using Wireless RF or infrared Infra Red, IR technologies. In some special application environments, a wireless LAN can make up for the shortcomings of wired Ethernet composed of cables or optical cables to extend the network.

The standard physical layer of a wireless LAN defines two RF transmission modes and one infrared transmission mode. The RF method uses three frequency bands: The L frequency band is 902MHz ~ 928 MHz), S band GHz ~ 2.4835 GHz), C band 5.725GHz ~ 5.85 GHz ). Generally, the S frequency band is called the Industrial Science Medical frequency band, which is not restricted by the FCC of the US Federal Communications Commission. It belongs to the industrial free radiation frequency band. The wireless LAN working in this band has two Spread Spectrum methods: Direct Sequence Spread Spectrum, DSSS) and Frequency Hopping Spread Spectrum Frequency Hopping Spread Sprectrum, FHSS.

In June 1997, IEEE passed the wireless LAN standard, namely the 802.11 standard. The establishment of the IEEE 802.11 Wireless LAN standard is a milestone in the development of wireless network technology. The standard mainly defines the physical layer (PHY) and the media access control layer (MAC) of the network, the rules on the MAC layer are important.

The maximum speed of 802.11 is 2 Mbps, which cannot meet people's needs. The IEEE team also introduced the 802.11b standard. IEEE802.11b works in the 5.5 GHz band. It uses direct sequence spread spectrum DSSS technology and the compensation code-keycoded cosine modulation method. It can provide 11 Mb/s, Mb/s, 2 Mb/s, and 1 Mb/s speeds, it is compatible with at 2 Mb/s and 1 Mb/s rates. 802.11b is currently the most mature and widely used wireless LAN standard. This article is the IEEE-802.11b wireless network card.

Currently, the application of wireless LAN technology is limited to PCs and laptops, and is generally used in Hot Spot distribution. Embedded systems integrate wireless LAN technology to achieve wireless communication and data transmission will become a hot topic in future applications. For example, a wireless digital set-top box, computer, wireless network, and household appliances can form a home wireless LAN, which can be connected to the Internet through an AP, wireless router, or wireless bridge. wireless instruments can collect data and transmit data wirelessly; self-Organizing Network (Ad Hoc Network) is deployed on the work site for information transmission and remote wireless monitoring. This reduces wiring troubles and inconveniences and greatly improves industrial production efficiency, it is convenient for people to live.

3 Hardware Design of Embedded wireless LAN Module

This paper uses Samsung S3C2410X as an embedded microprocessor and wireless LAN technology to design an embedded wireless LAN device for data collection and wireless transmission. The hardware structure of the device is shown in figure 2.

Figure 2: system hardware structure

Nand flash is used to store startup programs, operating systems, TCP/IP protocol stacks, drivers, and related applications. S3C2410X supports nand flash Boot Loader. After the system powers on, S3C2410X loads the startup code from nand flash to the 4KB SRAM buffer called Steppingstone internally through the built-in nand flash controller to execute the startup task, instead of going through external SDRAM to start the system, This will speed up the entire system startup process. After the startup is complete, run the operating system. The code and subsequent applications are all executed in external SDRAM. After the operating system is started, you can execute the designed application, collect data through the RS232/485 interface, and then transmit data through the 802.11b wireless network card. All gpios of S3C2410X are introduced for future system function expansion.

1. Research and Test of Wireless LAN security technology
2. Single-Chip Solution for wireless LAN + Bluetooth Technology