1 Introduction
Nowadays, there is an increasing demand for wireless communication in various industries, and wireless access to the Internet is one of the most important requirements. With the rapid development of information technology, embedded systems are rapidly and widely used in the industrial, service and consumer electronics industries. The XSCALE microarchitecture application processor is an embedded processor developed by Intel for a new generation of wireless applications. The CDMA 1X wireless communication network introduces high-speed packet data services and IP technologies, laying the foundation for supporting various multimedia packet services. CDMA 1X can provide a data rate of 153.6 kb/s. CDMA (Code Division MulTIple I Access) wireless network system has been put into use in the United States, South Korea, China and Hong Kong, China, and has achieved good network performance. Qualcomm, Nokia, Samsung, Sanyo Electronics and Siemens And other major companies in the world have carried out research and development of CDMA systems.
The development of embedded systems mostly adopts the idea of ​​modularization, which is first carried out on the development board, and then further developed according to the actual performance. XSBase is a high-end embedded device development platform based on Intel XSCALE PXA255 processor. It supports software and hardware development of embedded devices. We developed and implemented Intel XSCALE PXA255 high-performance embedded processor as the core hardware. The platform uses embedded Linux as the operating system, CDMA 1X wireless communication module YCIG-CCMG1X800 as the core communication unit, and embedded wireless communication access system supporting broadband wireless network CDMA 1X.
2 Embedded wireless communication terminal system overall description
The embedded wireless communication terminal system designed by us is a mobile wireless communication access system. Its location in the entire communication network is shown in Figure 1. It can wirelessly access the CDMA 1X wireless cellular network that has been spread all over the country. It can also access the Internet or PSTN (Public Switched Telephone Network) through the CDMA 1X wireless network. The wireless communication terminal system has a high-performance embedded processor, supports LCD display and embedded Linux operating system, and has the characteristics of low power consumption and easy portability.
(Note: MSC (Mobile Switching Center) mobile switching center; BTS (Base StaTIon) base station; IWF (Inter-Working FuncTIon) interworking function.)
3 The structure of the embedded wireless communication terminal system
The embedded system generally includes two parts: hardware and software. The embedded wireless communication terminal system hardware is composed of Intel XSCALE PXA 255 ARM architecture embedded processor (400MHz frequency), CDMA 1X wireless communication module YCIG-CCMG1X800, SDRAM (64Mbyte). ), FLASH (32Mbyte), 6.4-inch TFT LCD screen (true color, resolution 640x480), touch screen (four-wire resistive), power module and expansion interface (GPIO), communication terminal system hardware structure shown in Figure 2. .
3.1 Embedded microprocessor
The core of the embedded system is the embedded microprocessor. The embedded microprocessor generally has the following features: strong support for real-time multitasking, multitasking and short interrupt response time; embedded microprocessor function Low consumption, especially for portable wireless and mobile computing and communication devices. XSCALE PXA 255 is a high-performance (400MHz) low-power ARM architecture embedded microprocessor. Its main features are as follows: 7/8-stage pipeline; support for multimedia processing technology; instruction cache (I-Cache32KB) ); data fast memory (D-Cache32KB), reconfigurable to 28KB on-chip RAM; instruction memory management unit I-MMU; dynamic power management function. At present, we have selected Intel XSCALE PXA 255 according to the requirements of the system working environment.
3.2 Wireless Communication Module
The wireless communication module is the basis for establishing a wireless communication link and accessing the CDMA 1X wireless network. The CDMA 1X wireless communication module we selected is the YCIG-CCMG1X800.
The YCIG-CCMG1X800 is one of the CDMA 1X RTT (Radio Transmission Technology) wireless communication modules and can be applied to a variety of wireless terminal devices. Support R-UIM card, module allows application software development, support open AT command set. It is connected to the processor via a standard RS-232 interface. The module can directly read UIM card information, with MODEM status indicator, based on the above characteristics, we choose to use as a wireless communication module.
3.3 Memory
To meet the needs of data storage, we use 64M SDRAM and 32M Flash. The PXA 255 processor can interface with 16-bit or 32-bit asynchronous SRAM. We can access the flash memory with an interface similar to SRAM.
3.4 Display unit
The PXA255 processor integrates an LCD controller that provides an interface from the processor to the AcTIve (TFT) display. The LCD controller transfers the data in the Frame Buffer to the inside of the LCD controller and then processes it. Output data to the input pins of the LCD. The touch screen has a touch screen control chip, and the touch screen control chip is connected to the PXA 255. The touch screen is a transparent absolute positioning system, generally divided into four basic types: resistive touch screen, capacitive touch screen, infrared touch screen and acoustic surface touch screen; we design a resistive touch screen.
3.4 Power unit
The Power Supply unit adopts modular design. The input +5V output 3V and stable 5V are respectively supplied to the communication module for use and the processor. In the system design implementation, a multi-stage voltage regulator circuit and a high-precision low-power CMOS linear voltage regulator circuit are added. Power management, the power management chip is MIC5219, with overheating and overcurrent protection, working rated current can reach 150mA, suitable for our system design needs.
4 communication module hardware interface design
Serial communication is one of the most practical communication methods. On the hardware interface between the communication module and the processor, we designed a full-featured UART (Universal Receiver/Transmitter), FFUART. The UART has a Modem control pin, allowing software to pass. Control data flow, UART can perform serial/parallel conversion, the processor can read various states of UART, and FFUART supports Modem control function. The CDMA 1X wireless communication module can be functionally mapped to a wireless modem, so that the PXA 255 can easily control the communication module. The CDMA 1X communication module also has a full-featured UART, using a serial port conversion chip SP3238 between them to achieve level shifting between the two RS-232 interfaces.
5 software process design
The embedded system software design part mainly includes the operating system, drivers, and applications. The operating system we use Redhat9.0 version for custom cut, the driver is mainly serial port driver, the application program is mainly dialer. The development of these software is based on the embedded development process to establish a development environment.
5.1 Software development environment establishment
The embedded Linux development environment is generally composed of a target system hardware development board and a host platform PC with a Linux desktop version. We are using the version of Redhat 9.0 here. The target system hardware development board is used to run the embedded operating system Linux, user system applications, etc., while the host platform is used for embedded operating system kernel compilation, file system production and system application development and debugging. Both parties establish a connection relationship through a serial port, a parallel port, or an Ethernet port.
5.2 System work execution flow chart
When the system work starts, the execution flow is as shown in Figure 5.1. First, the system is powered on by the power supply provided by the power supply unit, then the bootloader is started, and then the system kernel of the embedded Linux is loaded, and then the initialization process of the peripheral module is performed. After the storage unit is ready, the initialization sequence is display unit (touch screen / TFT / LCD), GPIO (general input and output interface) and CDMA 1X wireless communication module, if the peripheral is not initialized successfully, it will be re-initialized, successful Then prepare to access the wireless network; start loading the network protocol (Point-To-Point Protocol, TCP/IP), run the user application after the successful loading, after the system is used, close the main program, and the system execution ends.
After the wireless communication terminal accesses the Internet, the application carried over the Internet can be performed. The flow of the wireless access network is shown in Figure 5.2. After the system starts, after the operating system is loaded, the CDMA 1X wireless module is initialized first, and the port terminal setting and baud rate setting are performed. The baud rate is generally set to 115200 bps; after the module is initialized, the dialing waiting state is entered because the wireless communication terminal is in The function is mapped to the wireless modem, so the login network needs to make a dial-up connection. The access number is #777, the user name and password are both cards. After the dial-up program is started, it is confirmed whether the dial-up is successful. If the dial-up is successful, the Internet service program is called, such as Web browser, user application, etc.; after the end of the Internet, close the wireless connection.
5.4 Serial Port Driver Analysis
The Linux operating system provides good support for the serial port, and embedded Linux also retains these features. When we design the serial port application, the serial port operation is mainly: setting the serial port, opening and closing the serial port, and reading and writing the serial port (receiving and sending data); the most basic setting serial port includes the baud rate setting, the check bit and the stop bit setting. In the development of driver code, you need to define some structure, use it to achieve the connection between the upper abstract operation and the underlying concrete operation. It should include serial port initialization function, open function, close function, accept function, send function; write driver code is to achieve These functions.
6 Conclusion
The system design has been applied to specific projects, and the network connection rate of 115200 bps can be achieved under the condition of good network performance. The high-performance low-power embedded processor XSCALE and CDMA 1X modules enable the wireless access system to access the Internet, enabling applications such as remote data transmission and wireless monitoring. With the continuous development of wireless communication technology and user market, wireless communication terminal access systems will have greater prospects in traffic road condition monitoring, forestry forest maintenance, industrial field data transmission, and remote image transmission.
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