Abstract: This paper designs a car GPS system based on ARM processor. It uses AT91RM9200 processor as the hardware platform, transplants the Linux operating system on the processor, and uses the operating system resources to write programs to realize GPS and GPRS functions in the car GPS. Application in the system. This paper provides a set of practical vehicle GPS positioning system design solutions with real-time monitoring capabilities.
Keywords: GPS; GPRS; ARM processor; Linux operating system
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1 Introduction
Car GPS positioning terminals have become the focus of the automotive industry in the past decade. In Europe and the United States and Japan, car GPS positioning terminals have been widely used in recent years. The vehicle GPS positioning terminal is a high-tech system integrating global satellite positioning technology (GPS) and modern wireless communication technology. The main function of the terminal is to acquire GPS data from the satellite through the GPS module, and upload the dynamic position (longitude, latitude, time, speed) of the mobile vehicle to the monitoring center through the wireless communication link in real time, and receive the information sent by the monitoring center. control commands. Most of the current vehicle monitoring systems use the GSM communication network to communicate in a short message manner, which cannot fully meet the needs of practical applications. The GPRS (General Packet Radio Service) general packet radio service is an efficient data transmission network based on the packet switching technology and adopts the IP data network protocol, which can make up for the deficiencies of the GSM network. The vehicle GPS positioning terminal not only plays a major role in the intelligent transportation system, but also provides various services such as anti-theft and anti-robbery alarms, bus reporting stations, and logistics vehicle scheduling.
2 hardware design of car GPS positioning system
This part introduces the design scheme of the hardware system of the car GPS positioning system, focusing on the design of the hardware system of the embedded processor AT91RM9200, the interface design of the GPS satellite data acquisition module and the design of the interface of the GPRS communication module. As shown in Figure 1, the hardware structure of the vehicle GPS positioning system is mainly composed of a GPRS receiving module, a GPS receiving module, an SDRAM, a FLASH memory module, a serial communication module, and peripheral modules.
Figure 1 The hardware structure of the car GPS positioning system
2.1 GPRS receiving module circuit design
The GPRS module is responsible for the communication task between the main circuit board and the monitoring center, and sends the processed GPS data to the monitoring center through the network, and receives the control command sent by the monitoring center to the main circuit board, and the module directly affects the vehicle terminal. Actual use effect.
The GPRS module selected by this system is the GR47 module introduced by Sony Ericsson. The main feature of this module is the built-in TCP/TP protocol stack. It allows a TCP/UDP transport mechanism to be used with minimal up-front configuration and operation. Its embedded controller facilitates integration of customer applications and reduces the need for external controllers. GR47 supports dual-band GSM broadband 900MHz/1800MHz, which can send or receive data through SMS short message service, CSD, HSCSD or GPRS, and can handle voice and fax. Its TCP/IP stack can also be accessed via AT commands or embedded applications. Since the GR47 module has a built-in TCP/IP protocol stack, it can be directly controlled by the AT command, which is very convenient to use. Figure 2 depicts the serial port circuit design of the GPRS communication module.
Figure 2 GPRS module serial port circuit design
2.2 GPRS module SIM card circuit design
The GR47 module has a SIM card interface that complies with the IS07816 IC card standard. It is connected to the externally extended SIM card case via a wire. Figure 3 depicts the SIM card circuit design of the GPRS module.
Figure 3 GPRS module SIM card circuit design
2.3 GPS receiver module circuit design
The GPS module is responsible for receiving the navigation message sent by the GPS positioning satellite. It is connected to the main circuit board through the serial interface, which is the key to receiving GPS data.
For the selection of GPS modules, it is usually considered from the aspects of technical parameters, supported communication protocols, control interfaces and costs. At present, commercial GPS modules mostly support 12 channels, adopt C/A coding, NMEA0183 protocol, and control through RS232 interface. The GPS satellite data acquisition module selected by this system is the GPS-R25 GPS module produced by Shanghai Lilang Company. It has the following features: 12-channel C/A code receiving control, which can simultaneously monitor 12 satellite signals; internal integrated 16-bit ARM7TDMI processing The core; the battery will be charged during normal use; the GPS satellite acquisition module has an error range of 1 to 5 meters; 2 interfaces are connected and the user can choose the baud rate; the industrial standard is achieved and waterproof. And the module can be connected to the main circuit board through the RS-232 serial port, or can be connected to the main circuit board through the PS2 interface, which is very convenient to use.
2.4 FLASH memory circuit design
Flash memory is a kind of memory that can be erased after the system is erased and the information is not lost after power-off. As a non-volatile memory, Flash is usually used in the system to store program code, constant tables, and some user data that needs to be saved after the system is powered off. The system uses a K9F5608U0A NAND flash, K9F5608U0A is one of the K9XXXXXU0A series flash memory produced by Samsung, 32MB capacity, fast read and write speed, long data retention time and up to 100,000 erase write life. The chip has an eight-bit I/O port. When CE is low, set WE low and address, command, and data can be written through this port. Data is latched on the rising edge of WE, and CLE and ALE are used to control the latching of commands and addresses, respectively. At the same time, K9F5608U0A has strong error correction function, which can protect user data to the utmost.
2.5 SDRAM memory circuit design
SDRAM access speed is much higher than Flash memory, with read/write properties, so SDRAM is mainly used as the program's running space, data and stack area in the system. When the system starts, the CPU first reads the startup code from the reset address 0x0. After the initialization of the system is completed, the program code should be transferred to the SDRAM to improve the running speed of the system. The system, the user stack, and the running data are also placed. In SDRAM. Use HY57V281620 type SDRAM in the main circuit board. The system uses two HY57V281620 to build a 32-bit SDRAM memory system in parallel. One of them is 16 bits high and the other is 16 bits low. Two HY57V281620 can be configured as a whole to any external memory area. The SDRAM memory circuit design is shown in Figure 4.
Figure 4 Connection diagram of HY57V281620
3 software design of vehicle GPS positioning system
The application program of the car GPS system can be divided into seven functional modules, namely, an initialization module, a control module, a GPS data acquisition module, an uplink data conversion module, a user interface module, a communication module and a downlink data processing module.
The initialization module mainly realizes the initialization of the serial port and zeros all the flags; the control module mainly performs the corresponding operations according to the commands of the upper computer, such as collecting GPS data, transmitting the current driving state, etc.; the main function of the user interface module is to put the GPS Data, status data, etc. are displayed on the touch screen while also responding to interruptions on the touch screen in order to implement the function of operating the vehicle terminal through the touch screen.
The main function of the GPS data acquisition module is to obtain the current GPS information through the GPS module connected to the serial port; in this program, the GPRMC positioning statement is used, and other information will be ignored. The idea of ​​extracting the GPRMC statement is to set a data buffer and put the received GPS data into this buffer. When the buffer is full, it will find in the buffer whether to accept the GPRMC positioning statement. If it is not received, Re-receive GPS data. If the GPRMC positioning statement is found, it is also determined whether the maximum number of bytes in the buffer from the buffer is greater than 62 bytes. (Because the GPRMC positioning statement required in this program contains 62 bytes)
The main function of the uplink data conversion module is to convert the received GPS data or related status information into a predetermined data format for communication with the monitoring center. The module will determine whether the data to be converted is GPS data information or related status information or both, and then select the corresponding conversion program. From the above introduction, it can be known that the received GPS data is sequentially stored in the data buffer, and what data is needed to be extracted to the corresponding position in the buffer. The data is stored in characters, so you must first convert it to shaped data when you actually use it. The function of the downlink data conversion module is opposite to the function of the uplink data conversion module. The command sent by the monitoring center is identified and sent to the vehicle terminal, and sent to the user interface module for display.
The main task of the communication module is to complete the communication between the vehicle terminal and the monitoring center. It can realize the wireless communication with the monitoring center through the GPRS network, or communicate with the laptop through the network port. If the distance between the vehicle terminal and the host computer is far away, it can be directly connected to the monitoring center through the GPRS network, and it is very convenient to connect the GPRS network to the monitoring center through the GR47 module. It is only convenient to send several AT commands to the GPRS module. However, the monitoring center must have a fixed IP that can access the Internet. When the vehicle terminal is started, the GR47 module will also be activated. This is the module will automatically connect to the GPRS network to enter the command mode. After the dial-up is successful, the GPRS network is connected, and then the wireless communication with the monitoring center can be realized by reading and writing the serial port connected to the GR47 module. Communication through the network port is relatively simple, and can be directly implemented by socket programming under Linux.
According to the definition of the functions of the above modules, the main flow chart of the software part is shown in Figure 5:
Figure 5 main program flow chart
4 Summary
The innovation of this paper is to use GPRS communication network for wireless communication instead of the traditional GSM short message communication mode, which not only saves the operating cost of the whole system, but also improves the data transmission speed and reliability. At the same time, it adopts industrial grade with The memory management function of the ARM9 chip AT91RM9200 as a processor, and the circuit design around it, the terminal has high reliability, and can adapt to the harsh environment, because the ARM9 chip with memory management function is selected, so it can be transplanted Linux operating system, the operating system comes with a very rich resources, making the application more powerful, but also increases the scalability of the software; finally, the vehicle positioning terminal combines GPS global positioning technology, GPRS wireless communication technology, ARM embedded The technology and the transplantation and programming of embedded Linux systems belong to an interdisciplinary engineering project. Since the system was put into the market for half a year, it has created economic benefits of more than 500,000 yuan.
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