1. Foreword In recent years, with the rapid development of the national economy and the increasing living standards of the people, the number of various motor vehicles has increased dramatically, and the demand for car navigation systems has also increased dramatically. This paper adopts the embedded system based on ARM9-Linux platform as the control platform of the system to improve the performance, integration and scalability of the system. The combination of GPS positioning technology and advanced GPRS wireless communication technology is used to realize vehicle electronics. Map navigation and short message alarm; through the design of the LCD module, the flexible display of various information of the vehicle is realized, which enriches the human-computer interaction interface and makes the system more intelligent. The vehicle GPS navigation system studied in this paper is an important branch of the Intelligent Transportation System (ITS), which is of great significance for solving urban traffic problems.
2. GPS Global Positioning System (1)
The GPS (Global Positioning System) system consists of three parts: the space part - the satellite constellation, the ground control part - the ground monitoring system and the user equipment part - the signal receiver. GPS Global Positioning System is a high-precision, all-weather and global radio navigation positioning and timing multi-function system established with the development of modern science and technology. It uses a satellite network of 24 artificial satellites located more than 20,000 kilometers from the Earth to continuously transmit positioning signals to the Earth. Any GPS receiver on the earth can receive the information of the GPS receiver's position (longitude, latitude, altitude), time and motion status as long as it receives any four or more satellite signals. The GPS system features high precision, all weather, high efficiency, versatility, easy operation and wide application.
3. The overall system design system mainly implements car navigation and mobile phone-based vehicle anti-theft functions. The whole system consists of two parts: one is the owner's mobile phone, and the other is the car part. The mobile phone part is just a mobile phone used to send and receive short messages. The vehicle part mainly realizes the positioning and navigation function of the vehicle volume. The vehicle part has two working modes: the first one is “driving modeâ€. In this mode, the owner can drive the car by himself, and the owner can conveniently use the human-computer interaction interface of the car navigation system to navigate; when the owner needs to leave his car Press the "Safe Mode" button to start the second working mode. After starting the mode, the system continuously uses GPS positioning technology to determine whether the current position of the vehicle has changed. If someone steals the vehicle and the position of the car changes after driving the car, the system will find that the latitude and longitude of the car position changes, the system will send a short message to the owner in real time through the GPRS network to report the current location of the car.
4. System hardware design The hardware of this system is mainly composed of two parts: main control module and expansion module. The block diagram of the expansion module mainly includes GPS module, LCD module and GPRS module system hardware is shown in Figure 1: 
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4.1 Main control module design (2)
The main control module design is the core of hardware design, which mainly includes power circuit, clock circuit, reset circuit, memory module circuit, JTAG interface circuit, serial port circuit, LCD interface, SPI interface and button circuit design. The processor of this paper adopts Samsung's S3C2410. The main control module is connected to the expansion module through serial port, SPI interface and LCD interface to form the whole hardware system.
4.2 GPS module selection
The GPS module mainly completes the reception and processing of GPS positioning information. The GARMIN GPS25-LVC receiver was chosen. The OEM interface signals for GPS25 are shown in Table 1:
4.3 GPRS module selection
The GPRS module can be used for wireless communication, including voice communication, sending and receiving short messages, and wireless Internet access. This system uses MC35, which is mainly used to complete the function of short message. Its hardware connection is shown in Figure 2:
5. Software design The hardware of the car navigation system lays a solid foundation for the realization of basic functions and extended functions. The design of the software system is to make full use of the resources provided by the hardware platform to realize the orderly operation of the business process, which is the important design of the whole system. component. The design of the software part mainly includes (3):
(1) Establish cross-compilation environment; (2) Migration of BootLoader; (3) Linux operating system including driver migration; (4) GPS positioning module programming; (5) GPRS communication module programming; (6) Display interface design This paper implements the design of the above interface based on MiniGUI;
5.1 GPS module software design
The GPS module mainly completes the collection, processing and storage of vehicle position information. Since GPS uses serial port communication, this paper realizes the reception, processing and storage of GPS data based on serial port communication. The basic idea of ​​the module software design is as follows: first receive the complete NMEA0183 statement, and then extract relevant data, such as time, latitude and longitude, speed, etc., and then send the data to display or send it, and save it for later viewing.
In this paper, the NMEA0183 statement of the GPS25-LVC serial port 1 output is selected. The format is: $GPRMC, 082 004, A, 399.3.47 2, N, 11 953.099 0 E, 000.0, 000.0 130 807 002.5, W*71, indicating that the current time is August 18, 2007 at 8:20:04 ( This is UTC time, not local time, which is about 8 hours apart. The position is 39 degrees 90.347 2 points north latitude, 119 degrees 53.099 0 minutes east longitude, and the speed is O.
5.2 Software design of GPRS wireless communication module In the software control of MC35 module, the standard V.25 ter AT command is mainly used. The relevant AT commands used in system development are shown in Table 2 (4).
The specific execution process of the AT command is as follows:
AT
OK
AT +CSCA = +8613800773500\ r
OK
AT +CMGF = 1 \ r
OK
AT +CMGS = + 861348137...\ r
> Your car is being stolen! \x1A
+CMGS: 206
OK
When the alarm function is running, after the above steps are completed, the alarm short message will be sent, and the owner's mobile phone will receive a text message with the content “Your car is being stolen!â€. Then, the MC35 module reads the current geographical location in real time in the corresponding storage area under the control of the MCU, and continuously reports it to the owner in the form of a short message to help the owner and the police to recover the vehicle.
5.3 Software Design for Interface Display (5)
The development of embedded applications is done on a host computer (such as a PC). The embedded application is debugged on the host machine, and the embedded application is compiled and linked into binary object code that can run on the target platform. Since the MiniGUI library is used, the MiniGUI library is compiled and linked into a binary object code library that can be run on the target platform. The development process ends when a MiniGUI application is deployed to the target platform and runs reliably. The positioning information interface displays information such as the location of the vehicle received through the GPS, and then expands the electronic map to display the information more intuitively. Figure 3 depicts the basis
MiniGUI software development process: 
6. Summary The author's innovations are as follows: 1) The car navigation function is designed and implemented on the ARM-Linux platform. The system has the characteristics of low cost, low power consumption, high processing performance and good stability. 2) This platform facilitates the software and hardware upgrade of the system.
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