Vehicle navigation is a topic that combines technologies in the fields of automobiles, computers, communications, transportation, and systems science. It has always been the focus of research by many high-tech companies and universities at home and abroad.
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In contrast, the development of domestic navigation systems is relatively slow, and there is a big gap between foreign manufacturers in terms of hardware manufacturing, software functions, electronic maps, etc. So far, there are very few high-quality navigation products that are practical and practical; The level of software and hardware is advanced, but it is not restricted by factors such as the electronic map database, nor has it entered the domestic market on a large scale.
In recent years, the embedded system has developed rapidly and leaps forward with its powerful functions, compact size, and extremely low power consumption. It has gradually penetrated into all aspects of life and brought new impetus to the development of vehicle navigation systems.
This paper introduces a design scheme of embedded vehicle navigation system. It adopts ETX (Embedded Technology Extended) hardware platform and VxWorks embedded operating system based on X86 architecture. It can better meet the requirements of navigation system in hardware and software, and has good performance. Application prospects.
1. The composition of the vehicle navigation system
A brief introduction to each section is as follows:
Path guidance: guide the user along the planned path;
Man-machine interface: Provides a friendly interface that allows users to interact with the system;
Wireless communication module: allows users to exchange information with the monitoring center and other departments in real time;
Electronic map database: contains digital map information stored in a predetermined format, which is a software platform of the system;
Map matching module: determining the location of the vehicle on the map through an appropriate matching and identification process;
Path planning: help drivers plan routes based on map database and real-time location information;
Positioning module: Position the vehicle by means of GPS, inertial navigation system or mobile communication.
Combined with the actual hardware and software structure, the system is divided into four layers: the bottom layer is the hardware platform layer, which contains the ETX embedded CPU module and the necessary sensors/submodules.
The above three layers are software layers, in which the device driver layer acts as a bridge between the hardware platform and the operating system, providing a unified interface independent of hardware devices for the upper layer; the VxWorks system layer provides library functions, application programs, and tasks. The scheduling mechanism provides support for the user program; the application software layer is a program developed by the user, and mainly includes an electronic map and a navigation application, and is also a core part of the system. The following describes the system from both hardware and software.
2, the hardware structure of the system
(1) CPU module
The requirements of the vehicle navigation system for the hardware platform are: miniaturization, low power consumption, rich interfaces, and can adapt to complex environments. The ETX embedded CPU module selected by this system can fully meet these requirements. It uses an Intel Pentium III processor and uses ACPI. APM1.2 power management reduces power consumption, eliminating the need for a fan unit to dissipate heat.
In addition, it uses VIAVT8603/VT82C686A chipset, S3Savage4 graphics card and VIA-enhanced sound card, with 2 EIDE interfaces, supports UltraDMA/33, and 4 USB1.1, 2 serial ports, 1 EPP parallel port and so on.
ETX also provides an ISA bus interface and a PCI bus interface, and has a watchdog that can effectively solve the crash problem. The 4Ã—100pin bus on the back side defines various standard interface signals. It can be used only in the corresponding socket of the motherboard design. It is very convenient to develop.
(2) Serial port expansion module
Considering that the system requires multiple serial ports (communication with the host computer, receiving GPS information, sending and receiving short messages, communicating with the voice module, etc.), the ETX module only has two serial ports, so the TL16C554 is used for serial port expansion.
It has a 16-byte transceiver FIFO universal asynchronous transceiver with independent transceiver control circuit to control 4 standard serial interfaces. The software can set the interrupt permission, baud rate and data frame format of each channel. .
The TL16C554 is connected to the ISA bus of the ETX, and the timing of the two is converted by a CPLD. Because the system's interrupt resources are relatively tight, and considering that the data of each sub-module is not very frequent, four extended serial port shared interrupt schemes are adopted.
(3) Path guidance module
The system uses the voice mode to guide the path, and adopts the XF-S3111 Chinese speech synthesis chip produced by Anhui Keda Xunfei Company. It is a Chinese speech synthesis chip designed by InterSound3.0 Chinese speech synthesis system, which is the latest research result in the field of embedded Chinese speech synthesis. It receives the text to be synthesized through the asynchronous serial port and directly synthesizes it into speech output, which is small in size. Easy to use, it is a complete and inexpensive voice solution.
(4) Wireless communication module
The wireless communication part of the system adopts the short message mode, and the short message module DTR2000 produced by Shenzhen Kelingtong Technology Co., Ltd. is selected. It is mainly composed of an industrial grade GSM module produced by Siemens and a high-performance processor. It can realize wireless data transmission through short message function and supports Chinese transmission. The transmission data is transparent, the protocol is simple, and the communication between modules and between the module and the mobile phone can be conveniently performed.
The system adopts the GPS positioning mode, displays the electronic map and the positioning point through the color LCD, and adopts the CF card directly connected with the ETX as the storage device.
3, the system software design
Because the vehicle navigation system has higher requirements for multi-tasking, real-time and stability, the system uses the VxWorks embedded operating system. It includes process management, storage management, device management, file system management, network protocol and system application. It is highly scalable and takes up very little storage space, ensuring that it can run at higher efficiency. In the navigation system.
VxWorks includes core features such as microkernel wind, advanced network support, powerful file system and I/O management, C and other standard support. The microkernel wind is at the core of the VxWorks operating system and supports all real-time features: fast task switching, interrupt support, preemptive and time slice rotation scheduling, etc., which can meet the real-time and multi-tasking requirements of the navigation system.
The software functions of this system are divided into two parts: driver and application software in VxWorks environment. The former is mainly for the development of the TL16C554 driver, while other devices (such as graphics cards, network cards, etc.) do not need to be involved because VxWorks comes with X86 related drivers. The driver development of TL16C554 can be referred to VxWorks' own serial driver template. Here is a brief description of the development steps.
The serial device driver of the VxWorks system is not directly attached to the IO system, but is instead served as a translation layer by the virtual device ttyDrv. Therefore, the driver needs to be driven according to the system interface and hang on ttyDrv.
First, you need to modify the relevant parameters in the config.h, sysSerial.c and other files, and then write the specific driver to implement the device's I / O operations, including the TL16C554 initialization function, I / O control functions, interrupt handling functions.
In this way, the system will install the device and driver at initialization time, and the application can perform I/O operations in a unified manner independent of the device.
Application development includes electronic map and navigation application design:
(1) Design of electronic map
The design of the electronic map includes two parts: a graphical interface and a map database. The system realizes the graphical interface of the electronic map through VxWorks' WindML (WindRiverMultimediaLibrary).
WindML is primarily used to implement basic graphics, video and audio technologies and to design standard device driver frameworks that provide a unified graphical hardware interface and the ability to handle input device and input device events. The data structure of the electronic map database uses the Arc-Node structure.
The basic principle of the structure is to adopt the idea of â€‹â€‹â€œsingle generationâ€, that is, by adding a plurality of nodes to simulate or approximate the real road in reality by a series of line segments within the allowable precision range, the entire road network is composed of Arc (small segment) and Node (Arc's two endpoints) are composed of a clear topological relationship for path planning. The system realizes the electronic map within the fourth ring of Beijing, and realizes functions such as map browsing, location query and path planning.
(2) Design of navigation application
The navigation application includes functions such as operation of an electronic map, GPS positioning, sending and receiving short messages, voice prompts, and human-machine interfaces. In the design, according to the good multi-tasking features provided by VxWorks, different navigation function modules are assigned to different tasks for execution, and multi-task synchronization is ensured through the inter-task communication mechanism. The main task of the system is responsible for the initialization of hardware devices (such as serial port, watchdog configuration, etc.), initialization and first display of electronic maps, and initiation of subtasks.
Four subtasks are initiated in the main task, which are responsible for responding to user input, data input of standard serial port, data input of ISA bus 16C554, and implementing path planning algorithm.
The first three functions are independent because the trigger times for these functions are undefined and need to be monitored separately; the last one is because of the large amount of computation required. Here, only the subtask that receives the serial port data is taken as an example for analysis.
This task requires monitoring the information of the two serial ports: GPS data and status information returned from the voice module. VxWorks designs the I/O system as a device-independent interface, so the operation of the serial port can be considered as an operation on the file.
The serial port is easy to open, close and write, and the serial port read operation uses the select function to block the task with its trigger mechanism. When data arrives, the task will be activated and read data from the serial port. Then, through the inter-task communication mechanism, the main task will be notified to perform corresponding processing, such as performing map update and outputting voice prompts.
After the experiment, the system can run stably and reliably. The system demonstrates its GPS positioning and path planning capabilities. The implementation of the system's functions proves the excellent performance of the ETX platform and the VxWorks operating system, indicating that the combination of the two has the advantages of simple development, reliable performance, etc., and has a good application prospect.
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