Electronic Traffic Police System Based on Embedded Web

    In recent years, the intelligent transportation system has developed rapidly. It strives to effectively integrate advanced information technology, communication technology, computer technology, electronic control technology and other high-tech technologies into the entire transportation management system, and establish a comprehensive, real-time, accurate and high-quality integrated transportation management system on a large scale. So far, countries and regions such as Japan, the United States, Western Europe, and Australia have established corresponding institutions to engage in related development and application research, and have achieved some results.

    Running a red light is one of the main causes of traffic accidents. The main function of this electronic traffic police system is to capture and process the phenomenon of motor vehicles running red lights, which is an important part of the modern urban traffic monitoring system. At present, since the relevant information of motor vehicles running red lights has not been connected to the network in real time, there is a great lag in the later management of the acceptance, fines, and settlement of illegal vehicles. Therefore, this system adopts an embedded Web-based solution to ensure the real-time performance of the system, and the use of high-precision digital cameras makes up for the lack of clarity of CCD cameras. A good application effect has been achieved.

1 Design scheme
    Figure 1 is the overall design scheme of the system.

1.1 Hardware Part
    The structure of the hardware part is shown in Figure 2.

    ARM (Adranted RISC Machines) is a world-renowned company in the microprocessor industry. It has designed a large number of high-performance, low-energy, and low-cost RISC processors and related software. From the perspective of cost-effectiveness and practicality, this system uses Samsung's embedded processor S3C4510B based on the ARM7 core. The development board system built with external memory chips, main USB interface, Ethernet chip, serial and parallel ports is used as the hardware development platform of the entire system. According to actual needs, different parameters are set in the interface logic circuit, and appropriate base addresses and interrupt numbers are set to avoid conflicts. At the same time, pins are allocated according to the instructions of the development board.

1.2 Embedded system software structure
    This system uses the μCLinux operating system.

    At present, the embedded operating systems with open source codes are μC/OS and μCLinux, and they each have their own characteristics. μC/OS occupies less space and has excellent real-time performance. Although μCLinux occupies a relatively large space and has average real-time performance, it has the ability to support multiple file systems, has an embedded TCP/IP protocol, can draw on the rich resources of Linux, and is suitable for more complex systems. Since this system needs to be Ethernet-oriented and is relatively complex, μCLinux is selected as the operating system. μCLinux is a variant of Linux. The main difference between the two is the memory management mechanism and process scheduling management mechanism. At the same time, in order to meet the needs of embedded applications, μCLinux uses the romfs file system and simplifies the C language library glibc on Linux.

    The software design of this system includes: platform porting of the μCLinux operating system, tailoring of the embedded operating system μCLinux, hardware drivers, applications, human-machine interface, etc.

    (1) Port μCLinux on the ARM platform and establish the μCLinux development environment on the PC. The ARM development board is used to run the operating system and application software, while the PC completes the kernel compilation of the operating system used by the target board and the development and debugging of the application. The connection between the two is generally established through the serial port, parallel port or Ethernet interface.
    (2) The system kernel is tailored to minimize the resources occupied while ensuring the function.
    (3) The hardware driver includes USB driver, USB controller driver, Ethernet controller driver, etc.
    (4) The application is mainly responsible for transmitting the data uploaded by USB and serial port to Ethernet.
    (5) The human-machine interface includes local interface and remote interface. The remote interface is mainly stored in the dynamic web page in the embedded server for management and query. [page]

2 System composition
    This system consists of the front-end vehicle camera control subsystem, information transmission subsystem and information query management subsystem. The composition structure is shown in Figure 3.

2.1 Vehicle Photo Control Subsystem
    The front-end vehicle photo control system consists of an embedded system, a microcomputer chip ground sensor coil detection device, a high-precision digital camera, and related communication and transmission accessories. At the moment when the illegal vehicle hears the red light, the microcomputer chip sends out the vehicle violation signal in a timely and accurate manner according to the signal change of the ground sensor coil. After receiving the detection signal (running a red light, driving in the wrong direction, etc.), the front-end embedded control host controls the shutter of the digital camera and determines whether to turn on the flash at any time based on the brightness of the surrounding environment. The digital camera takes pictures after receiving the flash and photo signal. The captured information is first stored in the camera's 8M card (Smart Media Card).

2.2 Information Transmission Subsystem
    Information is transmitted through the network. At present, there are roughly three ways for embedded systems to access Intcnlet: one is through a dedicated Web server; the second is through a dedicated embedded gateway; the third is to extend the standard network technology (TCP/IP) to embedded devices, and the embedded system itself implements the Web server function. This article adopts the third method, which only requires writing dynamic web pages to conveniently manage and query related information through a Web browser.

    The information transmission subsystem consists of two parts: one is the transmission process of photos and other related information from the digital camera USB port to the Ethernet controller; the other is the transmission process of information from the Ethernet controller to the Ethernet.

2.2.1 Information transmission from the digital camera to the Ethernet controller
    After the green light at the intersection is on, the photo processing task in the embedded system determines whether there are photos stored in the camera. If so, the photos are transferred to the Ethernet controller through the USB interface of the digital camera to ensure that the digital camera has enough space to take photos of violations at any time. At the same time, the violation time, location, and violation scene data are saved in the photos to facilitate the subsequent processing of the photos.

    The digital camera and the Ethernet controller transmit information through the main USB port. The main USB chip used in this system is the SL811HS of Cypress. This chip is specially developed for embedded systems, is low-priced, and complies with the USBl.1 specification.

2.2.2 Information transmission from the Ethernet controller to the Ethernet
    The Ethernet controller is connected to the Ethernet, and the photos of violations taken are transmitted to the Ethernet in real time, and finally the real-time transmission of related information such as violation photos is realized.

2.3 Information management query subsystem based on B/S structure
    The violation photos of vehicles are the basis for the traffic control department to deal with the violating drivers, so the photos sent back by the front end also need to be managed. The monitoring center establishes a computer local area network system and sets up multiple workstations to input, review, accept, deliver, inform, block files, re-examination notice, fine, unblock files, and complete the work of photos.

    The system must be interconnected with basic databases such as motor vehicles and drivers to conduct strict search, comparison, transfer, and file sealing. It must also be interconnected with multiple external systems to inform traffic violations and track the execution of fines. The external systems involved mainly include the post office delivery system, bank collection system, motor vehicle and driver query database, and traffic violation database.

3 Key issues in the design
3.1 Realization of Ethernet access based on embedded Web
    The system uses S3C4510B embedded processor and Ethernet interface chip RTL8201BL to form an Ethernet measurement and control gateway. RTL8201BL is connected to S3C4510B processor through bus, and interruption is also taken over by external interruption of S3C4510B.

    The network layer mainly completes the conversion between Ethernet TCP/IP protocol and illegal fieldbus RS-232 and other protocols, completes the interconnection between Ethernet and fieldbus network, and realizes data exchange between different Ethernet and fieldbus networks.

    Data flow: Request information comes from Ethernet, through RJ45 interface to RTL820BL, IP packet is sent to S3C4510B, unpacked, data is taken out, and then re-framed according to RS-232 and other fieldbus communication protocols; or the data frame sent by the front-end camera system is re-packed into IP packet and sent to Ethernet.

    The key to network transmission is to develop TCP/IP protocol stack responsible for data transmission and remote command processing. First, select the type of network protocol. Since the amount of data that needs to be transmitted is not large, but the reliability requirement is high, the reliable data transmission control protocol TCP is selected in the transport layer, and the basic data transmission protocol IP is selected in the network layer.

3.2 Writing hardware drivers in the embedded system μClinux
    Hardware drivers include USB drivers, USB controller drivers, Ethernet controller drivers, etc. In Linux, drivers can be compiled in two ways, one is static compilation into the kernel, and the other is compilation into modules for dynamic loading. Since μCLinux does not support dynamic module loading, the method of static compilation of device drivers into the μCLinux kernel is selected here. When the Linux kernel starts, the initialization function of the device driver will be called to initialize the device. A major device number and a slave device number need to be assigned to the device, which cannot be repeated with the existing device number, and then a new device file is created. Add the device driver file in the corresponding directory, modify the corresponding Config.ini and Makefde files, load the corresponding device driver when the kernel is compiled, and burn the generated μCLinux binary file into the flash memory. Then, various external devices can be used. The interrupt processing in the driver adopts the processing method of the upper half and the lower half. The upper half completes the interrupt registration, the calibration of the interrupt cause, the scheduling of the lower half, and then exits. The lower part performs data processing when it is relatively safe, so that the upper part can continue to serve other interrupts while the lower part is working.

    The electronic traffic police system uses high-tech means such as embedded Web and digital communication to transmit the information of illegal vehicles to Ethernet in real time. The monitoring center can easily manage the information, and users can query it at any time through the Web browser. Nowadays, digital camera technology is changing with each passing day. The shutter speed of general digital cameras can reach 1/1 000s, and multiple continuous shooting is supported, which can fully meet the requirements of high precision and three elements. The use of embedded Web enhances the real-time and reliability of the system, greatly reducing the delay time of a series of processes such as violations, payment and database updates. It replaces PCs with microcontrollers and Ethernet interface chips for on-site control, and only requires a few network computers for monitoring, which greatly reduces costs. Using the rich resources of digital cameras and Ethernet to build this control system is a real-time, low-cost and highly reliable technical solution. The establishment of this system effectively improves the efficiency of recording and post-management of vehicles running red lights, improves the level of traffic management, and has good economic benefits and broad application prospects.

References:

[1]. RISC datasheet http://www.dzsc.com/datasheet/RISC_1189725.html.
[2]. SL811HS datasheet http://www.dzsc.com/datasheet/SL811HS_611618.html.
[3]. RTL8201BL datasheet http://www.dzsc.com/datasheet/RTL8201BL_html.
[4]. RS-232 datasheet http://www.dzsc.com/datasheet/RS-232_584855.html.