Design of automotive "black box" based on ARM

0 Preface

The car driving recorder, commonly known as the car black box, is an electronic device that can record the vehicle's driving speed, time, mileage and other status information. The driving recorder can record the relevant information of the vehicle operation and the driver's driving activities in real time. By checking, monitoring, feedback and interactively managing the relevant information such as the vehicle's driving speed, continuous driving time, mileage and other operating status, it can effectively realize the driver's driving time, driving speed, driving route, etc. All-round constraints and control, curb serious traffic violations such as fatigue driving and vehicle speeding, prevent road traffic accidents, and standardize vehicle management. Statistics show that the use of car black boxes has reduced the traffic accident rate by 37%~52%, greatly reduced casualties and property losses, and produced significant social and economic benefits. In October 2003, the Ministry of Public Security Traffic Safety Product Quality Supervision and Inspection Center issued the national standard GB1 T1905622003 for car driving recorders. The car "black box" will undoubtedly become a new specification. With the continuous increase in vehicles and the continuous congestion of traffic, in order to ensure traffic safety, the mandatory installation of driving recorders will be implemented in the future.

1 Classification of "black boxes"

Due to the different starting points of each manufacturer, the types of products are different and the product structures are also different. At present, the recorders on the market have formed a product pattern with various types and different performances. According to their different functions, car driving recorders can be divided into single type, accident type, management type, comprehensive management type and 3G type.

The 3G model is a new generation of vehicle driving recorder developed with comprehensive management as the main purpose, which has been optimized in terms of software, hardware and system functions. Its main features are multi-channel data acquisition and processing, continuous recording throughout the process, large-capacity storage card and powerful comprehensive management software system to achieve resource sharing. This type of recorder uses powerful modern technical means such as multi-channel data acquisition and processing platform, GPS satellite positioning device, large-capacity data storage card, increasingly mature geographic information system and background comprehensive management platform software, focusing on the comprehensive management goals of operating and special vehicles to complete the process of comprehensive vehicle management. Through the continuous recording curve of the whole process and the continuous state of each switch sensor replayed on the microcomputer software interface, the comprehensive indicators such as vehicle operation, safety and quality can be strongly monitored throughout the process, and statistical charts can be printed according to needs, and dynamic analysis methods can be adopted to provide extremely valuable reference for the driver's safe driving.

2 Overall system design

This system consists of a vehicle-mounted host and monitoring software. The host uses TI's 32-bit RISC microprocessor TMS470R1A256 as the main controller, including basic recording module, display module, printer module, GPS module, GPRS module, and data communication module. The overall design block diagram of the system is shown in Figure 1.

Figure 1 System block diagram

The system collects three signals, namely external analog signal input, digital signal input and switch input, through TMS470R1A256. The data to be saved is stored in the internal large-capacity memory after processing. Real-time data (such as real-time vehicle speed, real-time time) and alarm signals can be output and displayed through the display panel. The GPS module measures the latitude and longitude, speed, and realizes remote monitoring and real-time tracking through GPRS.

3 System Hardware Design

3. 1 TMS470R1A256.

The TMS470R1A256 is a series product of TI TMS470R1x general-purpose 16/32-bit reduced instruction set (RISC) microcontroller.

The TMS470R1A256 mainly includes the following resources: 256 KBFlash, 12 KBSRAM, zero-pin phase-locked loop (ZPLL) clock module, analog watchdog (AWD) timer, real-time interrupt (RTI), serial peripheral interface (SPI), serial communication interface (SCIx), standard CAN controller (SCC), type II serial interface (C2Sib), external clock divider (ECP), 10-bit multi-buffered ADC (MibADC), 16 input channels, high-end timer (HET), up to 49 I/O ports and one input-only port.

The Flash memory of TMS470R1A256 is a non-volatile, electrically erasable, programmable memory with a 32-bit wide data bus interface. Flash operations are performed at the system clock frequency, which can reach 24MHz. In pipeline mode, the frequency can reach 48 MHz.

SCI is a full-duplex, serial I/O interface that implements asynchronous communication between the CPU and peripheral devices using the standard non-return-to-zero (NRZ) format. SCC uses a serial, multi-host communication protocol to achieve efficient distributed real-time control and stable communication up to 1Mbit/s. SCC is ideal for applications requiring reliable serial and multi-channel communication in high noise and harsh environments. C2Sib enables the TMS470R1A256 to send and receive information on a Class II network that follows the SAEJ I850 protocol standard.

3.2 Communication between TMS470R1A256 and MC33993

The programmable multi-way switch detection interface integrated circuit MC33993 launched by MOTOROLA in the United States can detect up to 22 switch input signals, and can transmit the detected multi-way switch status (three-state) signal to the MCU through the SPI port of the chip. In addition, the device also has a 22-way analog multi-way switch function, which can be used to read multiple analog input signals. The analog input signal can be output by the analog multi-way switch through the buffer for MCU to read. And MC33993 can make the entire system including MCU work at a lower quiescent current, which is very important for systems such as remote monitoring, because for them, current consumption is an important design consideration. Therefore, this design uses MC33993 as the multi-way switch detection interface circuit.

In the system, MC33993 uses SPI to realize hardware connection with MCU, as shown in Figure 2: When there is external switch input and the state changes, MC33993 will send an interrupt signal IN T to TMS470R1A256, and TMS470R1A256 responds to the interrupt to read the switch input state, thereby improving the working efficiency of MCU.

Figure 2 Hardware connection between MC33993 and TMS470R1A256

3.3 Communication between TMS470R1A256 and FM24L256

In the automotive driving recorder industry, data security is the most important thing. With the development of recorders, the amount of data stored is getting larger and larger, which requires large-capacity memory, but the large-capacity EEPROM index is not very high, especially the number of erase and write times and speed affect the quality of the energy meter itself. FM24L256 is a new type of memory developed by RAMTRON. Its core technology is ferroelectric crystal material, which has the characteristics of random access memory and non-volatile storage products. FM24L256 and AT24C256 have the same capacity and compatible bus structure, but the performance index of FM24L256 is much greater than that of AT24C256.

The communication mode of FM24L256 is a two-way two-wire protocol, which has few pins and occupies little space on the circuit board. Figure 3 describes the hardware connection mode of FM24L256 and MCU.

Figure 3 Hardware connection between FM24L256 and TMS470RIA256

3.4 Communication between TMS470R1A256 and SL811HS

The USB host in this system transmits data with the USB device through the host controller. The USB host should have the following functions: detect the plugging and unplugging of USB devices; manage the control flow between the USB host and the USB device; manage the data flow between the USB host and the device and collect the status of the USB host.

SL811HS is a USB control chip produced by CYPRESS that supports full-speed data transmission. It also contains a USB master-slave controller, supports full-speed and low-speed data transmission, and can automatically identify low-speed or full-speed devices. The interface provided by SL811HS complies with the USB1.1 standard and can be connected to the TMS470R1A256 microprocessor. The data interface of SL811HS can provide 8-bit data I/O or bidirectional DMA channels when interfacing with the microprocessor, and can support DMA data transmission in slave operation mode. SL811HS has a 256-byte RAM inside, which can be used as a control register or data buffer. The hardware connection method of SL811HS and TMS470R1A256 is shown in Figure 4.

Figure 4 Hardware connection between SL811HS and TMS470R1A256

3.5 Communication between TMS470R1A256 and HOLUXGR285

HOLUXGR285 intelligent satellite receiving module adopts the second generation satellite positioning receiving chip designed by the American company SURF. It is a complete satellite positioning receiver. It has all-round functions and can meet the strict requirements of professional positioning and personal consumption needs. The scope of application ranges from car navigation, security systems, map making, etc.

HOLUXGR285 communicates with other electronic devices via RS2232 and TTL, and stores satellite data with a built-in rechargeable battery.

It consumes low power and can track signals from 12 positioning satellites simultaneously, receiving signals every 0.1 seconds and updating positioning information once a second.

HOLUXGR285 and TMS470R1A256 are both 3.

3V power supply, so data exchange can be achieved through the serial communication port without level conversion. The hardware connection is shown in Figure 5.