| The rapid development of vehicle industry provides people's lives with convenient condition. making people's trip more convenient, goods circulation more unobstructed. There are more and more vehicles on the road and the transportation industry becomes flourishing as never before. But it simultaneously brings enormous pressure for vehicle management. supervision and inspection. Frequent appearance of traffic accident caused great threat to people's life and property security. Since the 1970s. the Vehicle Traveling Data Recorder was firstly used in Europe, which effectively reduces the traffic accidents, protects the people's life and property to some extent and brings remarkable social and economic benefits. National standard of "Vehicle Traveling Data Recorder" which was carried out in 2003 prescribes that passenger cars and trucks and some other cars should be gradually installed, use the line with the national standard vehicle traveling data recorder.Vehicle Traveling Data Recorder can record vehicles and drivers state information such as vehicle speed and mileage in traveling, drivers information, fatigue driving period and so on, can store these state information chronically and output the record information by the interface of GPRS or UART. Moreover, it reminds the driver whether he is driving in fatigue, and provides accurate effective field data for the traffic accident appraisal.With the increase of vehicles, Vehicle Traveling Data Recorder should have more functions. The traditional non-intelligent Vehicle Traveling Data Recorder cannot meet the needs of the market any longer. The Vehicle Traveling Data Recorder in this abstract adopts Atmel SAM9260 ARM9 as CPU. It is an industrial-grade processor with abundant external interfaces, excellent expansibility and stable operation. Adopted embedded Linux OS as software platform, it supports multiple processor architectures as well as a wide range of hardware device drivers. And because of the open-source it can reduce production costs.Vehicle Traveling Data Recorder needs to record vehicle information instantly and accurately. The task in our abstract used FRAM and SD card as external storage device. FRAM records the driving questionable data and driver fatigue information and SD card records configuration file and vehicle status data. These data require high real-time. Every 200ms we should write driving questionable data to FRAM. and the error should not exceed 10ms:should write fatigue information to FRAM when the driver is tired. It needs to read data from the FRAM when the server requests driving questionable data or driver fatigue information. When the system needs to modify the configuration file, it needs to rewrite the configuration file to SD card. Vehicle status data should record per minute, and the error should not exceed 5s.The advantage of FRAM is that it supports real-time storage and it has the characteristics of both ROM and RAM. Volatile memory such as SRAM and DRAM will lose data if there's no power. When vehicle is encountered some special circumstances in the process may lead to power-down. However, FRAM has the ability to save data for 45 years without power. Non-volatile memory such as EEPROM and FLASH can retain data after power failure, but these storage devices have common disadvantages that writing slowly, limited times to write, requiring large power consumption to write and so on. With a high speed to read and write. FRAM can operate like RAM. It has more than one billion times to read or write, which can be regarded as unlimited times. SD card has a series of advantages. It has a large storage space, and strong expansion. With a uniform read-write protocol, it can replace the equipment easier. The slot is firm so it won't easily fall off in case of bad road conditions and it has a high speed of transmission.In conclusion, the writer designed embedded Linux standard driven architecture and low-level FRAM device driver which was combined with FRAM pretreatment, R/W and control mechanism after a detailed study of embedded Linux operating system on driver design as well as working principles and hardware characteristics of FRAM and SD card. The writer achieved the registration, R/W and other functions of FRAM device;designed SD card low-level R/W, initialization and device registration functions based on the SD card R/W protocol.Based on the FRAM and SD card device driver, the writer designed information data storage format according to hardware characteristics of FRAM & SD card and the systemetic functional and real-time requirements. Aiming at R/W of FRAM and SD card device nodes based on embedded Linux and its application features, the writer completed application functions to read and write data.Finally, by FRAM and SD card functionality test show that the device driver can identify equipment, and can successfully register FRAM and SD card. The driver is stable. R/W module of FRAM and SD card works well with high real-time, and meets the "Vehicle Traveling Data Recorder" national standard. |
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