基于V4L2嵌入式图像采集的实现毕业论文外文翻译

1、外文原文The Implementation of Embedded Image Acquisition Based on V4L2 LU Yinli,YU Hongli,ZHANG Pengpeng Physical Electronics,Department of Electrical Engineering of University of South China Hengyang,Peoples Republic of China luyinli198755,tianqing924 AbstractIn view of the current situation of the les

2、s embedded Linux image acquisition application based on V4L2(Video for Linux Two), embedded image acquisition system based on V4L2 is designed.S3C6410 is adopted as hardware development platform and Linux as software platform. After loading the driver of CMOS camera OV9650 and other relative drivers

3、, image acquisition applications on the basis of V4L2 is compiled, adopting double frame buffer to reduce CPU utilization rate to accomplish acquisition and preview image. With the size of 400480 and the frame rate of 15 frames per second, the picture collected shows clearly and it has good quality.

4、 The experiment result indicates that the system has good scalability, and it offers a new idea for embedded hand-held devices. Keywords-V4L2; OV9650; image acquisition; S3C6410; double frame buffer INTRODUCTION The video image processing technology is widely used in electronic technology and comput

5、er technology. The image from a camera or other image acquisition equipments is transformed mathematically to get the information of digital image; then, it is encoded, filtered, enhanced, recovered, compressed, stored and other processes conducted by the computer; visual images and other results fi

6、nally will be received. With the development of embedded technology, the current image acquisition technology is transformed from the analogue to the digital. Among them, embedded image acquisition attracts more and more peoples attention for its superior performance.Embedded microprocessor is the b

7、est choice for the image processing system because of its high performance, cost-effective, and low power. Samsung S3C6410 has ARM11 core and adopts 64/32 bit internal bus architecture. It also includes many powerful hardware accelerators such as motion video processing, audio process and so on. An

8、integrated MFC (Multi Format codec) supports encoding and decoding of MPEG4/ H.263/H.264 and decoding of VC1,so it is very convenient for image processing .S3C6410 is utilized as the core of the embedded hardware platform, the paper designs a image collection applications on base of V4L2.After addin

9、g support for OV9650 and V4L2 to the kernel and transplanting Linux operating system to the hardware platform, image acquisition applications, using double frame buffer to reduce power consumption, is devised on the basis of V4L2, ultimately, picture will be gathered and showed on the LCD. II. HARDW

10、ARE SYSTEM STRUCTURE The whole image acquisition system mainly includes CMOS camera OV9650, core controller S3C6410, LCD and others peripherals. The system hardware structure is showed as figure 1: A. Processor: Samsung S3C6410 is based on ARM1176JZF-S core, and its main frequency is 533MHz/667MHz,

11、including SIMD( single instruction multiple data) for media processing. It applies special ways to make it suitable for video processing. B. Camera: OmniVisions OV9650 is used here. It incorporates a 10 bit A/D converter, corresponding to data output interface D0:9. The output image data format can

12、be 10 bit raw RGB or 8 bit RGB/ YCbCr through internal DSP processing. The CAMIF used supports ITU-BT 601/656 YCbCr 8 bit mode. As a result, D9:2of OV9650 should be connected to the data interface of CAMIF for S3C6410. C. Peripherals: This part mainly includes LCD and touch screen interface circuit,

13、 JTAG debugging circuit, reset circuit, the power supply circuit, RS232 serial interface circuit and so on. Because OV9650 registers control protocol SCCB(serial camera control bus) can be compatible with I2C,so we use I2C of back-end platform to simulate SCCB to configure the OV9650 internal regist

14、ers. III. SOFTWARE DESIGN There are two steps to achieve the realization of image collection: firstly, load the relating driver to Linux kernel on the bottom; secondly, compile image acquisition applications on the top to get image data, which will be showed on LCD finally.A. Load the relating Drive

15、r Before compiling the applications procedure, drivers related should be loaded at first. Because the kernel adopted includes the drivers, so just add correlative configuration to the kernel. 1) kernel configuration: In the directory of kernel, use the command make menuconfig for kernel configuratio

16、n: choose Device Drivers Multimedia device Video for linux, load video4linux module to provide programming interface for video device; choose Device Drivers Multimedia devices Video capture adapters Samsung Camera Interface drivers External Camera OVT OV965x,add the support of CMOS image sensor to t

17、he kernel. Save the configuration and quit. 2) generate kernel image Use the commands below: make dep: read the configuration file and creat dependency tree corresponding to the configuration to determine compile options; make zImage: generate the kernel image that can support V4L2 and OV9650. When

18、the kernel starts, if there is the same information as follows, it indicates that the driver of OV9650 has been loaded successfully: CAM OV9650 init reg start. CAM OV9650 init reg end. After the system starts, it can automatically identify OV9650 ,System calls can be utilized to obtain equipment inf

19、ormation to facilitate application development, the I/O operation interface function provided by CMOS image sensor driver can realize the relevant operation. B. Image Acquisition Applications V4L is a range of interface functions provided by Linux for video devices applications, the image data can b

20、e read out from video equipment by using API functions. 1) V4L2 driver structure V4L has two shortages:when driving program is being designed, you cannot open multiple equipment at the same time;furthermore,V4L API cannot well support equipments with encoding ability. Under this circumstance, Bill D

21、irks redesigned a set of APIs and data structure, called V4L2.Compared to V4L,the extensibility and flexibility are improved, more video devices are included in its management. Although V4L2 is the updated version of V4L, they are not compatible.V4L2 is applied as Linux2.6 kernel driver agreement. A

22、s a specifications of video capture device driver for Linux, V4L2 adopts a layered approach to offer clear and consistent interface for driver development: the application is at the top, V4L2 in the middle layer, while he actual hardware device on the bottom. V4L2 has two-tier driver architecture. T

23、he upper is videodev module. When the videodev has been initialized, it registers itself as a character device of major number 81, and their own characters driver member functions are registered simultaneously. The lower is V4L2 driver, videodev client in fact, which can be called by Videodev throug

24、h V4L2 driver member functions. After V4L2 driver is initialized, the structure including V4L2 driver member functions, minor number and other related information is passed to videodev, consequently, the device to be handled is registered to videodev. When V4L2 driver is being initialized, first of

25、all, system device to be processed is enumerated; then, the structure v4l2_device is added for each device, and the pointer directing to the structure v4l2_device is passed to v4l2_register_device(),which calls initialization functions of v4l2_device to initialize devices. Before calling v4l2_regist

26、er_device(), the information of name, type, minor number and open function must be added to driver. When a driver is touched off by applications, thecontrol will firstly be delivered to the functions of videodev, videodev has responsibility to transform file or node structure pointer passed by appli

27、cations to V4L2 structure pointer, and calls processing functions of V4L2 driver. 2) Image acquisition based on V4L2 The main steps of video capture of V4L2 are as follows: a) open video device v4l2_fd = open(V4L2_DEV_NODE, O_RDWR); open /dev/video0; fb_fd = open(FB_DEV_NODE, O_RDWR); open frambuffe

28、r; b) device initialization Query the device properties and get function supported by VIDIOC_QUERYCAP; set picture format using VIDIOC_S_FMT; allocate memory buffer in the kernel space and user space respectively through VIDIOC_REQBUFS and malloc(),and finally utilize mmap() for memory mapping. c) i

29、mage acquisition and display Start and stop acquisition by VIDIOC_STREAMON and IDIOC_STREAMOFF. There are two ways for video acquisition: memory mapping and reading data directly from device. Image collection by double cache through mmap() is used here. Compile preview function v4l2_show_on_fb(v4l2_

30、fd,fbmem, preview_frames) to preview the pictures. d) close video device 3) Close the device through close() . The flow chart of image acquisition based on V4L2 is as figure 2: There are two important system calls for V4L2 during video acquisition :ioctl() and mmap(). a) main itctl() command ioctl()

31、 is a powerful function. It can control the I/O channels of equipment, set the format of video and frame, and also can inquiry current device properties. Main ioctl commands are shown as table I: Header files such as include/linux/videodev2.h or videodev.h can be added to the kernel to achieve the a

32、bove function calls. b) memory mapping mmap() There are two ways to capture the video image: one is read() for reading directly, and the other is mmap() for memory mapping. Mmap() gives a chance for sharing memory between processes through mapping a common file. After a general file is mapped to the

33、 address space of process, the file can be accessed by processes as ordinary memory, that is, the memory can be read and wrote directly, and there is no need to call read() and write(),it can accelerate I/O access. In the third step of image acquisition above, data copy is replaced by multiple cache

34、 for image collection through mmap() to improve efficiency. Two image buffers are created in the kernel space, when applications need images, data will be shared by mapping the kernel buffer to user space through mmap(). The process of video image collection using double frame buffer is as follows:

35、First, request image buffer through VIDIOC_REQBUFS; second, call mmap() twice to create corresponding relation between user space and kernel space buffer; third, add the buffer to collection sequence beside driver by VIDIOC_QBUF; fourth, start to gather image and place them in the buffer zone using

36、VIDIOC_STREAMON; fifth, VIDIOC_STREAMOFF is called to stop collecting image. At this point, the driver will automatically remove all the buffers from image acquisition sequence, and clear all the memory mappings by munmap(). Note: before reading buffer zone, VIDIOC_DQBUG should be called at first to

37、 notice that the buffer is unavailable, or it will lead to inconsistence of relating images. IV. RESULT AND PROSPECT The following figure 3 shows the hardware platform and the result of experiment. The collecting picture, whose size is 400480, displayed on the LCD clearly. Based on Linux platform, t

38、he image is collected by CMOS camera and previewed successfully using image acquisition applications on the base of V4L2.During the operation in actual, the pictures display well and have good quality. The advantages of the system are good scalability and extensive use, and some reference value is s

39、upplied for relevant areas of video image acquisition. For the next step, it is hoped that the picture gathered will be encoded and transmitted to PC to realize video surveillance. ACKNOWLEDGEMENTWe wish to thank Professor Huang Zhiwei of Department of Electrical Engineering at University of South C

40、hina for his encouragement and support on this paper. Besides, we also appreciate seniors at the laboratory for their suggestion and proofreading spelling for the paper. 中文翻译基于V4L2嵌入式图像采集的实现李路银，李玉红，张鹏鹏物理电子学，南华大学电机工程系中国，衡阳luyinli198755,tianqing924 摘要如今有一个观点：在嵌入式Linux中基于V4L2的图像采集应用还较少。本系统介绍的基于V4L2嵌入式图

41、像采集系统是由s3c6410作为硬件开发平台，Linux为软件平台，然后加载CMOS摄像头OV9650和其他相关的驱动程序设计完成的。图像采集应用是基于V4L2完成的，采用双帧缓冲来减少CPU利用率，实现采集和预览图像。实现了400480大小，每秒15帧的帧速率图像采集。采集的图像显示清晰，具有良好的品质。实验结果表明，系统具有良好的可扩展性，它提供了嵌入式手持设备的一个新的方案。关键词：v4l2；OV9650；图像采集；S3C6410；双帧缓冲1.简介如今视频图像处理技术被广泛应用在电子技术和计算机技术中。从相机或其他的图像采集设备通过数学变换来获取的数字图像信息，然后经过编码、滤波、增强、

42、恢复、压缩、存储和其他过程由计算机进行处理生成可视化的图像和其他结果。随着嵌入式技术的发展，目前从模拟转换到数字图像采集技术越来越成熟。其中，嵌入式图像采集，以其优越的性能吸引了越来越多的人的关注。嵌入式微处理器是因为其高性能的图像处理系统，较低的成本，低功耗的成为最佳选择。三星S3C6410为 ARM11内核，采用64/32位的内部总线架构。它还包括许多强大的硬件加速器，如运动视频处理，音频处理等。一个集成的MFC（多格式编解码器）支持编码和解码，支持VC1、MPEG4 / H.263/H.264的解码，所以它是很方便的进行图像处理。利用S3C6410为核心的嵌入式硬件平台，本文设计支持V4

43、L2和OV9650摄像头驱动的Linux内核，并应用于该硬件平台，实现图像采集应用。使用双帧缓冲，以降低功耗，最终，系统实现采集图片并显示在液晶显示屏上。2.硬件系统结构整个图像采集系统主要包括CMOS摄像头OV9650，核心控制器S3C6410，液晶和其他外设。显示系统的硬件结构如图1所示：图1 通用硬件平台A.处理器：基于三星S3C6410 ARM1176JZF-S内核，其频率是533MHz/667MHz，包括用于媒体处理的SIMD（单指令多数据）。它工作于特殊的工作方式，以使其适合用于视频处理。B.相机：这里使用的是OmniVision的OV9650。它集成了一个10位A / D转换器，

44、相应的数据输出接口为：D 0:9。输出图像数据格式可以是原始RGB 10位或通过内部DSP处理后的8位RGB / YCbCr图像。该相机接口支持ITU-BT 601/656的YCbCr 8位模式。OV9650的输出口为D 9:2应该被连接到S3C6410的数据接口。C.外设：这部分主要包括LCD和触摸屏接口电路，JTAG调试电路，复位电路，电源电路，RS232串行接口电路等。因为OV9650寄存器控制协议串行相机控制总线（SCCB）可与I2C兼容的，所以我们使用I2C来模拟SCCB用于配置OV9650内部寄存器。3.软件设计图像采集的实现需要两个步骤：首先，将相关的底层驱动程序加载到Linux

45、内核;其次，编译顶层的图像采集应用用于的图像数据的采集，并显示在LCD终端。A.相关的驱动程序加载编译应用程序与驱动程序有关，所以应该首先加载驱动程序。由于采用内核驱动程序，所以只需添加相关配置到内核中即可。1）内核配置：在内核代码的目录，使用命令“make menuconfig”进行内核配置：为Linux选择设备驱动程序，多媒体设备视频加载video4linux模块为视频设备的编程提供接口，选择的多媒体设备后为相机OV965x提供支持，并且使内核支持CMOS图像传感器设备驱动。保存配置并退出。2）生成内核映像使用下面的命令：make dep的：读取配置文件或创造相应的配置，以确定编译的zIm

46、age：生成的内核映像可以支持V4L2和OV9650及其依赖关系树。当内核启动时，如果存在如下所示额相同信息，它表明OV9650驱动程序已经被成功加载：CAM OV9650 init reg start. CAM OV9650 init reg end. 系统启动后，它可以自动识别OV9650，通过系统调用可以获取设备信息，便于应用开发，系统提供I/ O操作函数接口，可以实现对CMOS图像传感器相关操作。B.图像采集应用V4L是Linux的视频设备应用程序提供的接口，通过使用API函数可以从视频设备中读出图像数据。1）V4L2驱动结构V4L有两个缺点：驱动程序设计时，不能在同一时间打开多个设备

47、，此外，V4L的 API不能很好地支持设备编码能力。比尔德克斯在这种情况下，重新设计了一套API和数据结构，称为V4L 第二版的，可扩展性和灵活性得到改善，支持越来越多的视频设备。V4L2是V4L的更新版本，V4L2已经作为Linux2.6内核驱动协议。V4L2作为Linux视频采集设备驱动程序的规范，V4L2采用分层的方法，为驱动程序开发提供明确和一致的接口：应用程序是在顶层，V4L2在中间层，而其他硬件设备在底层。V4L2有两层驱动架构：上层是videodev模块。当videodev寄存器被初始化，主设备号81注册成为一个字符设备，并同时注册了自己的字符驱动程序的成员函数。下层是V4L2驱

48、动，事实上是videodev的客户端，它是可以由Videodev通过V4L2驱动程序调用的成员函数组成。V4L2驱动程序初始化后，V4L2驱动程序的成员函数，次要设备号以及其他相关信息的结构被传递到videodev中，至此，被处理的移动设备注册到videodev。当V4L2驱动正在初始化时，首先应在结构体v4l2_device中添加每个设备，并初始化结构体v4l2_device的指针，然后指针被传递到v4l2_register_device（）函数中，最后调用初始化函数的v4l2_device初始化设备。在调用v4l2_register_device（）之前，信息名称，类型，次设备名和开放的功能必须先添加驱动程序中。当应用程序开始时，首先设备控制权将传送给videodev的函数，videodev有权利转换的文件或应用程序到V4L