基于v4l2嵌入式圖像采集的實現(xiàn)畢業(yè)論文外文翻譯(編輯修改稿)
2025-09-06 17:22 本頁面
【文章內(nèi)容簡介】 4L2 in the middle layer, while he actual hardware device on the bottom. V4L2 has twotier driver architecture. The 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 through 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 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_register_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 applications 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 frambuffer。 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) image 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_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() mand ioctl() 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 mands are shown as table I: Header files such as include/linux/ or can be added to the kernel to achieve the above 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 mon file. After a general file is mapped to the address space of process, the file can be accessed by processes as ordinary
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