摄像头程序详解
2014-05-02 19:07
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程序名:usbcamera.cpp Makefile: usbcamera: usbcamera.cpp arm-linux-g++ usbcamera.cpp -Wall -O2 -o usbcamera arm-linux-strip -s usbcamera clean: rm usbcamera 可执行文件:usbcamera 使用方法:将可执行文件下载到开发板,执行,会在当前文件夹生成一张图片。 #include <stdio.h> #include <stdlib.h> #include <string.h> #include <assert.h> #include <getopt.h> #include <fcntl.h> #include <unistd.h> #include <errno.h> #include <malloc.h> #include <sys/stat.h> #include <sys/types.h> #include <sys/time.h> #include <sys/mman.h> #include <sys/ioctl.h> #include <asm/types.h> #include <linux/videodev2.h> #define CLEAR(x) memset (&(x), 0, sizeof (x)) struct buffer { void * start; size_t length; }; static char * dev_name = "/dev/video0";//摄像头设备名 static int fd = -1; struct buffer * buffers = NULL; static unsigned int n_buffers = 0; FILE *file_fd; static unsigned long file_length; static unsigned char *file_name; ////////////////////////////////////////////////////// //获取一帧数据 ////////////////////////////////////////////////////// static int read_frame (void) { struct v4l2_buffer buf; unsigned int i; CLEAR (buf); buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; /*8.出队列以取得已采集数据的帧缓冲,取得原始采集数据。VIDIOC_DQBUF*/ int ff = ioctl (fd, VIDIOC_DQBUF, &buf); if(ff<0) printf("failture\n"); //出列采集的帧缓冲 assert (buf.index < n_buffers); printf ("buf.index dq is %d,\n",buf.index); fwrite(buffers[buf.index].start, buffers[buf.index].length, 1, file_fd); //将其写入文件中 /*9.将缓冲重新入队列尾,这样可以循环采集。VIDIOC_QBUF*/ ff=ioctl (fd, VIDIOC_QBUF, &buf); //再将其入列 if(ff<0)//把数据从缓存中读取出来 printf("failture VIDIOC_QBUF\n"); return 1; } int main (int argc,char ** argv) { struct v4l2_capability cap; struct v4l2_format fmt; unsigned int i; enum v4l2_buf_type type; file_fd = fopen("test-mmap.jpg", "w");//图片文件名 /*1.打开设备文件。 int fd=open(”/dev/video0″,O_RDWR);*********/ fd = open (dev_name, O_RDWR /* required */ | O_NONBLOCK, 0);//打开设备 /*2.取得设备的capability,看看设备具有什么功能,比如是否具有视频输入,或者音频输入输出等。VIDIOC_QUERYCAP,struct v4l2_capability*/ int ff=ioctl (fd, VIDIOC_QUERYCAP, &cap);//获取摄像头参数 if(ff<0) printf("failture VIDIOC_QUERYCAP\n"); /*3.设置视频的制式和帧格式,制式包括PAL,NTSC,帧的格式个包括宽度和高度等。*/ struct v4l2_fmtdesc fmt1; int ret; memset(&fmt1, 0, sizeof(fmt1)); fmt1.index = 0; fmt1.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; //获取当前驱动支持的视频格式 while ((ret = ioctl(fd, VIDIOC_ENUM_FMT, &fmt1)) == 0) { fmt1.index++; printf("{ pixelformat = '%c%c%c%c', description = '%s' }\n",fmt1.pixelformat & 0xFF, (fmt1.pixelformat >> 8) & 0xFF,(fmt1.pixelformat >> 16) & 0xFF, (fmt1.pixelformat >> 24) & 0xFF,fmt1.description); } //帧的格式,比如宽度,高度等 CLEAR (fmt); fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; //数据流类型,必须永远是V4L2_BUF_TYPE_VIDEO_CAPTURE fmt.fmt.pix.width = 640;//宽,必须是16的倍数 fmt.fmt.pix.height = 480;////高,必须是16的倍数 fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_JPEG;//视频数据存储类型//V4L2_PIX_FMT_YUYV;//V4L2_PIX_FMT_YVU420;//V4L2_PIX_FMT_YUYV; fmt.fmt.pix.field = V4L2_FIELD_INTERLACED; //设置当前驱动的频捕获格式 ff = ioctl (fd, VIDIOC_S_FMT, &fmt); if(ff<0) printf("failture VIDIOC_S_FMT\n"); //计算图片大小 file_length = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height; /*4.向驱动申请帧缓冲,一般不超过5个。struct v4l2_requestbuffers*/ struct v4l2_requestbuffers req; CLEAR (req); req.count = 1;//缓存数量,也就是说在缓存队列里保持多少张照片 req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; req.memory = V4L2_MEMORY_MMAP;//或V4L2_MEMORY_USERPTR ff = ioctl (fd, VIDIOC_REQBUFS, &req); //申请缓冲,count是申请的数量 if(ff<0) printf("failture VIDIOC_REQBUFS\n"); if (req.count < 1) printf("Insufficient buffer memory\n"); buffers = (struct buffer*)calloc (req.count, sizeof (*buffers));//内存中建立对应空间 /*5.将申请到的帧缓冲映射到用户空间,这样就可以直接操作采集到的帧了,而不必去复制。mmap*/ for (n_buffers = 0; n_buffers < req.count; ++n_buffers) { struct v4l2_buffer buf; //驱动中的一帧 CLEAR (buf); buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; buf.index = n_buffers; //把VIDIOC_REQBUFS中分配的数据缓存转换成物理地址 if (-1 == ioctl (fd, VIDIOC_QUERYBUF, &buf)) //映射用户空间 printf ("VIDIOC_QUERYBUF error\n"); buffers[n_buffers].length = buf.length; buffers[n_buffers].start = mmap (NULL /* start anywhere */,buf.length,PROT_READ | PROT_WRITE /* required */,MAP_SHARED /* recommended */,fd, buf.m.offset);//通过mmap建立映射关系,返回映射区的起始地址 if (MAP_FAILED == buffers[n_buffers].start) printf ("mmap failed\n"); } /*6.将申请到的帧缓冲全部入队列,以便存放采集到的数据.VIDIOC_QBUF,struct v4l2_buffer*/ for (i = 0; i < n_buffers; ++i) { struct v4l2_buffer buf; CLEAR (buf); buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; buf.memory = V4L2_MEMORY_MMAP; buf.index = i; //把数据从缓存中读取出来 if (-1 == ioctl (fd, VIDIOC_QBUF, &buf))//申请到的缓冲进入列队 printf ("VIDIOC_QBUF failed\n"); } type = V4L2_BUF_TYPE_VIDEO_CAPTURE; /*7.开始视频的采集。VIDIOC_STREAMON*/ if (-1 == ioctl (fd, VIDIOC_STREAMON, &type)) //开始捕捉图像数据 printf ("VIDIOC_STREAMON failed\n"); for (;;) //这一段涉及到异步IO { fd_set fds; struct timeval tv; int r; FD_ZERO (&fds);//将指定的?件描述符集清空 FD_SET (fd, &fds);//在文件描述符集合中增鍔????个新的文件描述符 /* Timeout. */ tv.tv_sec = 2; tv.tv_usec = 0; r = select (fd + 1, &fds, NULL, NULL, &tv);//判断是否可读(即摄像头是否准备好),tv是定时 if (-1 == r) { if (EINTR == errno) continue; printf ("select err\n"); } if (0 == r) { fprintf (stderr, "select timeout\n"); exit (EXIT_FAILURE); } if (read_frame ())//如果可读,执行read_frame ()函数,并跳出循环 break; } unmap: for (i = 0; i < n_buffers; ++i) if (-1 == munmap (buffers->start, buffers->length)) printf ("munmap error"); type = V4L2_BUF_TYPE_VIDEO_CAPTURE; /*10.停止视频的采集。VIDIOC_STREAMOFF*/ if (-1 == ioctl(fd, VIDIOC_STREAMOFF, &type)) printf("VIDIOC_STREAMOFF"); /*11.关闭视频设备。close(fd);*/ close (fd); fclose (file_fd); exit (EXIT_SUCCESS); return 0; }
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