USB Camera(C270) 支持MJPEG和YUYV格式的图像输出，这里采用YUYV(YUV422) 转化成 RGB32，然后在LCD显示出来
帧率设置成30时，分辨率设置成640X480， CPU占用 几乎达到100%
帧率设置成10时，分辨率设置成320X240， CPU占用 如下：
Mem: 11764K used, 501476K free, 0K shrd, 216K buff, 3272K cachedCPU: 19.1% usr 0.0% sys 0.0% nic 80.8% idle 0.0% io 0.0% irq 0.0% sirqLoad average: 0.67 0.42 0.20 1/35 871 PID PPID USERSTAT VSZ %VSZ CPU %CPU COMMAND 870 831 0S3748 0.7 0 18.9 ./cam_preview 8311 0S3036 0.5 0 0.0 -/bin/sh 871 831 0R3036 0.5 0 0.0 top10 0S3032 0.5 0 0.0 {linuxrc} init 3892 0SW0 0.0 0 0.0 [kworker/0:1]62 0SW0 0.0 0 0.0 [kworker/u:0] 112 0SW0 0.0 0 0.0 [watchdog/0]82 0SW0 0.0 0 0.0 [rcu_preempt] 2842 0SW0 0.0 0 0.0 [khubd] 6802 0SW0 0.0 0 0.0 [mmcqd/0]20 0SW0 0.0 0 0.0 [kthreadd]32 0SW0 0.0 0 0.0 [ksoftirqd/0]52 0SW<0 0.0 0 0.0 [kworker/0:0H]72 0SW<0 0.0 0 0.0 [kworker/u:0H]92 0SW0 0.0 0 0.0 [rcu_bh] 102 0SW0 0.0 0 0.0 [rcu_sched] 122 0SW<0 0.0 0 0.0 [khelper] 132 0SW0 0.0 0 0.0 [kworker/u:1] 2702 0SW0 0.0 0 0.0 [bdi-default] 2722 0SW<0 0.0 0 0.0 [kblockd]帧率设置成10时，分辨率设置成640X480， CPU占用 如下：Mem: 13916K used, 499324K free, 0K shrd, 212K buff, 3256K cachedCPU: 84.9% usr 0.2% sys 0.0% nic 14.8% idle 0.0% io 0.0% irq 0.0% sirqLoad average: 0.55 0.21 0.10 3/35 869 PID PPID USERSTAT VSZ %VSZ CPU %CPU COMMAND 868 831 0R5540 1.0 0 85.0 ./cam_preview 8311 0S3036 0.5 0 0.0 -/bin/sh 869 831 0R3036 0.5 0 0.0 top10 0S3032 0.5 0 0.0 {linuxrc} init 3892 0SW0 0.0 0 0.0 [kworker/0:1]62 0SW0 0.0 0 0.0 [kworker/u:0] 112 0SW0 0.0 0 0.0 [watchdog/0]82 0RW0 0.0 0 0.0 [rcu_preempt] 2842 0SW0 0.0 0 0.0 [khubd] 6802 0SW0 0.0 0 0.0 [mmcqd/0]20 0SW0 0.0 0 0.0 [kthreadd]32 0SW0 0.0 0 0.0 [ksoftirqd/0]52 0SW<0 0.0 0 0.0 [kworker/0:0H]72 0SW<0 0.0 0 0.0 [kworker/u:0H]92 0SW0 0.0 0 0.0 [rcu_bh] 102 0SW0 0.0 0 0.0 [rcu_sched] 122 0SW<0 0.0 0 0.0 [khelper] 132 0SW0 0.0 0 0.0 [kworker/u:1] 2702 0SW0 0.0 0 0.0 [bdi-default] 2722 0SW<0 0.0 0 0.0 [kblockd]测试代码如下：#include <stdio.h>#include <string.h>#include <errno.h>#include <stdlib.h>#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <time.h>#include <sys/mman.h>#include <assert.h>#include <linux/videodev2.h>#include <linux/fb.h>//照相机延时等待#define TimeOut 5 //拍照 个数#define CapNum 10//设置照片宽度 高度#define CapWidth 320#define CapHeight 240//申请Buf个数#define ReqButNum 4//使用前置或者后置Camera 前置设0，后置设1#define IsRearCamera 0//设置帧率#define FPS 10//设置格式#define PIXELFMT V4L2_PIX_FMT_YUYV#define CapDelay 0*500*1000#define CLEAR(x) memset(&(x), 0, sizeof(x))typedef unsigned char BYTE;typedef unsigned short WORD;typedef unsigned int DWORD;typedef long LONG;typedef struct{void *start;int length;}BUFTYPE;BUFTYPE *user_buf;static int n_buffer = 0;static struct fb_var_screeninfo vinfo;static struct fb_fix_screeninfo finfo;static int lcd_buf_size;static char *fb_buf = NULL;//打开摄像头设备int open_camer_device(){int fd;//非阻塞方式打开，如果打开错误，会立即返回if((fd = open("/dev/video0",O_RDWR | O_NONBLOCK)) < 0){perror("Fail to open");exit(EXIT_FAILURE);} printf("open cam success %d\n",fd);return fd;}//打开摄像头设备int open_lcd_device(){int fd;//非阻塞方式打开，如果打开错误，会立即返回if((fd = open("/dev/fb0",O_RDWR | O_NONBLOCK)) < 0){perror("Fail to open");exit(EXIT_FAILURE);} printf("open lcd success %d\n",fd);return fd;}//申请Camera Buf，并映射到用户空间，，利用全局变量user_buf保存映射信息int init_mmap(int lcd_fd, int cam_fd){int i = 0;int err;int ret;struct v4l2_control ctrl;struct v4l2_requestbuffers reqbuf;//mmap framebufferfb_buf = (char *)mmap(NULL,lcd_buf_size,PROT_READ | PROT_WRITE,MAP_SHARED ,lcd_fd,0);if(NULL == fb_buf){perror("Fail to mmap fb_buf");exit(EXIT_FAILURE);}bzero(&reqbuf,sizeof(reqbuf));reqbuf.count = ReqButNum;reqbuf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;reqbuf.memory = V4L2_MEMORY_MMAP;printf("start VIDIOC_REQBUFS\n");//申请视频缓冲区(这个缓冲区位于内核空间，需要通过mmap映射)//这一步操作可能会修改reqbuf.count的值，修改为实际成功申请缓冲区个数if(-1 == ioctl(cam_fd,VIDIOC_REQBUFS,&reqbuf)){perror("Fail to ioctl ‘VIDIOC_REQBUFS’");exit(EXIT_FAILURE);}n_buffer = reqbuf.count;user_buf = calloc(reqbuf.count,sizeof(*user_buf));if(user_buf == NULL){fprintf(stderr,"Out of memory\n");exit(EXIT_FAILURE);}//将内核缓冲区映射到用户进程空间for(i = 0; i < reqbuf.count; i ++){struct v4l2_buffer buf;bzero(&buf,sizeof(buf));buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;buf.memory = V4L2_MEMORY_MMAP;buf.index = i;//查询申请到内核缓冲区的信息if(-1 == ioctl(cam_fd,VIDIOC_QUERYBUF,&buf)){perror("Fail to ioctl : VIDIOC_QUERYBUF");exit(EXIT_FAILURE);}user_buf[i].length = buf.length;user_buf[i].start =mmap(NULL,/*start anywhere*/buf.length,PROT_READ | PROT_WRITE,MAP_SHARED,cam_fd,buf.m.offset);if(MAP_FAILED == user_buf[i].start){perror("Fail to mmap\n");printf("%d\n",i);exit(EXIT_FAILURE);}//printf("start:08%lx\n",user_buf[i].start);}return 0;}//初始化视频设备int init_device(int lcd_fd, int cam_fd){struct v4l2_fmtdesc fmt;struct v4l2_capability cap;struct v4l2_format stream_fmt;struct v4l2_input input;struct v4l2_control ctrl;struct v4l2_streamparm stream;int err;int ret;if(-1 == ioctl(lcd_fd,FBIOGET_FSCREENINFO,&finfo)){perror("Fail to ioctl:FBIOGET_FSCREENINFO\n");exit(EXIT_FAILURE);}if (-1==ioctl(lcd_fd, FBIOGET_VSCREENINFO, &vinfo)) {perror("Fail to ioctl:FBIOGET_VSCREENINFO\n");exit(EXIT_FAILURE);}lcd_buf_size = vinfo.xres * vinfo.yres * vinfo.bits_per_pixel / 8;printf("vinfo.xres:%d, vinfo.yres:%d, vinfo.bits_per_pixel:%d, lcd_buf_size:%d, finfo.line_length:%d\n",vinfo.xres, vinfo.yres, vinfo.bits_per_pixel, lcd_buf_size, finfo.line_length);memset(&fmt,0,sizeof(fmt));fmt.index = 0;fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;//枚举视频设置支持的格式while((ret = ioctl(cam_fd,VIDIOC_ENUM_FMT,&fmt)) == 0){fmt.index ++ ;printf("{pixelformat = %c%c%c%c},description = ‘%s’\n",fmt.pixelformat & 0xff,(fmt.pixelformat >> 8)&0xff,(fmt.pixelformat >> 16) & 0xff,(fmt.pixelformat >> 24)&0xff,fmt.description);}//查询视频设备支持的功能ret = ioctl(cam_fd,VIDIOC_QUERYCAP,&cap);if(ret < 0){perror("FAIL to ioctl VIDIOC_QUERYCAP");exit(EXIT_FAILURE);}if(!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)){printf("The Current device is not a video capture device\n");exit(EXIT_FAILURE);}if(!(cap.capabilities & V4L2_CAP_STREAMING)){printf("The Current device does not support streaming i/o\n");exit(EXIT_FAILURE);}CLEAR(stream_fmt);//设置摄像头采集数据格式，如设置采集数据的//长,宽，图像格式(JPEG,YUYV,MJPEG等格式)stream_fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;stream_fmt.fmt.pix.width = CapWidth;stream_fmt.fmt.pix.height = CapHeight;stream_fmt.fmt.pix.pixelformat = PIXELFMT;stream_fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;if(-1 == ioctl(cam_fd,VIDIOC_S_FMT,&stream_fmt)){printf("Can’t set the fmt\n");perror("Fail to ioctl\n");exit(EXIT_FAILURE);}printf("VIDIOC_S_FMT successfully\n");init_mmap(lcd_fd, cam_fd);//通过S_PARM来设置FPS/* fimc_v4l2_s_parm */ CLEAR(stream);stream.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;stream.parm.capture.capturemode = 0;stream.parm.capture.timeperframe.numerator = 1;stream.parm.capture.timeperframe.denominator = FPS;err = ioctl(cam_fd, VIDIOC_S_PARM, &stream);if(err < 0)printf("FimcV4l2 start: error %d, VIDIOC_S_PARM", err);return 0;}int start_capturing(int cam_fd){unsigned int i;enum v4l2_buf_type type;//将申请的内核缓冲区放入一个队列中for(i = 0;i < n_buffer;i ++){struct v4l2_buffer buf;bzero(&buf,sizeof(buf));buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;buf.memory = V4L2_MEMORY_MMAP;buf.index = i;if(-1 == ioctl(cam_fd,VIDIOC_QBUF,&buf)){perror("Fail to ioctl ‘VIDIOC_QBUF’");exit(EXIT_FAILURE);}}//开始采集数据type = V4L2_BUF_TYPE_VIDEO_CAPTURE;if(-1 == ioctl(cam_fd,VIDIOC_STREAMON,&type)){printf("i = %d.\n",i);perror("Fail to ioctl ‘VIDIOC_STREAMON’");exit(EXIT_FAILURE);}return 0;}inline int clip(int value, int min, int max) {return (value > max ? max : value < min ? min : value); }//将采集好的数据放到文件中int process_image(void *addr,int length){unsigned char* in=(char*)addr;int width=CapWidth;int height=CapHeight;int istride=CapWidth *2;int x,y,j;int y0,u,y1,v,r,g,b;long location=0; //printf("vinfo.xoffset:%d,vinfo.yoffset:%d\n",vinfo.xoffset,vinfo.yoffset);for ( y = 0; y < height; ++y){for (j = 0, x=0; j < width * 2 ; j += 4,x +=2){location = (x+vinfo.xoffset) * (vinfo.bits_per_pixel/8) + (y+vinfo.yoffset) * finfo.line_length;y0 = in[j];u = in[j + 1] – 128;y1 = in[j + 2];v = in[j + 3] – 128;r = (298 * y0 + 409 * v + 128) >> 8;g = (298 * y0 – 100 * u – 208 * v + 128) >> 8;b = (298 * y0 + 516 * u + 128) >> 8;fb_buf[ location + 0] = clip(b, 0, 255);fb_buf[ location + 1] = clip(g, 0, 255);fb_buf[ location + 2] = clip(r, 0, 255);fb_buf[ location + 3] = 255;r = (298 * y1 + 409 * v + 128) >> 8;g = (298 * y1 – 100 * u – 208 * v + 128) >> 8;b = (298 * y1 + 516 * u + 128) >> 8;fb_buf[ location + 4] = clip(b, 0, 255);fb_buf[ location + 5] = clip(g, 0, 255);fb_buf[ location + 6] = clip(r, 0, 255);fb_buf[ location + 7] = 255;}in +=istride;}//usleep(500);return 0;}int read_frame(int cam_fd){struct v4l2_buffer buf;unsigned int i;bzero(&buf,sizeof(buf));buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;buf.memory = V4L2_MEMORY_MMAP;//从Camera buf中把数据拿出来if(-1 == ioctl(cam_fd,VIDIOC_DQBUF,&buf)){perror("Fail to ioctl ‘VIDIOC_DQBUF’");exit(EXIT_FAILURE);}assert(buf.index < n_buffer);process_image(user_buf[buf.index].start,user_buf[buf.index].length);//把处理过的Buf 重新入队if(-1 == ioctl(cam_fd,VIDIOC_QBUF,&buf)){perror("Fail to ioctl ‘VIDIOC_QBUF’");exit(EXIT_FAILURE);}return 1;}//利用select 进行超时处理int mainloop(int cam_fd){ int count = 1;//CapNum;clock_t startTime, finishTime;double selectTime, frameTime;while(count++ > 0){for(;;){fd_set fds;struct timeval tv;int r;//startTime = clock();FD_ZERO(&fds);FD_SET(cam_fd,&fds);/*Timeout*/tv.tv_sec = TimeOut;tv.tv_usec = 0;r = select(cam_fd + 1,&fds,NULL,NULL,&tv);if(-1 == r){if(EINTR == errno)continue;perror("Fail to select");exit(EXIT_FAILURE);}if(0 == r){fprintf(stderr,"select Timeout\n");exit(EXIT_FAILURE);}startTime = clock();if(read_frame(cam_fd)){finishTime = clock();//printf("delta:%dms\n", (finishTime – startTime)/1000);break;}}//usleep(CapDelay);}return 0;}void stop_capturing(int cam_fd){enum v4l2_buf_type type;type = V4L2_BUF_TYPE_VIDEO_CAPTURE;if(-1 == ioctl(cam_fd,VIDIOC_STREAMOFF,&type)){perror("Fail to ioctl ‘VIDIOC_STREAMOFF’");exit(EXIT_FAILURE);}return;}void uninit_camer_device(){unsigned int i;for(i = 0;i < n_buffer;i ++){if(-1 == munmap(user_buf[i].start, user_buf[i].length)){exit(EXIT_FAILURE);}}if (-1 == munmap(fb_buf, lcd_buf_size)) {perror(" Error: framebuffer device munmap() failed.\n");exit (EXIT_FAILURE) ;}free(user_buf);return;}void close_camer_device(int lcd_fd, int cam_fd){if(-1 == close(lcd_fd)){perror("Fail to close lcd_fd");exit(EXIT_FAILURE);}if(-1 == close(cam_fd)){perror("Fail to close cam_fd");exit(EXIT_FAILURE);}return;}int main(){ int lcd_fd;int cam_fd;lcd_fd = open_lcd_device();cam_fd = open_camer_device();init_device(lcd_fd, cam_fd);//init_mmap(lcd_fd, cam_fd);start_capturing(cam_fd);mainloop(cam_fd);stop_capturing(cam_fd);uninit_camer_device();close_camer_device(lcd_fd, cam_fd);return 0;}
这个社会是存在不公平的，不要抱怨，因为没有用！人总是在反省中进步的！
