[经验]

【NanoPi NEO2试用体验】NEO2使用uvc摄像头

2017-6-17 10:17:58

3681 摄像头

uvc摄像头就是最常用的u***免驱摄像头，Linux内核都支持，但是有的内核并没有把uvc编译进内核而是以module的形式提供，需要使用modprobe uvcvideo安装驱动，或者配置内核吧uvc配置成编译进内核重新烧写系统。

使用uvc摄像头和使用其他设备一样都是打开设备文件然后使用ioctl进行摄像头的参数获取和配置，配置代码如下：

int VideoInit(struct VideoDev *video)
{
unsigned int i;
int ret;
//帧的格式，比如宽度，高度等
CLEAR (video->format);
video->format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; //数据流类型，必须永远是V4L2_BUF_TYPE_VIDEO_CAPTURE
video->format.fmt.pix.width = 640;//宽，必须是16的倍数
video->format.fmt.pix.height = 480;//高，必须是16的倍数
video->format.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;//视频数据存储类型//V4L2_PIX_FMT_YUYV;//V4L2_PIX_FMT_YVU420;//V4L2_PIX_FMT_YUYV;
video->format.fmt.pix.field = V4L2_FIELD_INTERLACED;
//设置当前驱动的频捕获格式
ret = ioctl (video->fd, VIDIOC_S_FMT, &video->format);
if(ret < 0)
{
printf("failture VIDIOC_S_FMTn");
return -1;
}
/*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 = 4;//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
ret = ioctl (video->fd, VIDIOC_REQBUFS, &req); //申请缓冲，count是申请的数量
if(ret < 0)
printf("failture VIDIOC_REQBUFSn");
if (req.count < 1)
printf("Insufficient buffer memoryn");
video->buffers = (struct buffer *)calloc (req.count, sizeof (struct buffer)); //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 (video->n_buffers = 0; video->n_buffers < req.count; ++video->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 = video->n_buffers;
//把VIDIOC_REQBUFS中分配的数据缓存转换成物理地址
if (-1 == ioctl (video->fd, VIDIOC_QUERYBUF, &buf)) //映射用户空间
printf ("VIDIOC_QUERYBUF errorn");
video->buffers[video->n_buffers].length = buf.length;
video->buffers[video->n_buffers].start = mmap (NULL /* start anywhere */, buf.length, PROT_READ | PROT_WRITE /* required */, MAP_SHARED /* recommended */, video->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 == video->buffers[video->n_buffers].start)
printf ("mmap failedn");
}
/*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 < video->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 (video->fd, VIDIOC_QBUF, &buf))//申请到的缓冲进入列队
printf ("VIDIOC_QBUF failedn");
}
}

复制代码

获取一帧图像可以根据摄像头支持的图片格式获取，我这里的摄像头比较low，只支持30万像素的yuyv格式，采集图像代码如下：

int VideoGetFrame(struct VideoDev *video,unsigned char *image_buf)
{
struct v4l2_buffer buf;
unsigned int i;
int ret;
CLEAR (buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
ret = ioctl (video->fd, VIDIOC_DQBUF, &buf);
if(ret < 0)
printf("failture VIDIOC_DQBUFn"); //出列采集的帧缓冲
// printf ("buf.index dq is %d,n", buf.index);
/*9.将缓冲重新入队列尾,这样可以循环采集。VIDIOC_QBUF*/
ret = ioctl (video->fd, VIDIOC_QBUF, &buf); //再将其入列
if(ret < 0) //把数据从缓存中读取出来
printf("failture VIDIOC_QBUFn");
// fwrite(video->buffers[buf.index].start, video->buffers[buf.index].length, 1, file_fd); //将其写入文件中
if(image_buf != NULL) //如果image_buf不为空的话则进行数据拷贝
memcpy(image_buf,video->buffers[buf.index].start,video->buffers[buf.index].length);
return video->buffers[buf.index].length;
}