v4l2 打开摄像头，ioctl 发送VIDIOC_DQBUF命令返回-1，错误码62：Timer expired

[RwinR]

这两天在琢磨用v4l2框架开启摄像头，遇到了解决不了的问题，在百度上也搜不到相关解决办法，求各位前辈指教。

我写的代码执行到发送命令VIDIOC_DQBUF获取帧数据的时候，返回-1，提示错误信息Timer expired，

我申请的的缓冲区个数是三个，取第一个缓冲区数据失败，第二个第三个会成功，但是取到的数据写到jpg文件在电脑上无法显示。

代码如下：

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <linux/videodev2.h>
#include <strings.h>
#include <unistd.h>
#include <errno.h>
#include <sys/ioctl.h>

struct buf_inf
{
	void *start;
	int length;
};


int main()
{
	int i,ret,camfd;
	char jpgpath[10];

	camfd = open("/dev/video7",O_RDWR);
	if(camfd == -1)
	{
		perror("打开摄像头驱动失败\n");
		return -1;
	}

	//获取摄像头功能参数
	struct v4l2_capability cam_cap;
	bzero(&cam_cap,sizeof(cam_cap));
	ret = ioctl(camfd,VIDIOC_QUERYCAP,&cam_cap);
	if(ret == -1)
	{
		perror("获取摄像头功能参数失败\n");
		return -1;
	}

	printf("version:%d\n",cam_cap.version);

	//设置摄像头通道
	int channel=0;
	ret = ioctl(camfd,VIDIOC_S_INPUT,&channel);
	if(ret == -1)
	{
		perror("设置摄像头通道失败\n");
		return -1;
	}

	//获取摄像头的采集格式
	struct v4l2_format cam_fmt;
	bzero(&cam_fmt,sizeof(cam_fmt));
	cam_fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	ret = ioctl(camfd,VIDIOC_G_FMT,&cam_fmt);
	if(ret == -1)
	{
		perror("获取摄像头采集格式失败\n");
		return -1;
	}
	printf("摄像头当前的宽为：%d 高为：%d\n",cam_fmt.fmt.pix.width,cam_fmt.fmt.pix.height);

	//设置摄像头采集格式
	bzero(&cam_fmt,sizeof(cam_fmt));
	cam_fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	cam_fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_MJPEG;
	cam_fmt.fmt.pix.width = 640;
	cam_fmt.fmt.pix.height = 480;
	ret = ioctl(camfd,VIDIOC_S_FMT,&cam_fmt);
	if(ret == -1)
	{
		perror("设置摄像头采集格式失败\n");
		return -1;
	}
	printf("摄像头当前的宽为：%d 高为：%d\n",cam_fmt.fmt.pix.width,cam_fmt.fmt.pix.height);


	//申请缓冲块
	struct v4l2_requestbuffers cam_bufs;
	bzero(&cam_bufs,sizeof(cam_bufs));
	cam_bufs.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	cam_bufs.memory = V4L2_MEMORY_MMAP;
	cam_bufs.count = 3;
	
	ret = ioctl(camfd,VIDIOC_REQBUFS,&cam_bufs);
	if(ret == -1)
	{
		perror("申请缓冲块失败\n");
		return -1;
	}

	//分配缓冲块
	struct buf_inf *cam_inf = calloc(cam_bufs.count,sizeof(struct buf_inf));
	for(i=0; i<cam_bufs.count; i++)
	{
		struct v4l2_buffer cam_buf;
		bzero(&cam_buf,sizeof(cam_buf));
		cam_buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		cam_buf.memory = V4L2_MEMORY_MMAP;
		cam_buf.index = i;

		ret = ioctl(camfd,VIDIOC_QUERYBUF,&cam_buf);
		if(ret == -1)
		{
			perror("分配缓冲块失败\n");
			return -1;
		}

		//把分配到的内存映射到自定义的空间（保存首地址，方便使用）
		cam_inf[i].start = mmap(NULL, cam_buf.length, PROT_WRITE|PROT_READ, MAP_SHARED,camfd, cam_buf.m.offset);
		if(cam_inf[i].start == NULL)
		{
			perror("映射内存失败\n");
		}

		cam_inf[i].length = cam_buf.length;
	}

	//将帧数据放到缓存（入队）
	for(i=0; i<cam_bufs.count; i++)
	{
		struct v4l2_buffer cam_buf;
		bzero(&cam_buf,sizeof(cam_buf));
		cam_buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		cam_buf.memory = V4L2_MEMORY_MMAP;
		cam_buf.index = i;

		ret = ioctl(camfd,VIDIOC_QBUF,&cam_buf);
		if(ret == -1)
		{
			perror("入队失败\n");
			return -1;
		}
	}

	//开启摄像头，采集数据
	enum v4l2_buf_type cam_type1 = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	ret = ioctl(camfd,VIDIOC_STREAMON,&cam_type1);
	if(ret == -1)
	{
		perror("开启摄像头失败\n");
		return -1;
	}

	//将缓冲块中的帧数据拿出来保存到空白的JPG文件中
	for(i=0; i<cam_bufs.count; i++)
	{
		struct v4l2_buffer cam_buf1;
		bzero(&cam_buf1,sizeof(cam_buf1));
		cam_buf1.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		cam_buf1.memory = V4L2_MEMORY_MMAP;
		cam_buf1.index = i;

		printf("出队%d\n",i);
		ret = ioctl(camfd,VIDIOC_DQBUF,&cam_buf1);
		if(ret == -1)
		{
			perror("出队失败\n");
			printf("errno:%d\n",errno);
			continue;
		}

		sprintf(jpgpath,"%d.jpg",i);
		int fd = open(jpgpath,O_CREAT|O_TRUNC|O_RDWR);
		if(fd == -1)
		{
			perror("创建jpg文件失败\n");
			return -1;
		}

		write(fd,cam_inf[i].start,cam_inf[i].length);
		
		close(fd);
	}

	//关闭摄像头，停止采集数据
	ret = ioctl(camfd,VIDIOC_STREAMOFF,&cam_type1);
	if(ret == -1)
	{
		perror("关闭摄像头失败\n");
		return -1;
	}

	return 0;
}

运行结果如下
version:197671
摄像头当前的宽为：640 高为：480
摄像头当前的宽为：640 高为：480
出队0
出队失败
: Timer expired
errno:62
出队1
出队2