linux 开发mipi摄像头示例代码

在Linux下开发mipi摄像头，需要用到V4L2框架，以下是一个简单的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <sys/ioctl.h>
#include <linux/videodev2.h>

#define CAM_DEV "/dev/video0"
#define WIDTH 640
#define HEIGHT 480

int main()
{
    int fd;
    int ret;
    struct v4l2_capability cap;
    struct v4l2_format fmt;
    struct v4l2_requestbuffers reqbuf;
    struct v4l2_buffer buf;

    fd = open(CAM_DEV, O_RDWR);
    if (fd < 0) {
        printf("open %s failed\n", CAM_DEV);
        return -1;
    }

    ret = ioctl(fd, VIDIOC_QUERYCAP, &cap);
    if (ret < 0) {
        printf("VIDIOC_QUERYCAP failed\n");
        close(fd);
        return -1;
    }

    memset(&fmt, 0, sizeof(fmt));
    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    fmt.fmt.pix.width = WIDTH;
    fmt.fmt.pix.height = HEIGHT;
    fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
    fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
    ret = ioctl(fd, VIDIOC_S_FMT, &fmt);
    if (ret < 0) {
        printf("VIDIOC_S_FMT failed\n");
        close(fd);
        return -1;
    }

    memset(&reqbuf, 0, sizeof(reqbuf));
    reqbuf.count = 4;
    reqbuf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    reqbuf.memory = V4L2_MEMORY_MMAP;
    ret = ioctl(fd, VIDIOC_REQBUFS, &reqbuf);
    if (ret < 0) {
        printf("VIDIOC_REQBUFS failed\n");
        close(fd);
        return -1;
    }

    for (int i = 0; i < reqbuf.count; i++) {
        memset(&buf, 0, sizeof(buf));
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = i;
        ret = ioctl(fd, VIDIOC_QUERYBUF, &buf);
        if (ret < 0) {
            printf("VIDIOC_QUERYBUF failed\n");
            close(fd);
            return -1;
        }

        void *addr = mmap(NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, buf.m.offset);
        if (addr == MAP_FAILED) {
            printf("mmap failed\n");
            close(fd);
            return -1;
        }

        buf.m.userptr = (unsigned long)addr;
        ret = ioctl(fd, VIDIOC_QBUF, &buf);
        if (ret < 0) {
            printf("VIDIOC_QBUF failed\n");
            close(fd);
            return -1;
        }
    }

    enum v4l2_buf_type type;
    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    ret = ioctl(fd, VIDIOC_STREAMON, &type);
    if (ret < 0) {
        printf("VIDIOC_STREAMON failed\n");
        close(fd);
        return -1;
    }

    while (1) {
        memset(&buf, 0, sizeof(buf));
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        ret = ioctl(fd, VIDIOC_DQBUF, &buf);
        if (ret < 0) {
            printf("VIDIOC_DQBUF failed\n");
            close(fd);
            return -1;
        }

        // 这里可以对buf.m.userptr指向的数据进行处理或保存

        ret = ioctl(fd, VIDIOC_QBUF, &buf);
        if (ret < 0) {
            printf("VIDIOC_QBUF failed\n");
            close(fd);
            return -1;
        }
    }

    return 0;
}

这个示例代码中，首先打开摄像头设备文件（CAM_DEV），然后调用VIDIOC_QUERYCAP查询驱动功能，调用VIDIOC_S_FMT设置摄像头采集格式，调用VIDIOC_REQBUFS请求内存，调用mmap将内存映射到用户空间，调用VIDIOC_QBUF将内存缓冲区入队列，最后调用VIDIOC_STREAMON开始采集。然后进入循环，每次采集完成后，调用VIDIOC_DQBUF将内存缓冲区出队列，进行处理或保存，然后调用VIDIOC_QBUF将内存缓冲区再次入队列，继续采集。