USB摄像头驱动框架

写一个USB摄像头驱动程序
1.构造一个usb_driver
2.设置
probe:
2.1. 分配video_device:video_device_alloc
2.2. 设置
.fops
.ioctl_ops (里面需要设置11项)
如果要用内核提供的缓冲区操作函数,还需要构造一个videobuf_queue_ops
2.3. 注册: video_register_device
id_table: 表示支持哪些USB设备
3.注册: usb_register

UVC: USB Video Class
UVC驱动:drivers\media\video\uvc\

uvc_driver.c分析:

  1. usb_register(&uvc_driver.driver);
  2. uvc_probe
    uvc_register_video
    vdev = video_device_alloc();
    vdev->fops = &uvc_fops;
    video_register_device

在www.usb.org下载 uvc specification,
UVC 1.5 Class specification.pdf : 有详细描述
USB_Video_Example 1.5.pdf : 有示例

通过VideoControl Interface来控制,
通过VideoStreaming Interface来读视频数据,
VC里含有多个Unit/Terminal等功能模块,可以通过访问这些模块进行控制,比如调亮度

分析UVC驱动调用过程:
const struct v4l2_file_operations uvc_fops = {
.owner = THIS_MODULE,
.open = uvc_v4l2_open,
.release = uvc_v4l2_release,
.ioctl = uvc_v4l2_ioctl,
.read = uvc_v4l2_read,
.mmap = uvc_v4l2_mmap,
.poll = uvc_v4l2_poll,
};

  1. open:
    uvc_v4l2_open

  2. VIDIOC_QUERYCAP // video->streaming->type 应该是在设备被枚举时分析描述符时设置的
    if (video->streaming->type == V4L2_BUF_TYPE_VIDEO_CAPTURE)
    cap->capabilities = V4L2_CAP_VIDEO_CAPTURE
    | V4L2_CAP_STREAMING;
    else
    cap->capabilities = V4L2_CAP_VIDEO_OUTPUT
    | V4L2_CAP_STREAMING;

  3. VIDIOC_ENUM_FMT // format数组应是在设备被枚举时设置的
    format = &video->streaming->format[fmt->index];

  4. VIDIOC_G_FMT
    uvc_v4l2_get_format // USB摄像头支持多种格式fromat, 每种格式下有多种frame(比如分辨率)
    struct uvc_format *format = video->streaming->cur_format;
    struct uvc_frame *frame = video->streaming->cur_frame;

  5. VIDIOC_TRY_FMT
    uvc_v4l2_try_format
    /* Check if the hardware supports the requested format. /
    /
    Find the closest image size. The distance between image sizes is
    * the size in pixels of the non-overlapping regions between the
    * requested size and the frame-specified size.
    */

  6. VIDIOC_S_FMT // 只是把参数保存起来,还没有发给USB摄像头
    uvc_v4l2_set_format
    uvc_v4l2_try_format
    video->streaming->cur_format = format;
    video->streaming->cur_frame = frame;

  7. VIDIOC_REQBUFS
    uvc_alloc_buffers
    for (; nbuffers > 0; --nbuffers) {
    mem = vmalloc_32(nbuffers * bufsize);
    if (mem != NULL)
    break;
    }

  8. VIDIOC_QUERYBUF
    uvc_query_buffer
    __uvc_query_buffer
    memcpy(v4l2_buf, &buf->buf, sizeof *v4l2_buf); // 复制参数

  9. mmap
    uvc_v4l2_mmap

  10. VIDIOC_QBUF
    uvc_queue_buffer
    list_add_tail(&buf->stream, &queue->mainqueue);
    list_add_tail(&buf->queue, &queue->irqqueue);

  11. VIDIOC_STREAMON
    uvc_video_enable(video, 1) // 把所设置的参数发给硬件,然后启动摄像头
    /* Commit the streaming parameters. /
    uvc_commit_video
    uvc_set_video_ctrl /
    设置格式fromat, frame /
    ret = __uvc_query_ctrl(video->dev /
    哪一个USB设备 /, SET_CUR, 0,
    video->streaming->intfnum /
    哪一个接口: VS /,
    probe ? VS_PROBE_CONTROL : VS_COMMIT_CONTROL, data, size,
    uvc_timeout_param);
    /
    启动:Initialize isochronous/bulk URBs and allocate transfer buffers. */
    uvc_init_video(video, GFP_KERNEL);
    uvc_init_video_isoc / uvc_init_video_bulk
    urb->complete = uvc_video_complete; (收到数据后此函数被调用,它又调用video->decode(urb, video, buf); ==> uvc_video_decode_isoc/uvc_video_encode_bulk => uvc_queue_next_buffer => wake_up(&buf->wait)?

                usb_submit_urb                    	
    
  12. poll
    uvc_v4l2_poll
    uvc_queue_poll
    poll_wait(file, &buf->wait, wait); // 休眠等待有数据

  13. VIDIOC_DQBUF
    uvc_dequeue_buffer
    list_del(&buf->stream);

  14. VIDIOC_STREAMOFF
    uvc_video_enable(video, 0);
    usb_kill_urb(urb);
    usb_free_urb(urb);

分析设置亮度过程:
ioctl: VIDIOC_S_CTRL
uvc_ctrl_set
uvc_ctrl_commit
__uvc_ctrl_commit(video, 0);
uvc_ctrl_commit_entity(video->dev, entity, rollback);
ret = uvc_query_ctrl(dev /* 哪一个USB设备 /, SET_CUR, ctrl->entity->id / 哪一个unit/terminal /,
dev->intfnum /
哪一个接口: VC interface */, ctrl->info->selector,
uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT),
ctrl->info->size);

总结:

  1. UVC设备有2个interface: VideoControl Interface, VideoStreaming Interface

  2. VideoControl Interface用于控制,比如设置亮度。它内部有多个Unit/Terminal(在程序里Unit/Terminal都称为entity)
    可以通过类似的函数来访问:
    ret = uvc_query_ctrl(dev /* 哪一个USB设备 /, SET_CUR, ctrl->entity->id / 哪一个unit/terminal /,
    dev->intfnum /
    哪一个接口: VC interface */, ctrl->info->selector,
    uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT),
    ctrl->info->size);

  3. VideoStreaming Interface用于获得视频数据,也可以用来选择fromat/frame(VS可能有多种format, 一个format支持多种frame, frame用来表示分辨率等信息)
    可以通过类似的函数来访问:
    ret = __uvc_query_ctrl(video->dev /* 哪一个USB设备 /, SET_CUR, 0,
    video->streaming->intfnum /
    哪一个接口: VS */,
    probe ? VS_PROBE_CONTROL : VS_COMMIT_CONTROL, data, size,
    uvc_timeout_param);

  4. 我们在设置FORMAT时只是简单的使用video->streaming->format[fmt->index]等数据,
    这些数据哪来的?
    应是设备被枚举时设置的,也就是分析它的描述符时设置的。

  5. UVC驱动的重点在于:
    描述符的分析
    属性的控制: 通过VideoControl Interface来设置
    格式的选择:通过VideoStreaming Interface来设置
    数据的获得:通过VideoStreaming Interface的URB来获得

USB摄像头驱动框架_第1张图片
两个概念:单元units ,终端terminals

单元:里面的

terminal:用于内外链接。

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