UVC: USB Video Class
UVC驅動：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下載 uvc specification,
UVC 1.5 Class specification.pdf : 有詳細描述
USB_Video_Example 1.5.pdf : 有示例
通過VideoControl Interface來控制，
通過VideoStreaming Interface來讀視頻數據，
VC里含有多個Unit/Terminal等功能模塊，可以通過訪問這些模塊進行控制，比如調亮度
分析UVC驅動調用過程：
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 應該是在設備被枚舉時分析描述符時設置的
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數組應是在設備被枚舉時設置的
format = &video->streaming->format[fmt->index];
4. VIDIOC_G_FMT
uvc_v4l2_get_format // USB攝像頭支持多種格式fromat, 每種格式下有多種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 // 只是把參數保存起來，還沒有發給USB攝像頭
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); // 復制參數
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) // 把所設置的參數發給硬件,然后啟動攝像頭
/* Commit the streaming parameters. */
uvc_commit_video
uvc_set_video_ctrl /* 設置格式fromat, frame */
ret = __uvc_query_ctrl(video->dev /* 哪一個USB設備 */, SET_CUR, 0,
video->streaming->intfnum /* 哪一個接口: VS */,
probe ? VS_PROBE_CONTROL : VS_COMMIT_CONTROL, data, size,
uvc_timeout_param);
/* 啟動：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; (收到數據后此函數被調用,它又調用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); // 休眠等待有數據
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);
分析設置亮度過程：
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 /* 哪一個USB設備 */, SET_CUR, ctrl->entity->id /* 哪一個unit/terminal */,
dev->intfnum /* 哪一個接口: VC interface */, ctrl->info->selector,
uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT),
ctrl->info->size);
總結：
1. UVC設備有2個interface: VideoControl Interface, VideoStreaming Interface
2. VideoControl Interface用於控制，比如設置亮度。它內部有多個Unit/Terminal(在程序里Unit/Terminal都稱為entity)
可以通過類似的函數來訪問：
ret = uvc_query_ctrl(dev /* 哪一個USB設備 */, SET_CUR, ctrl->entity->id /* 哪一個unit/terminal */,
dev->intfnum /* 哪一個接口: VC interface */, ctrl->info->selector,
uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT),
ctrl->info->size);
3. VideoStreaming Interface用於獲得視頻數據，也可以用來選擇fromat/frame(VS可能有多種format, 一個format支持多種frame， frame用來表示分辨率等信息)
可以通過類似的函數來訪問：
ret = __uvc_query_ctrl(video->dev /* 哪一個USB設備 */, SET_CUR, 0,
video->streaming->intfnum /* 哪一個接口: VS */,
probe ? VS_PROBE_CONTROL : VS_COMMIT_CONTROL, data, size,
uvc_timeout_param);
4. 我們在設置FORMAT時只是簡單的使用video->streaming->format[fmt->index]等數據，
這些數據哪來的？
應是設備被枚舉時設置的，也就是分析它的描述符時設置的。
5. UVC驅動的重點在於：
描述符的分析
屬性的控制: 通過VideoControl Interface來設置
格式的選擇：通過VideoStreaming Interface來設置
數據的獲得：通過VideoStreaming Interface的URB來獲得
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