V4L2 UVC事件

UVC事件包括两类，分别为数据事件（读写）和异常事件。

数据事件

数据事件对应于select函数的读写事件。
对于UVC Gadget 应用写数据，当事件来到时。应

        struct v4l2_buffer ubuf;
        ret = ioctl(dev->uvc_fd, VIDIOC_DQBUF, &ubuf);
        uvc_video_fill_buffer(dev, &ubuf);//自定义函数，填充数据缓冲区
        ret = ioctl(dev->uvc_fd, VIDIOC_QBUF, &ubuf);

异常事件

异常事件包括UVC本身的控制请求和设备的事件。
首先应先通过VIDIOC_DQEVENT获取事件类型，当然有的事件是需要数据响应返回到UVC Gadget中。

struct v4l2_event {
    __u32                type;
    union {
        struct v4l2_event_vsync        vsync;
        struct v4l2_event_ctrl        ctrl;
        struct v4l2_event_frame_sync    frame_sync;
        struct v4l2_event_src_change    src_change;
        struct v4l2_event_motion_det    motion_det;
        __u8                data[64];
    } u;
    __u32                pending;
    __u32                sequence;
    struct timespec            timestamp;
    __u32                id;
    __u32                reserved[8];
};

struct uvc_request_data {
    __s32 length;
    __u8 data[60];
};

其中type为事件类型

#define UVC_EVENT_FIRST            (V4L2_EVENT_PRIVATE_START + 0)
#define UVC_EVENT_CONNECT        (V4L2_EVENT_PRIVATE_START + 0)
#define UVC_EVENT_DISCONNECT        (V4L2_EVENT_PRIVATE_START + 1)
#define UVC_EVENT_STREAMON        (V4L2_EVENT_PRIVATE_START + 2)
#define UVC_EVENT_STREAMOFF        (V4L2_EVENT_PRIVATE_START + 3)
#define UVC_EVENT_SETUP            (V4L2_EVENT_PRIVATE_START + 4)
#define UVC_EVENT_DATA            (V4L2_EVENT_PRIVATE_START + 5)
#define UVC_EVENT_LAST            (V4L2_EVENT_PRIVATE_START + 5)

当为事件时，v4l2_event.u.data类型为uvc_event

struct uvc_event {
    union {
        enum usb_device_speed speed;
        struct usb_ctrlrequest req;
        struct uvc_request_data data;
    };
};

故

    struct uvc_event *uvc_event = (void *)&v4l2_event.u.data;

uvc_event分为2类：

truct uvc_event {
    union {
        enum usb_device_speed speed;
        struct usb_ctrlrequest req; //UVC_EVENT_SETUP
        struct uvc_request_data data; //UVC_EVENT_DATA
    };
};
struct usb_ctrlrequest {
    __u8 bRequestType;
    __u8 bRequest;
    __le16 wValue;
    __le16 wIndex;
    __le16 wLength;
} __attribute__ ((packed));

struct uvc_request_data {
    __s32 length;
    __u8 data[60];
};