uvc摄像头代码解析3(一)

6.1 重要结构体

6.1.1 uvc数据流

[cpp]

struct uvc_streaming {

struct list_head list; //uvc视频流链表头

struct uvc_device *dev; //uvc设备

struct video_device *vdev; //V4L2视频设备

struct uvc_video_chain *chain; //uvc视频链

atomic_t active;

struct usb_interface *intf; //usb接口设备

int intfnum; //usb接口号

__u16 maxpsize; //最大包尺寸

struct uvc_streaming_header header; //uvc视频流头部

enum v4l2_buf_type type; //V4L2缓冲区类型 输入/输出

unsigned int nformats; //uvc格式个数

struct uvc_format *format; //uvc格式指针

struct uvc_streaming_control ctrl; //uvc数据流控制

struct uvc_format *cur_format; //当前uvc格式指针

struct uvc_frame *cur_frame; //当前uvc帧指针

struct mutex mutex;

unsigned int frozen : 1;

struct uvc_video_queue queue; //uvc视频队列

void (*decode) (struct urb *urb, struct uvc_streaming *video,struct uvc_buffer *buf);//解码函数

struct {

__u8 header[256];

unsigned int header_size;

int skip_payload;

__u32 payload_size;

__u32 max_payload_size;

} bulk;

struct urb *urb[UVC_URBS];//urb数组

char *urb_buffer[UVC_URBS]; //urb缓冲区

dma_addr_t urb_dma[UVC_URBS];//urb DMA缓冲区

unsigned int urb_size;

__u32 sequence;

__u8 last_fid;

};

6.1.2 uvc格式

[cpp]

struct uvc_format { //uvc格式

__u8 type; //类型

__u8 index; //索引

__u8 bpp; //bits per pixel 每像素位数

__u8 colorspace; //颜色空间

__u32 fcc; //压缩格式

__u32 flags; //标记

char name[32]; //名字

unsigned int nframes; //所含uvc帧个数

struct uvc_frame *frame; //uvc帧指针

};

6.1.3 uvc帧

[cpp]

struct uvc_frame { //uvc帧

__u8 bFrameIndex; //帧索引号

__u8 bmCapabilities; //uvc帧兼容性

__u16 wWidth; //宽度

__u16 wHeight; //高度

__u32 dwMinBitRate; //最新位流

__u32 dwMaxBitRate; //最大位流

__u32 dwMaxVideoFrameBufferSize; //最大视频帧缓冲区

__u8 bFrameIntervalType; //间隙类型

__u32 dwDefaultFrameInterval; //默认帧间隙

__u32 *dwFrameInterval; //帧间隙指针

};

6.2 uvc_parse_streaming函数

[cpp]

static int uvc_parse_streaming(struct uvc_device *dev,struct usb_interface *intf)

{

struct uvc_streaming *streaming = NULL; //uvc数据流

struct uvc_format *format; //uvc格式

struct uvc_frame *frame; //uvc帧

struct usb_host_interface *alts = &intf->altsetting[0]; //获取usb接口第一个usb_host_interface (Alt.Setting 0)

unsigned char *_buffer, *buffer = alts->extra; //获取额外描述符

int _buflen, buflen = alts->extralen; //获取额外描述符长度

unsigned int nformats = 0, nframes = 0, nintervals = 0;

unsigned int size, i, n, p;

__u32 *interval;

__u16 psize;

int ret = -EINVAL;

if (intf->cur_altsetting->desc.bInterfaceSubClass != UVC_SC_VIDEOSTREAMING) { //判读usb接口描述符子类是否为视频数据流接口子类

uvc_trace(UVC_TRACE_DESCR, "device %d interface %d isn't a video streaming interface\n", dev->udev->devnum,intf->altsetting[0].desc.bInterfaceNumber);

return -EINVAL;

}

if (usb_driver_claim_interface(&uvc_driver.driver, intf, dev)) { //绑定uvc设备的usb驱动和usb接口

uvc_trace(UVC_TRACE_DESCR, "device %d interface %d is already claimed\n", dev->udev->devnum,intf->altsetting[0].desc.bInterfaceNumber);

retu