uvc摄像头代码解析3

6.uvc解析uvc视频流

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);  

        return -EINVAL;  

    }  

    streaming = kzalloc(sizeof *streaming, GFP_KERNEL); //分配uvc数据流内存  

    if (streaming == NULL) {  

        usb_driver_release_interface(&uvc_driver.driver, intf);  

        return -EINVAL;  

    }  

    mutex_init(&streaming->mutex);  

    streaming->dev = dev;    //uvc数据流和uvc设备捆绑  

    streaming->intf = usb_get_intf(intf);    //uvc数据流和usb接口捆绑,并增加引用计数  

    streaming->intfnum = intf->cur_altsetting->desc.bInterfaceNumber;  //设置接口号  

    /* The Pico iMage webcam has its class-specific interface descriptors after the endpoint descriptors. */  

    if (buflen == 0) {  //Pico iMage webcam 特殊处理  

        for (i = 0; i < alts->desc.bNumEndpoints; ++i) {  

            struct usb_host_endpoint *ep = &alts->endpoint[i];  

            if (ep->extralen == 0)  

                continue;  

            if (ep->extralen > 2 && ep->extra[1] == USB_DT_CS_INTERFACE) {  

                uvc_trace(UVC_TRACE_DESCR, "trying extra data from endpoint %u.\n", i);  

                buffer = alts->endpoint[i].extra;  

                buflen = alts->endpoint[i].extralen;  

                break;  

            }  

        }  

    }  

    /* Skip the standard interface descriptors. 跳过标准的接口描述符*/  

    while (buflen > 2 && buffer[1] != USB_DT_CS_INTERFACE) {   

        buflen -= buffer[0];  

        buffer += buffer[0];  

    }  

    if (buflen <= 2) {  

        uvc_trace(UVC_TRACE_DESCR, "no class-specific streaming interface descriptors found.\n");  

        goto error;  

    }  

    /* Parse the header descriptor. 解析header描述符*/   //Class-specific VS Interface Input Header Descriptor  

    switch (buffer[2]) {    //bDescriptorSubtype  

    case UVC_VS_OUTPUT_HEADER:  //输出类型的视频流  

        streaming->type = V4L2_BUF_TYPE_VIDEO_OUTPUT;    //设置为V4L2视频buf输出  

        size = 9;  

        break;  

    case UVC_VS_INPUT_HEADER:   //输入类型的视频流  

        streaming->type = V4L2_BUF_TYPE_VIDEO_CAPTURE;   //设置为V4L2视频buf输入  

        size = 13;  

        break;  

    default:  

        uvc_trace(UVC_TRACE_DESCR, "device %d videostreaming interface %d HEADER descriptor not found.\n", dev->udev->devnum,alts->desc.bInterfaceNumber);  

        goto error;  

    }  

    p = buflen >= 4 ? buffer[3] : 0; //bNumFormats uvc格式format个数  

    n = buflen >= size ? buffer[size-1] : 0; //bControlSize 控制位域大小  

    if (buflen < size + p*n) {       //检测buflen长度是否合适  

        uvc_trace(UVC_TRACE_DESCR, "device %d videostreaming interface %d HEADER descriptor is invalid.\n",dev->udev->devnum, alts->desc.bInterfaceNumber);  

        goto error;  

    }  

    //初始化uvc视频流头部  

    streaming->header.bNumFormats = p;   //uvc格式format格式个数  

    streaming->header.bEndpointAddress = buffer[6];  //端点地址  

    if (buffer[2] == UVC_VS_INPUT_HEADER) { //输入的视频流  

        streaming->header.bmInfo = buffer[7];            //信息位图(兼容性)  

        streaming->header.bTerminalLink = buffer[8]; //连接到的输出Terminal ID号  

        streaming->header.bStillCaptureMethod = buffer[9];   //静态图像捕捉方法(Method 1、Method 2、Method 3)  

        streaming->header.bTriggerSupport = buffer[10];  //硬件触发支持  

        streaming->header.bTriggerUsage = buffer[11];    //触发用例  

    }   

    else {  

        streaming->header.bTerminalLink = buffer[7]; //连接到的输入Terminal ID号  

    }  

    streaming->header.bControlSize = n;  //控制位域大小  

    streaming->header.bmaControls = kmemdup(&buffer[size], p * n,GFP_KERNEL);    //初始化bmaControls(x)位图(大小=帧数*位域大小)  

    if (streaming->header.bmaControls == NULL) {  

        ret = -ENOMEM;  

        goto error;  

    }  

    buflen -= buffer[0];  

    buffer += buffer[0];    //指向下一个描述符  

    _buffer = buffer;  

    _buflen = buflen;   //指向同一个描述符  

解析完vs header后解析剩下的vs描述符

第一次解析描述符 统计uvc帧、uvc格式、间隔,并分配内存

[cpp]  

/* Count the format and frame descriptors. 计算格式描述符和帧描述符个数*/  

    while (_buflen > 2 && _buffer[1] == USB_DT_CS_INTERFACE) {  

        switch (_buffer[2]) {  

        case UVC_VS_FORMAT_UNCOMPRESSED:  

        case UVC_VS_FORMAT_MJPEG:  

        case UVC_VS_FORMAT_FRAME_BASED:  

            nformats++;  

            break;  

        case UVC_VS_FORMAT_DV:  

            /* DV format has no frame descriptor. We will create a dummy frame descriptor with a dummy frame interval. */  

            nformats++;  

            nframes++;  

            nintervals++;  

            break;  

        case UVC_VS_FORMAT_MPEG2TS:  

        case UVC_VS_FORMAT_STREAM_BASED:  

            uvc_trace(UVC_TRACE_DESCR, "device %d videostreaming interface %d FORMAT %u is not supported.\n",dev->udev->devnum,alts->desc.bInterfaceNumber, _buffer[2]);  

            break;  

        case UVC_VS_FRAME_UNCOMPRESSED:  

        case UVC_VS_FRAME_MJPEG:  

            nframes++;  

            if (_buflen > 25)  

                nintervals += _buffer[25] ? _buffer[25] : 3;  

            break;  

        case UVC_VS_FRAME_FRAME_BASED:  

            nframes++;  

            if (_buflen > 21)  

                nintervals += _buffer[21] ? _buffer[21] : 3;  

            break;  

        }   //计算uvc帧和uvc格式的个数及间隔个数  

        _buflen -= _buffer[0];    

        _buffer += _buffer[0];  //跳到下一个描述符  

    }  

    if (nformats == 0) {  

        uvc_trace(UVC_TRACE_DESCR, "device %d videostreaming interface %d has no supported formats defined.\n",dev->udev->devnum, alts->desc.bInterfaceNumber);  

        goto error;  

    }  

    //    uvc格式数 * uvc格式大小    + uvc帧   * uvc帧大小    + 间隔数     * 间隔大小  

    size = nformats * sizeof *format + nframes * sizeof *frame+ nintervals * sizeof *interval;  

    format = kzalloc(size, GFP_KERNEL); //分配uvc格式和uvc帧的内存  

    if (format == NULL) {  

        ret = -ENOMEM;  

        goto error;  

    }  

    frame = (struct uvc_frame *)&format[nformats];  //uvc帧存放在uvc格式数组后面  

    interval = (__u32 *)&frame[nframes];    //间隔放在帧后面  

    streaming->format = format;  //uvc视频流捆绑uvc格式结构体  

    streaming->nformats = nformats;  //uvc格式个数  

第二次解析描述符

[cpp]  

/* Parse the format descriptors.解析格式描述符 */  

while (buflen > 2 && buffer[1] == USB_DT_CS_INTERFACE) {  

    switch (buffer[2]) {    //bDescriptorSubtype描述符类型  

    case UVC_VS_FORMAT_UNCOMPRESSED:  

    case UVC_VS_FORMAT_MJPEG:  

    case UVC_VS_FORMAT_DV:  

    case UVC_VS_FORMAT_FRAME_BASED:  

        format->frame = frame;   //uvc格式的帧指针 指向uvc帧地址  

        ret = uvc_parse_format(dev, streaming, format,&interval, buffer, buflen);   //7.解析uvc格式描述符  

        if (ret < 0)  

            goto error;  

        frame += format->nframes;    //uvc帧地址指向下一个uvc格式所属的uvc帧地址  

        format++;   //指向下一个uvc格式  

        buflen -= ret;    

        buffer += ret;  //指向下一个uvc格式描述符  

        continue;