uvc摄像头代码解析4

7.uvc_parse_format

7.1 uvc格式描述符

struct uvc_format_desc { //uvc格式描述符
char *name; //uvc格式描述符名字
__u8 guid[16];//全局唯一ID
__u32 fcc; //压缩格式
};

7.2 uvc解析1个格式描述符

static int uvc_parse_format(struct uvc_device *dev,struct uvc_streaming *streaming, struct uvc_format *format,__u32 **intervals, unsigned char *buffer, int buflen)
{
	struct usb_interface *intf = streaming->intf;	//获取usb接口
	struct usb_host_interface *alts = intf->cur_altsetting;	//获取usb_host_interface
	struct uvc_format_desc *fmtdesc;	//uvc格式描述符
	struct uvc_frame *frame;	//uvc帧
	const unsigned char *start = buffer;
	unsigned int interval;
	unsigned int i, n;
	__u8 ftype;

	format->type = buffer[2];	//uvc格式类型
	format->index = buffer[3];	//uvc格式索引
	switch (buffer[2]) {	//uvc格式类型
	case UVC_VS_FORMAT_UNCOMPRESSED:

case UVC_VS_FORMAT_FRAME_BASED:

		n = buffer[2] == UVC_VS_FORMAT_UNCOMPRESSED ? 27 : 28;	//获取描述符大小
		if (buflen < n) {	//检验buflen大小
			uvc_trace(UVC_TRACE_DESCR, "device %d videostreaming interface %d FORMAT error\n",dev->udev->devnum,alts->desc.bInterfaceNumber);
			return -EINVAL;
		}
		/* Find the format descriptor from its GUID. */
		fmtdesc = uvc_format_by_guid(&buffer[5]);	//获取uvc格式描述符
		if (fmtdesc != NULL) {	//设置uvc格式编码格式名字
			strlcpy(format->name, fmtdesc->name,sizeof format->name);
			format->fcc = fmtdesc->fcc;	//设置uvc格式的fcc(压缩格式)
		} 
		else {	//不能识别的格式
			uvc_printk(KERN_INFO, "Unknown video format %pUl\n",&buffer[5]);
			snprintf(format->name, sizeof(format->name), "%pUl\n",&buffer[5]);
			format->fcc = 0;
		}
		format->bpp = buffer[21];	//设置uvc格式bpp(每像素多少位)
		if (buffer[2] == UVC_VS_FORMAT_UNCOMPRESSED) {
			ftype = UVC_VS_FRAME_UNCOMPRESSED;	//设置ftype(frame type)
		} 
　　else {
			ftype = UVC_VS_FRAME_FRAME_BASED;	//设置ftype(frame type)
			if (buffer[27])
				format->flags = UVC_FMT_FLAG_COMPRESSED;	//设置uvc格式标志(压缩的)
		}
		break;
	case UVC_VS_FORMAT_MJPEG:

		if (buflen < 11) {	//检验buflen大小
			uvc_trace(UVC_TRACE_DESCR, "device %d videostreaming interface %d FORMAT error\n",dev->udev->devnum,alts->desc.bInterfaceNumber);
			return -EINVAL;
		}
		strlcpy(format->name, "MJPEG", sizeof format->name);	//设置uvc格式编码格式名字“MJPEG”
		format->fcc = V4L2_PIX_FMT_MJPEG;	//设置uvc格式的fcc(压缩格式)
		format->flags = UVC_FMT_FLAG_COMPRESSED;	//设置uvc格式标志(压缩的)
		format->bpp = 0;	//设置uvc格式bpp(每像素多少位)
		ftype = UVC_VS_FRAME_MJPEG;	//设置ftype(frame type)
		break;
	case UVC_VS_FORMAT_DV:

		if (buflen < 9) {	//检验buflen大小
			uvc_trace(UVC_TRACE_DESCR, "device %d videostreaming interface %d FORMAT error\n",dev->udev->devnum,alts->desc.bInterfaceNumber);
			return -EINVAL;
		}
		switch (buffer[8] & 0x7f) {	//bFormatType格式类型
		case 0:	//设置uvc格式编码格式名字 "SD-DV"
			strlcpy(format->name, "SD-DV", sizeof format->name);
			break;
		case 1:	//设置uvc格式编码格式名字 "SDL-DV"
			strlcpy(format->name, "SDL-DV", sizeof format->name);
			break;
		case 2:	//设置uvc格式编码格式名字 "HD-DV"
			strlcpy(format->name, "HD-DV", sizeof format->name);
			break;
		default:
			uvc_trace(UVC_TRACE_DESCR, "device %d videostreaming interface %d: unknown DV format %u\n",dev->udev->devnum,alts->desc.bInterfaceNumber, buffer[8]);
			return -EINVAL;
		}
		strlcat(format->name, buffer[8] & (1 << 7) ? " 60Hz" : " 50Hz",sizeof format->name);	//扫描格式eg("HD-DV 60Hz")
		format->fcc = V4L2_PIX_FMT_DV;	//设置uvc格式的fcc(压缩格式)
		format->flags = UVC_FMT_FLAG_COMPRESSED | UVC_FMT_FLAG_STREAM;	//设置uvc格式标志(压缩的|数据流)
		format->bpp = 0;	//设置uvc格式bpp(每像素多少位)
		ftype = 0;	//设置ftype(frame type)
		/* Create a dummy frame descriptor. 创建插入一个帧描述符*/
		frame = &format->frame[0];	//获取uvc格式的第一个帧地址
		memset(&format->frame[0], 0, sizeof format->frame[0]);	//初始化uvc帧
		frame->bFrameIntervalType = 1;	//uvc帧间隔类型
		frame->dwDefaultFrameInterval = 1;	//uvc帧默认间隔
		frame->dwFrameInterval = *intervals;	//uvc帧间隔
		*(*intervals)++ = 1;	//添加间隔
		format->nframes = 1;	//uvc格式的帧个数设置为1
		break;
	case UVC_VS_FORMAT_MPEG2TS:
	case UVC_VS_FORMAT_STREAM_BASED:
		/* Not supported yet. */
	default:
		uvc_trace(UVC_TRACE_DESCR, "device %d videostreaming interface %d unsupported format %u\n",dev->udev->devnum, alts->desc.bInterfaceNumber,buffer[2]);
		return -EINVAL;
	}
	uvc_trace(UVC_TRACE_DESCR, "Found format %s.\n", format->name);
	buflen -= buffer[0];
	buffer += buffer[0];	//下一个描述符(uvc帧描述符)
	/* Parse the frame descriptors. Only uncompressed, MJPEG and frame based formats have frame descriptors.*/
	while (buflen > 2 && buffer[1] == USB_DT_CS_INTERFACE && buffer[2] == ftype) {	//buffer[2]=bDescriptorSubtype==frame type?
		frame = &format->frame[format->nframes];	//获取第二个uvc格式的uvc帧指针
//UVC_VS_FRAME_FRAME_BASED参看USB_Video_Payload_Frame_Based_1.5.pdf  P15
		if (ftype != UVC_VS_FRAME_FRAME_BASED)	//获取支持的不连续帧间隔数/连续帧间隔
			n = buflen > 25 ? buffer[25] : 0;
		else
			n = buflen > 21 ? buffer[21] : 0;	
		n = n ? n : 3;	//支持不连续帧间隔？支持不连续帧间隔间隔数:连续帧间隔
		if (buflen < 26 + 4*n) {	//检验buflen大小
			uvc_trace(UVC_TRACE_DESCR, "device %d videostreaming interface %d FRAME error\n", dev->udev->devnum,alts->desc.bInterfaceNumber);
			return -EINVAL;
		}
		frame->bFrameIndex = buffer[3];	//获取uvc帧索引
		frame->bmCapabilities = buffer[4];	//获取uvc帧兼容性
		frame->wWidth = get_unaligned_le16(&buffer[5]);	//解码uvc视频宽度
		frame->wHeight = get_unaligned_le16(&buffer[7]);	//解码uvc视频高度
		frame->dwMinBitRate = get_unaligned_le32(&buffer[9]);	//解码uvc视频最小位流
		frame->dwMaxBitRate = get_unaligned_le32(&buffer[13]);	//解码uvc视频最大位流
		if (ftype != UVC_VS_FRAME_FRAME_BASED) {
			frame->dwMaxVideoFrameBufferSize =get_unaligned_le32(&buffer[17]);	//uvc最大视频帧缓冲区大小
			frame->dwDefaultFrameInterval =get_unaligned_le32(&buffer[21]);	//uvc默认帧间隔
			frame->bFrameIntervalType = buffer[25];	//uvc帧间隔类型
		} 
		else {
			frame->dwMaxVideoFrameBufferSize = 0;	//uvc最大视频帧缓冲区大小
			frame->dwDefaultFrameInterval =get_unaligned_le32(&buffer[17]);	//uvc默认帧间隔
			frame->bFrameIntervalType = buffer[21];	//uvc帧间隔类型
		}
		frame->dwFrameInterval = *intervals;	//设置uvc帧间隔指针
		if (!(format->flags & UVC_FMT_FLAG_COMPRESSED))	//uvc格式标志(压缩的)
			frame->dwMaxVideoFrameBufferSize = format->bpp * frame->wWidth * frame->wHeight / 8;	//计算uvc帧最大视频格式缓冲去大小(byte)
		for (i = 0; i < n; ++i) {
			interval = get_unaligned_le32(&buffer[26+4*i]);	//获取uvc帧间隔
			*(*intervals)++ = interval ? interval : 1;	//调整uvc帧间隔大小
		}
		/* Make sure that the default frame interval stays between the boundaries.*/
		n -= frame->bFrameIntervalType ? 1 : 2;	//uvc帧间隔边界调整
		frame->dwDefaultFrameInterval = min(frame->dwFrameInterval[n], max(frame->dwFrameInterval[0],frame->dwDefaultFrameInterval));
		if (dev->quirks & UVC_QUIRK_RESTRICT_FRAME_RATE) {
			frame->bFrameIntervalType = 1;
			frame->dwFrameInterval[0] = frame->dwDefaultFrameInterval;
		}
		uvc_trace(UVC_TRACE_DESCR, "- %ux%u (%u.%u fps)\n",frame->wWidth, frame->wHeight,10000000/frame->dwDefaultFrameInterval,(100000000/frame->dwDefaultFrameInterval)%10);
		format->nframes++;	//调整uvc格式帧数
		buflen -= buffer[0];
		buffer += buffer[0];	//指向下一个描述符(uvc帧描述符)
	}
	if (buflen > 2 && buffer[1] == USB_DT_CS_INTERFACE && buffer[2] == UVC_VS_STILL_IMAGE_FRAME) {	//静态图像帧
		buflen -= buffer[0];
		buffer += buffer[0];	//跳过指向下一个描述符
	}
	if (buflen > 2 && buffer[1] == USB_DT_CS_INTERFACE && buffer[2] == UVC_VS_COLORFORMAT) { //颜色格式帧
		if (buflen < 6) {
			uvc_trace(UVC_TRACE_DESCR, "device %d videostreaming interface %d COLORFORMAT error\n",dev->udev->devnum,alts->desc.bInterfaceNumber);
			return -EINVAL;
		}
		format->colorspace = uvc_colorspace(buffer[3]);	//buffer[3]=bColorPrimaries 设置颜色空间
		buflen -= buffer[0];
		buffer += buffer[0];	//指向下一描述符
	}
	return buffer - start;	//返回解析了的uvc格式描述符+所含的uvc帧描述符长度
}

7.3 设置颜色空间

static __u32 uvc_colorspace(const __u8 primaries)
{
	static const __u8 colorprimaries[] = {
		0,
		V4L2_COLORSPACE_SRGB,
		V4L2_COLORSPACE_470_SYSTEM_M,
		V4L2_COLORSPACE_470_SYSTEM_BG,
		V4L2_COLORSPACE_SMPTE170M,
		V4L2_COLORSPACE_SMPTE240M,
	};
	if (primaries < ARRAY_SIZE(colorprimaries))
		return colorprimaries[primaries];	//返回颜色空间数组项
	return 0;
}

7.4 uvc格式/uvc帧/uvc视频流