6.uvc解析uvc視頻流
6.1 重要結構體
6.1.1 uvc數據流
[cpp]
struct uvc_streaming {
struct list_head list; //uvc視頻流鏈表頭
struct uvc_device *dev; //uvc設備
struct video_device *vdev; //V4L2視頻設備
struct uvc_video_chain *chain; //uvc視頻鏈
atomic_t active;
struct usb_interface *intf; //usb接口設備
int intfnum; //usb接口號
__u16 maxpsize; //最大包尺寸
struct uvc_streaming_header header; //uvc視頻流頭部
enum v4l2_buf_type type; //V4L2緩沖區類型 輸入/輸出
unsigned int nformats; //uvc格式個數
struct uvc_format *format; //uvc格式指針
struct uvc_streaming_control ctrl; //uvc數據流控制
struct uvc_format *cur_format; //當前uvc格式指針
struct uvc_frame *cur_frame; //當前uvc幀指針
struct mutex mutex;
unsigned int frozen : 1;
struct uvc_video_queue queue; //uvc視頻隊列
void (*decode) (struct urb *urb, struct uvc_streaming *video,struct uvc_buffer *buf);//解碼函數
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數組
char *urb_buffer[UVC_URBS]; //urb緩沖區
dma_addr_t urb_dma[UVC_URBS];//urb DMA緩沖區
unsigned int urb_size;
__u32 sequence;
__u8 last_fid;
};
6.1.2 uvc格式
[cpp]
struct uvc_format { //uvc格式
__u8 type; //類型
__u8 index; //索引
__u8 bpp; //bits per pixel 每像素位數
__u8 colorspace; //顏色空間
__u32 fcc; //壓縮格式
__u32 flags; //標記
char name[32]; //名字
unsigned int nframes; //所含uvc幀個數
struct uvc_frame *frame; //uvc幀指針
};
6.1.3 uvc幀
[cpp]
struct uvc_frame { //uvc幀
__u8 bFrameIndex; //幀索引號
__u8 bmCapabilities; //uvc幀兼容性
__u16 wWidth; //寬度
__u16 wHeight; //高度
__u32 dwMinBitRate; //最新位流
__u32 dwMaxBitRate; //最大位流
__u32 dwMaxVideoFrameBufferSize; //最大視頻幀緩沖區
__u8 bFrameIntervalType; //間隙類型
__u32 dwDefaultFrameInterval; //默認幀間隙
__u32 *dwFrameInterval; //幀間隙指針
};
6.2 uvc_parse_streaming函數
[cpp]
static int uvc_parse_streaming(struct uvc_device *dev,struct usb_interface *intf)
{
struct uvc_streaming *streaming = NULL; //uvc數據流
struct uvc_format *format; //uvc格式
struct uvc_frame *frame; //uvc幀
struct usb_host_interface *alts = &intf->altsetting[0]; //獲取usb接口第一個usb_host_interface (Alt.Setting 0)
unsigned char *_buffer, *buffer = alts->extra; //獲取額外描述符
int _buflen, buflen = alts->extralen; //獲取額外描述符長度
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) { //判讀usb接口描述符子類是否為視頻數據流接口子類
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)) { //綁定uvc設備的usb驅動和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數據流內存
if (streaming == NULL) {
usb_driver_release_interface(&uvc_driver.driver, intf);
return -EINVAL;
}
mutex_init(&streaming->mutex);
streaming->dev = dev; //uvc數據流和uvc設備捆綁
streaming->intf = usb_get_intf(intf); //uvc數據流和usb接口捆綁,並增加引用計數
streaming->intfnum = intf->cur_altsetting->desc.bInterfaceNumber; //設置接口號
/* The Pico iMage webcam has its class-specific interface descriptors after the endpoint descriptors. */
if (buflen == 0) { //Pico iMage webcam 特殊處理
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. 跳過標准的接口描述符*/
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: //輸出類型的視頻流
streaming->type = V4L2_BUF_TYPE_VIDEO_OUTPUT; //設置為V4L2視頻buf輸出
size = 9;
break;
case UVC_VS_INPUT_HEADER: //輸入類型的視頻流
streaming->type = V4L2_BUF_TYPE_VIDEO_CAPTURE; //設置為V4L2視頻buf輸入
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個數
n = buflen >= size ? buffer[size-1] : 0; //bControlSize 控制位域大小
if (buflen < size + p*n) { //檢測buflen長度是否合適
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視頻流頭部
streaming->header.bNumFormats = p; //uvc格式format格式個數
streaming->header.bEndpointAddress = buffer[6]; //端點地址
if (buffer[2] == UVC_VS_INPUT_HEADER) { //輸入的視頻流
streaming->header.bmInfo = buffer[7]; //信息位圖(兼容性)
streaming->header.bTerminalLink = buffer[8]; //連接到的輸出Terminal ID號
streaming->header.bStillCaptureMethod = buffer[9]; //靜態圖像捕捉方法(Method 1、Method 2、Method 3)
streaming->header.bTriggerSupport = buffer[10]; //硬件觸發支持
streaming->header.bTriggerUsage = buffer[11]; //觸發用例
}
else {
streaming->header.bTerminalLink = buffer[7]; //連接到的輸入Terminal ID號
}
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)位圖(大小=幀數*位域大小)
if (streaming->header.bmaControls == NULL) {
ret = -ENOMEM;
goto error;
}
buflen -= buffer[0];
buffer += buffer[0]; //指向下一個描述符
_buffer = buffer;
_buflen = buflen; //指向同一個描述符
解析完vs header後解析剩下的vs描述符
第一次解析描述符 統計uvc幀、uvc格式、間隔,並分配內存
[cpp]
/* Count the format and frame descriptors. 計算格式描述符和幀描述符個數*/
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;
} //計算uvc幀和uvc格式的個數及間隔個數
_buflen -= _buffer[0];
_buffer += _buffer[0]; //跳到下一個描述符
}
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格式數 * uvc格式大小 + uvc幀 * uvc幀大小 + 間隔數 * 間隔大小
size = nformats * sizeof *format + nframes * sizeof *frame+ nintervals * sizeof *interval;
format = kzalloc(size, GFP_KERNEL); //分配uvc格式和uvc幀的內存
if (format == NULL) {
ret = -ENOMEM;
goto error;
}
frame = (struct uvc_frame *)&format[nformats]; //uvc幀存放在uvc格式數組後面
interval = (__u32 *)&frame[nframes]; //間隔放在幀後面
streaming->format = format; //uvc視頻流捆綁uvc格式結構體
streaming->nformats = nformats; //uvc格式個數
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描述符類型
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格式的幀指針 指向uvc幀地址
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幀地址指向下一個uvc格式所屬的uvc幀地址
format++; //指向下一個uvc格式
buflen -= ret;
buffer += ret; //指向下一個uvc格式描述符
continue;
