USBD_DataInStage

static uint8_t USBD_DataInStage(USB_OTG_CORE_HANDLE *pdev , uint8_t epnum)
{
  USB_OTG_EP *ep;
  //端点0
  if(epnum == 0) 
  {
    ep = &pdev->dev.in_ep[0];
    //端点0处于向主机发送数据阶段
    if ( pdev->dev.device_state == USB_OTG_EP0_DATA_IN)
    {
      if(ep->rem_data_len > ep->maxpacket)//未发完完成
      {
        ep->rem_data_len -=  ep->maxpacket;
        if(pdev->cfg.dma_enable == 1)
        {
          /* in slave mode this, is handled by the TxFifoEmpty ISR */
          ep->xfer_buff += ep->maxpacket;
        }
        USBD_CtlContinueSendData (pdev,ep->xfer_buff,ep->rem_data_len);//继续发送
      }
      else
      { /* last packet is MPS multiple, so send ZLP packet */
        if((ep->total_data_len % ep->maxpacket == 0) &&(ep->total_data_len >= ep->maxpacket) &&(ep->total_data_len < ep->ctl_data_len ))
        {
        //发送0数据包，告诉主机发送完了
        //1.total_data_len % maxpacket == 0 实际数据长度刚好是 maxpacket 的整数倍
        //2.total_data_len >= maxpacket 实际数据至少有 1 个满包
        //3.otal_data_len < ctl_data_len 实际数据少于主机请求的数量(这是最关键的条件:主机期待的数据比设备实际有的多，设备需要"提前终止"传输)
          USBD_CtlContinueSendData(pdev , NULL, 0);
          ep->ctl_data_len = 0;
        }
        else
        {
          if((pdev->dev.class_cb->EP0_TxSent != NULL)&&(pdev->dev.device_status == USB_OTG_CONFIGURED))
          {
            pdev->dev.class_cb->EP0_TxSent(pdev); 
          }
          USBD_CtlReceiveStatus(pdev);//等待接收状态
        }
      }
    }
    if (pdev->dev.test_mode == 1)
    {
      USBD_RunTestMode(pdev); 
      pdev->dev.test_mode = 0;
    }
  }
  //其它端点，调用类回调
  else if((pdev->dev.class_cb->DataIn != NULL)&& (pdev->dev.device_status == USB_OTG_CONFIGURED))
  {
    pdev->dev.class_cb->DataIn(pdev, epnum); 
  }  
  return USBD_OK;
}