没插网线时，初始化 LwIP总失败，分析后发现是网口初始化总是失败，就是这个函数：HAL_ETH_Init，单步调试了一下，发现没插网线时，DMABMR寄存器的SR位始终为 1，程序卡在等待SR为0后超时退出。这个怎么解决啊？

[mw_shl_code=c,true]/* Ethernet Software reset */
  /* Set the SWR bit: resets all MAC subsystem internal registers and logic */
  /* After reset all the registers holds their respective reset values */
  (heth->Instance)->DMABMR |= ETH_DMABMR_SR;
  
  /* Get tick */
  tickstart = HAL_GetTick();
  
  /* Wait for software reset */
  while (((heth->Instance)->DMABMR & ETH_DMABMR_SR) != (uint32_t)RESET)
  {
    /* Check for the Timeout */
    if((HAL_GetTick() - tickstart ) > ETH_TIMEOUT_SWRESET)
    {     
      heth->State= HAL_ETH_STATE_TIMEOUT;
  
      /* Process Unlocked */
      __HAL_UNLOCK(heth);
   
      /* Note: The SWR is not performed if the ETH_RX_CLK or the ETH_TX_CLK are  
         not available, please check your external PHY or the IO configuration */
      return HAL_TIMEOUT;
    }
  }[/mw_shl_code]