stm32f407vet6+LAN8720A调试以太网遇到软件复位失败问题

我用stm32f407vet6+LAN8720A调试以太网遇到软件复位失败问题，单步调试发现在复位MAC内部寄存器时对以太网总线模式寄存器（ETN_DMABMR）软件复位SR位置1后，硬件未自动清除该位，导致软件，导致代码进入while死循环。

这问题在用官网代码上也复位不成功。代码如下：

/* 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;
}

}

这是我REFCLK引脚的频率图