STM32F767+DP83848K速度到不了100M的原因？

工作在100Mbps的条件下，TX_CLK,RX_CLK引脚均为25Mhz。速率自协商，程序返回速率标志只有10M,请帮忙分析一下可能的原因？谢谢！

if((phyreg PHY_SPEED_STATUS) == PHY_SPEED_STATUS)
{
/* Set Ethernet speed to 10M following the auto-negotiation */
(heth->Init).Speed = ETH_SPEED_10M;
}
else
{

   /* Set Ethernet speed to 100M following the auto-negotiation */
   (heth->Init).Speed = ETH_SPEED_100M;
}

上述返回(heth->Init).Speed = ETH_SPEED_10M