If you read DP83825 register 0x15, are you seeing any RX symbol error reported by the PHY? Can you also put DP83825I into the reverse loopback and see if the link partner reports any packet error? The reverse loopback is enabled by setting bit[4] in the BISCR register. The reverse loopback is a special test mode to allow PHY testing with a link partner. In this mode, data that is received from the Link Partner passes through the PHY’s receiver, is looped back at the MAC interface and then transmitted back to the Link Partner. All data signals that come from the MAC are ignored in this mode. If the reverse loopback is working, then this indicates the MDI interface is ok. We may then have to enable the MII loopback to verify the MAC interface.
