Altera Triple Speed Ethernet with DP83848 ethernet board on a Cyclone V GX starter kit

Hie, The Triple Speed Ethernet does not support RMII. As you are aware it only support RGMII, MII and others. The converter card is not Intel's recommended method as we have not validated it in-house. Hence, this is out of specs use case. Hence, I cannot guarantee this will work. However, I will try to guide you by providing some guidelines on the next debug steps. It seems you have done the first level due diligence by checking if the Physical connections and Phy clocks can be detected and it seems to be detected. What I recommend next is; you could try to access each Phy device by writing the Phy address to the MDIO registers. Ensure the AVMM is accessing the MDIO registers correctly. Please refer to section 4.1.12 and subsequent sections of user guide: https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/ug/ug_ethernet.pdf Regards, Nathan