Why does Arria® 10 HPS EMAC RMII interface not work with default 250 MHz EMAC clock?

Description

When selecting RMII interface for Arria® 10 HPS EMAC and using the default 250 MHz clock setting, EMAC will not work normally. You might observe that the TX packet frames fail to send and RX packet frames are received with cyclic redundancy check (CRC) errors.

This is due to RMII interface requires 50 MHz REF_CLK. The default 250 MHz clock is meant for the RGMII interface.

 

Resolution

Select EMAC clock frequency as 50 MHz when choosing the RMII interface as shown in the following figure: