Why does the Intel® Arria® 10 HPS EMAC in RMII mode is not able to send out Ethernet packets?

Due to a problem in the Intel® Arria® 10 SoC device, there are chances that you may observe the HPS EMAC in RMII mode producing double data rate. This phenomenon may be due to board setup or layout issue.  The actual root cause is unidentified.

To work around this problem, you can implement a soft logic IP converter for MII to RMII by routing EMAC IO to FPGA fabric through HPS shared IO. These RMII signal pins are then routed back to the same EMAC signal pins. Be aware that this workaround consumes a large amount of HPS pins.

Intel recommends the user implement RGMII mode which is the preferred EMAC interface with proven functionality and higher bandwidth.