Because both mii_tx_clk and mii_rx_clk are sourced by the external
PHY device connected to the MII, it is not possible to share transmitter or receiver clock
resources across multiple instantiations of the core. Each instance of the core requires its
own independent clocking resources. Therefore, the logic of the following figure must be
duplicated for each instance of the core.
Figure 1. MII Transceiver, Receiver and Clock Logic for UltraScale Devices
