Altera 10-Gbps Ethernet MAC MegaCore Function - Manual (Page 152)

Chapter 10: Design Considerations 10–3
Sharing Reference Clocks for Multi-Port System Design
February 2014 Altera Corporation 10-Gbps Ethernet MAC MegaCore Function User Guide
10.4. Sharing Reference Clocks for Multi-Port System Design
For multi-port system design, if every port is using the same reference clock source,
the FPLL in every port is merged into a single FPLL. Similarly, the TXPLL for every
channel is merged into a single TXPLL.
If the reference clock source for every port is different, then the merging will not
occur.