While I can largely figure this out from the example schematics. It is not clear from looking at the pinout. From looking at both carrier schematics REFCLK3 seems to belong to HSIO 1 and 3? | REFCLK | HSIO | |-|-| | 0 | 2 | | 1 | 3 | | 2 | 8, 9, 10, 11| | 3 | 3 | | 4 | 6 |