General Description: MGTs do not work properly in silicon for the PCS/PMA configuration of the Gigabit Ethernet MAC (GEMAC) core.
The problem is that although the REFCLKSEL input on the MGT does not have an internal inverter on it, it is erroneously considered invertible by the software. This means that whenever the tools select the inverted input, you get the opposite setting of what was intended, and the REFCLK does not drive the MGT properly.
To work around the problem, connect the REFCLK clock to both REFCLK and REFCLK2 ports on the MGT in the gpcs_pma_gen.vhd in the PCS/PMA sublayer, version 1.0. This ensures that no matter which clock the tools select, the correct clock is always provided to the MGT.
This solution has been incorporated into v2.1 of the GEMAC core, and will be fixed in F.21 of the Xilinx implementation tools.