About problem with using EMAC splitter and GMII_TO_RGMII

I am newer.

One of EMAC in HPS is being used by the construction with the pin of FPGA.
The design of the hardware is reference of the following site.

Now, Hardware guy is gone.

When I tried to do ping test by using WindowsPC, I confirmed it worked fine in 10Mbps(Full/Half), 1000Mbps.

But It failed only at 100Mbs.

So I have investigated now, and I did following procedure,

  • Set the ctrl register of System Manager(0xFFD08060) to “1” (RGMII).

It works fine. It passes ping test at 10Mbps, 100Mbps and 1000Mbps.

But I do not understand why?
I think that EMAC may be connected to GMII_TO_RGMII IP package.
So the value of ctrl register of System Manager(0xFFD08060) shall be “0”(GMII).
Please tell me why.

Best Regards,