Re: Is Ethernet even possible using the SAME53J ?
The device errata shows that Ethernet was not available on 64-pin devices for silicon rev A, but it has been fixed in rev D. I got confirmation of this from Microchip support. You will have to work with your distributor to make sure you get rev D silicon.
I don't know what pin the GRXDV signal comes out on in the new rev
Hope this helps