RGMII Gigabit Ethernet PHY

• http://bugs.libre-riscv.org/show_bug.cgi?id=9
• https://github.com/alexforencich/verilog-ethernet/blob/master/rtl/eth_mac_1g_rgmii.v
• https://github.com/pkerling/ethernet_mac - doesn't do RGMII, does GMII.
• https://github.com/enjoy-digital/liteeth - MII RMII GMII RGMII PHY
• https://github.com/adamgreig/daqnet/blob/master/gateware/daqnet/ethernet/rmii.py - RMII in nmigen
• https://github.com/HarryMakes/nmigen-stdio/blob/eth/nmigen_stdio/eth/rgmii.py https://git.m-labs.hk/M-Labs/HeavyX/commit/59d26d148d58d1b385ba935b6e0685d8d3e850c7
• https://www.waveshare.com/dp83848-ethernet-board.htm
• https://www.waveshare.com/wiki/LAN8720_ETH_Board