* <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>