* <https://jeffrey.co.in/blog/2014/01/d-flip-flop-using-migen/>
* <http://lists.libre-riscv.org/pipermail/libre-riscv-dev/2019-March/000705.html>
* <https://chisel.eecs.berkeley.edu/api/latest/chisel3/util/DecoupledIO.html>
+* <http://www.clifford.at/papers/2016/yosys-synth-formal/slides.pdf>