Links:
* <http://www2.eng.cam.ac.uk/~dmh/4b7/resource/section14.htm>
+* <https://www10.edacafe.com/book/ASIC/CH02/CH02.7.php>
* <https://ftp.libre-soc.org/Pin_Control_Subsystem_Overview.pdf>
* <https://bugs.libre-soc.org/show_bug.cgi?id=50>
* <https://git.libre-soc.org/?p=c4m-jtag.git;a=tree;hb=HEAD>