Given an Arduino compatible microcontroller or Raspberry PI (experimental), JTAGenum scans pins[] for basic JTAG functionality and can be used to enumerate the Instruction Register for undocumented instructions. Props to JTAG scanner and Arduinull which came before JTAGenum and forwhich much of the code and logic is based on. Feel free to branch and modify religiously (readme, credits, whatever)
https://github.com/PaulStoffregen/cores/blob/master/teensy4/pins_arduino.h#L36
Part of https://github.com/cyphunk/JTAGenum/issues/12