Anyone know where the definition of the "machine" is for micropython? I'm looking for address map, pin definitions, etc which are in that...

IIRC the "machine" definition is per-board / per-port of MicroPython. Inspecting it in the REPL is probably fastest (that's what I usually do). Otherwise I suspect looking in the individual port source directory for the board you're using would be the place to start looking. There's also some common documentation at https://docs.micropython.org/en/latest/library/machine.html if you're just looking to find out what's usually in that class.

It's been customized for caravel. The pin definition is in the docs directory.

It's also address maps etc. I'm not sure where the official documentation on these things lives