[J-core] What's involved with putting serial ports on GPIO pins?

[Rob Landley]

Going through fun config tweaks you could do, I remember that when we
couldn't figure out why Numato's USB serial implementation didn't work
on mac (answer, because they hadn't wired up the rts/cts lines between
their serial chip and the USB chip, so the resulting USB packets said
that nothing was ever ready to send or clear to send so MacOS X blocked
endlessly and their stty doesn't have a "disable rts/cts" option)...

Anyway, Jeff worked around this for the liuxcon japan talk by sticking a
serial port on two gpio pins. and soldering two wires and maybe a couple
resistors to a conventional serial port connector.

Could we document how to do that? It seems like a fun "get your hands
dirty" electrical experiment that's less likely to fry the board than
some. :)

Rob