The folder "mk20dx256" contains a file named " mecrisp-stellaris-mk20dx256.hex". Use the
Teensy Loader application to download via USB to the Teensy 3.1.
To connect to the Forth interpreter, use serial port 1 (not USB, serial). This is Pins 0&1 as shown on the
pinout page. Set terminal software (minicom, screen, picoterm, etc) to 115,200 bps, 8,N,1. You may need to have it automatically add a LF after the CR to get the display correctly.
There are hooks for interrupts (adc0/1, cmp0-2, dac, porta-e, and systick). There is a "dissassembler" in the common code directory, and code for setting the system lock and demonstrating how to turn on/off the led in the "mk20dx256" directory. It's a very basic kernel at the moment ... but fully functional. With your help, I'm sure we could build quite a useful Forth vocabulary.
I'm new to both the Teensy/ARM Cortex-m4 as well as Forth, but will help to the extent I can.