This is a minimal, bare-metal board support package for the Teensy 3.x
ARM Cortex-M4 MK20DX{128|256) boards from https://www.pjrc.com/
This is based on on work by Karl Lunt and Kevin Cuzner, but stripped
back a bit further.
"make load" will use an installed teensy_loader_cli to download the
firmware to an attached Teensy.
"make dump" will dump your program as assembler with interspersed
code, which is handy when debugging or cycle-counting.
Tested on Linux with https://launchpad.net/gcc-arm-embedded and on
OpenBSD with ports/devel/arm-none-eabi/* (Linaro compiler)