Hint: you can find pre-compiled .hex files for all SimonK versions from here : https://github.com/sim-/tgy/downloads
To upload on OS X (for example Hobby King 30A ESC 3A UBEC):
avrdude -c usbasp -pm8 -U flash:w:/Users/xxx/Downloads/tgy_2012-09-30_0d3e617/bs_nfet.hex