"In Greek mythology, Tartarus is the deep abyss that is used as a dungeon of torment and suffering for the wicked and as the prison for the Titans." (Wikipedia)
In other words, Tartarus is not a fine place to be. In order to exit from Tartarus, you have to complete the assignment ;).
First, take a look at the slides (check the docs/ folder) for the specifications of this assignement. You MUST NOT touch mcu.c, mcu-api.h.
If you use gcc compiler you can use the following command to compile:
gcc lib-periph.c firmware.c mcu.c -o firmware
Obviously, the main() must be implemented in firmware.c according to specifics (slide n. 9).
Have fun coding with the Tartarus MCU.
If you can't do it yourself, you can find the solution in the branch solution