In school we were taught that the OS does the printf. I think the professors were just trying to generalize to not go on tangents. But, once I learned that no embedded libc variants had printf just no output path, it got a lot easier to figure out how to get it working. I wish I knew about SWO and the magic of semihosting back then. I don't think those would be hard to explain and interestingly it's one of the few things students asked about that in the field I'm also asked how to do by coworkers (the setting up _write).