We, as electronics enthusiasts, daily write hundreds of firmware code segments for various microcontrollers. Unlike software, when it comes to debugging microcontroller code, the challenges we face are much more fundamental. I believe that the most common method for debugging firmware is using the good old printf (just like the cout in C++ and println in Java).
When we develop conventional C code for Linux systems, printf works without any hassle. However, to enable the same functionality in microcontrollers, we need to peel away a layer in the C library and find out how exactly printf works.
How printf works?
As you may already know, printf function is implemented within the C library. I will not go through the full printf function definition. If you want you can read http://blog.hostilefork.com/where-printf-rubber-meets-road/. It’s one of the best write-ups I have seen.
However, the important part is, at the end of this function chain, printf calls another function called write. This is a standard system call in Linux, a part of kernel API. However, for microcontrollers, we don’t have such liberties and thus, we have to implement this function ourselves.
Unbox & Beyond 