Hello,
There is a stuff out there!
Try a Google search for:
I have gleaned through a lot of this quickly to get some insight and then write my own code and routines.
Let us know what you find useful.
My background is in assembly and C and my understanding of serial communications is much different than someone new to this topic.
This is my world (from ATmega328P datasheet) and how I started programming serial ports:
This low level programming may not be useful to a beginner but has given me a much deeper insight into what is going on at a hardware level and I can better understand serial communications.
:)