[buescher]

I have not used their libraries or tools, but Miro Samek's book is great. There's a C implementation covered in it also. It's a bit of a master class in embedded C programming with careful use of structs and function pointers for "object orientation".

[JohnTordur]

He also has an awesome YouTube channel which goes from pretty much zero and explains many embedded topics.

Oh, and the book is free: https://www.state-machine.com/psicc2