Is there a difference between dihuno and deffro?
No they have exactly the same meaning.
Dihuno is more Southern and Deffro is more Northern.
What is the relationship between "codi" and "ddihuno", or are they two different words?
to wake up (dihuno, deffro) = to stop sleeping
to get up (codi) = to move your body out of bed
There can be a lot of time between those two events :)