Thanks for all your comments.
@majenjo: Good idea but unfortunately I'm not proficient in Atmega assembly.
@GoForSmoke: thanks but your comment is totally off question :).
@ PaulS: I guess it's a matter of taste/style, at my previous job I had to deal with lots of code like the following:
somearray[someindex].track.geodata.latitude.value = ...
Repeated for tenths of attributes. This is just plain silly and unreadable, IMHO. Sometimes the lines were so long that the right side of the assignment was out of the screen and you had to scroll to understand what was going on. Plus, if someone renamed, for instance, "geodata" to "position", you had to change it all over the place. Using the reference avoids all of this and the fact that you're using an array is actually explicited in the reference definition.