Homebrew The ARM7 and ARM9 folders

[MusicOfMusiX]

A very newbie-ish question here. (Also, why am I homebrewing the DS in 2016?)

The DS has two processors, ARM7 and ARM9. But my current project which uses NitroEngine doesn't have the /ARM7 and /ARM9 folders like other projects - Instead it only has /data, /source(with main.c inside) and a single MakeFile.

Building and running the output .nds works. Even sound output(which is only supported my ARM7) with Maxmod!
Is this normal? Are those /ARM7 and /ARM9 folders necessary? And what do I have to do to have both screens active ALONG WITH sound/music?

 

[Technicmaster0]

/ARM7 and /ARM9 are only necessary if you want to run your own code on ARM7. If there is no such folder the project most likely runs on ARM9. But there is code that comes with libnds and it should be sufficient for you, so don't worry about it. You may want to read the makefile for more information.
I suggest you to use NFLib because it's much easier to handle then the 2D engine alone. You have to worry about different VRAM banks etc. if you don't use it.