Ooh all the pretty colours.
Anyway
- arm7.bin
- arm9.bin
fnt.bin is common to various ROM unpacking tools. Short for something like file name table. Likely of no relevance here.
arm7 in most commercial games is just a library binary. It runs on the ARM7 processor in the DS and is usually used to handle boring operations. Some homebrew differs here, and some people use them as injection points. To get an idea of how banal they are you can usually swap them with games from about the same time (or just before or after) and the game will run exactly as it did before, indeed the "ARM7 swap" was once a fix that allowed certain games to work before a user's given flash cart had been updated to support it.
arm9 then is the big boy. It contains the code that runs on the ARM9 processor which for most commercial games is everything that goes. It runs the game logic and everything else. Often they are augmented by so called overlays which are small sections of code the DS will fetch and stick in a given area of memory before another is dropped in, and another, and another as demanded, and yes multiple can be in at once depending upon what goes. Best coding practice would say there should not be text, graphics, audio, levels and such in the ARM9 or overlays but that means nothing and loads of games have examples of all of it in there.
If text is in there and needs to be translated it is a pain to handle compared to more conventional text in external files that better game devs will use. This primarily comes from things having to be the same size or smaller and padded out unless you can repoint in the binary, which is a pain compared to said external files. If you need extra space, don't fancy finding some in memory (there is a desmume build geared for it, and more conventionally an older build of dsatm did so called deadbeef padding which allows you to look at the memory during play and see what had not yet been used) and your game is a wifi game I tend to find a lot of error message codes are in the binary so provide you with extra space as wifi error codes are not so useful these days.
I have not knowingly seen .r00 files before (I assume they are not rar files), or at least they are not ringing a bell as far as being a known packing format (see something like NARC, or their compressed form CARC). However many devs would do custom formats so no great shocker there, indeed figuring out such things is probably the bread and butter of DS ROM hacking. Just because one is a model does not mean they all are.
