So your entry point to homebrew must be able to use CSND. CHT/.CHX (text format) with the same filename in the same folder as your ROM. Games that slow on the Old 3DS will benefit from the higher clock speed that the New 3DS offers (In some New 3DS set ups you may have to manually force the clock speed up to enjoy the performance boost). It has a much high compatibility than existing SNES emulators on the 3DS because it uses Snes9x 1.43 as a base, and is a good alternative if your existing emulators cannot play all the games. It also runs games that use the SA-1 chip (Super Mario RPG, Kirby's Dreamland), SuperFX chip (Yoshi's Island, Star Fox etc) but these games run with plenty of frame drops. It supports games that use CX4 chip (Megaman X2/X3), the SDD-1 chip (Star Ocean, Super Street Fighter 2 Alpha), DSP chip (Super Mario Kart). It runs many games at full speed (60 fps). Snes9x for 3DS is a high-compatibility SNES emulator for your Old 3DS/2DS.
