lolSnes git 01/01/2014

  1. Scyther
    I hope this project will bring some new life into the SNES-on-DS scene. It looks like all the existing emulators for the DS are dormant or discontinued, which is sad.

    lolSnes is a project I had started two years ago. I wanted to make a SNES emulator for the DS, that could render most sane games without glitches. But I followed a wrong approach with the PPU side: trying to make a line-accurate software renderer. The DS just isn't powerful enough to handle such a renderer. That discovery pretty much shattered my motivation and the project stayed dormant for two years.

    And now, for some reason, I felt like working on it again. I trashed the software PPU attempt and coded the PPU using the DS's 2D video hardware.

    So far, SMW is playable, to some extent. The background layer tends to obstruct text like menus and info boxes because per-tile priorities aren't emulated yet.

    You also can't get past Donut Plains 2: for some reason, the camera keeps rewinding and moving forward a bit at the start of the level, keeping you from going further. Aside from this bug, gameplay is near perfect. The game also runs at fullspeed (albeit with a speedhack).

    What's in?

    * Main CPU: 99% -- all opcodes emulated, may miss some unimportant bits though
    * PPU: ~30% -- Mode 1 BG and OBJ supported, as well as some of the priority
    * SPC700: 80% -- most useful opcodes implemented, as well as I/O (SPC/CPU comm, timers)
    * DSP: 0% -- what it says. No sound yet.
    * Joypad input for joypad 1


    * There is no interface for selecting a ROM-- it is hardcoded to load snes/rom.smc
    * Tearing and black pixels tend to appear when backgrounds scroll, because writes to the BG scroll registers are applied directly and not synced to the DS display
    * CPU bugs are hidden in the main CPU core, and possibly the SPC700 core. They may bite you when you expect it the least.

    Github repo

    For those who are interested, the source code is available in a Github repo.

    Even though it isn't explicitly mentioned in the code files, the code is under the GPL license.

    A lot of this is written in ARM ASM. If you don't have some knowledge of ARM ASM and GCC calling convention, the code may look like black magic to you...

    If you're crazy enough to try it out

    At the time of writing this, the latest revision should run on a DS, but there is no guarantee that it will always be the case. I mostly test on desmume, which is not 100% accurate. As such, issues may go unnoticed on desmume and cause trouble on a DS. Such issues being mainly accesses to invalid addresses-- desmume doesn't seem to emulate the memory protection unit.

    Feel free to try it though, any feedback is recommended.

    You need a recent devKitPro to build it. Then, place lolSnes.nds on your flashcart/whatever. Create a folder named 'snes' there, and put your ROM in it, under the name 'rom.smc'.

    Run lolSnes.nds and it should automatically load your ROM. You'll get to see it either launch your game, or explode.

    Have fun! ;)