|Developer(s)||Myself086 (Laurent Courville)|
|Platform(s)||Super Famicom (SNES)|
|Programmed in||65C816 assembly, C#|
Project Nested is an open-source Famicom (NES) emulator for the Super Famicom (SNES) written 3/4 in 65C816 assembly and 1/4 C#.
Development of Project Nested started as a private SNES emulator on PC, of which its interpreter was replaced with a recompiler. It ran at full speed, but due to little challenge, a project to emulate the NES on the SNES was started. Official development began in summer 2018 after three years of casual design and coming up with a solution to full performance.
As of v1.3, the model has received minor improvements. The speed was calculated by multiplying the average amount of times each instruction executed per frame and the overhead. However, the maths were 5 percent off on their first implementation. It was mostly implemented after about one month.
The emulator was inspired by the SNES originally being designed for backward compatibility with the NES and a desire to code a JIT (Just-In-Time) compiler.
NES ROMs are converted to SNES ROMs using a JIT (Just-In-Time) and AOT (Ahead-of-Time) compiler (with various options) for Windows, allowing them to run on SNES hardware.
Save files are created after the software title runs for a while. These can then be added to the ROM, often improving performance, varying from little to much, depending on the title.
The following are required:
- Up to 8MB of fast HiROM (slow HiROM support planned)
- 8KB to 256KB of SRAM (16KB+ to create feedback for the EXE)
- A battery if the software title requires it
Emulation occurs at up to 60FPS (frames per second) with audio support, but occasional minor slowdown may occur. Software titles using mappers 0-4 and 7 are playable, with mappers 1 and 4 having minor glitches, which may reduce compatibility, mappers 5, 6, 8, 11, 12, 16, 18, 21-26, 32-34, 36-38, 40, 42 and 66 having potential for future compatibility, mappers 9 and 10 unlikely to be supported due to it being declared impossible to accurately emulate CHR bank switching, and 14 and 17 due to being "copier mappers", and the rest, up to 255, being unknown. Additionally, iNES 2.0 is not supported.
Out of the 534 tested titles, 71 (13.27%) are fully playable, 178 (33.27%) are playable but need a full playthrough to test, 65 (12.15%) are mostly playable, 144 (26.92%) crash in the intro or early in-game, 76 (14.21%) are unplayable and 1 (0.19%) is unlikely to be supported. For example:
- Punch-Out!!! is unlikely to be supported due to using mapper 9/MMC2, due to difficulties in implementing mid-scanline memory bank changes when drawing characters FE or FD, or the harder to implement sprites. The background is easier to implement, however, as the window can be used to draw and switch the characters.
- The graphics in Super Mario Bros. 2 displayed incorrectly and the American version reset after hitting a Shy Guy until v1.4. Some time before the Sharopolis interview on July 10, 2021, the latter issue was reverse engineered and figured out, also fixing many other games that reset.
- Elite is being used as a model to "aggressively" optimize the EXE in AOT compilation, making emulation run at the same speed, or faster if possible. The game runs slowly with flicker and does not support shooting as of v1.3.
Additionally, one fully playable title, Battle City, was mostly playable from v1.1 until v1.3, when it hung after the game over screen with visual glitches in Mesen.
Others run with minor glitches or require certain options, such as NMI at vblank or stack native return, to be disabled. Overall, at least 50% of games are expected to run in the future.