FCEUmm Next is a modified libretro core originally based on libretro/fceumm, now evolved with significant custom changes and enhancements. It’s designed to be used with RetroArch or any libretro-compatible frontend.
FCEUmm is a Nintendo Entertainment System / Famicom emulator. It currently supports a wide number of carts, including support for Family Computer Disk System and Vs. Unisystem.
It is a fork of FCEU "mappers modified", an unofficial build of FCEU Ultra by CaH4e3, which supports a lot of new mappers including some obscure mappers such as one for unlicensed NES ROM's using the Libretro API.
What this fork is
FCEUmm Next aims to provide faster updates, new features, and better integration with the Libretro API. It includes a complete rewrite of the mapper interface and updates to some code sections that required improvement. The goal is to retain a consistent code-style, enhance the existing framework while ensuring seamless integration with the Libretro ecosystem, among other changes.
These updates were initially intended to be merged into the main fork, libretro-fceumm. However, when I submitted my PRs, they were rejected without clear explanations or meaningful feedback. The concerns raised — particularly about multicart support — were vague, with no actionable details provided.
Since the regressions were likely fixable if the issues had been communicated clearly, and because anything already existing in libretro-fceumm could be moved or added to FCEUmm Next without major difficulty, the lack of concrete information made progress impossible. Despite this, the same changes and concepts I had initially submitted were later submitted and merged, without any explanation as to why my contributions were rejected in the first place.
With no proper communication, or transparency, I decided to create FCEUmm Next to continue pushing forward with the necessary updates and features that were blocked or delayed in the original project.
Changes/Differences
Mapper Support
- Additional mappers supported
- Mapper fixes and updates
- Refactored common mappers (MMC1, MMC3, VRC2/4, others) into a modular, reusable interface
- Use NES 2.0 info for supported input types (when available)
- Propagate FCEU_MemoryRand() to initialize mapper WRAM, CHR RAM, and other cartridge memory types
- FCEU_gmalloc default init state based on FCEU_MemoryRand()
Audio Improvements
- Refactored common expansion audio (FDS, MMC5, VRC-series, others) into a modular, reusable interface
- Replaced on/off audio options with volume controls
- Added volume controls for expansion audio (FDS, MMC5, VRC6, VRC7, Namco163, Sunsoft5B)
- Fixed audio controls not muting some channels in low-quality mode
- Fixed low volume issue
- Updated VRC7 sound code (emu2413)
- Replaced Sunsoft 5B sound code with emu2149 for improved accuracy (including envelope and noise emulation)
- Rewrote Namco163, VRC6, and FDS sound codes
- NSF: Fixed waveform visualizer
- NSF: Added support for multiple audio chips (WIP)
- Added NSFE support
Input Support
- Additional input options: SNES Mouse, SNES Gamepad, PowerPad A/B, VirtualBoy Controller, etc.
- Vs. System input rework: fixes input issues, updates database, and reworked palettes
Video & Display
- Variable overscan cropping options (top, bottom, left, right)
- 32-bit color format by default, with optional 16-bit (PSP/3DS default 16-bit, PS2 ARGB1555)
Hotkeys & State
- Assign F12 as Hard Reset (PowerNES) hotkey
- Added missing state variables for runahead compatibility
Enhancements & Fixes
- Write instructions now update the databus (backport: PR #659 )
Applied bisqwit's deemphasis method- Added support for 512 palettes with bisqwit's deemphasis (FCEUX)
- Fixed possible buffer overflow caused by uninitialized emphasis buffer
- Miscellaneous under-the-hood improvements (Libretro, sound, etc.)
Button/Key Changes/Additions:
- F12 - Hard-Reset
- L1 - Change Disk Side in FDS
- R1 - Insert/Eject Disk in FDS
- L2/R2 - Insert Coins for slot 1/2 respectively in Vs. Unisystem and some coin-operated mappers.
- holding L2 and pressing LEFT/RIGHT will change internal palette
- L3 - simulate Famicom Player 2 Microphone (probably)
Compiling:
-
Linux: make clean && make
-
Windows (MSYS2): make clean && make
Input Devices
- Standard Joypad (4-players)
- NES Zapper
- SNES Pad
- SNES Mouse
- Virtual Boy Controller
- Power Pad A/B Mat
- Family Trainer A/B Mat
- Arkanoid Paddle
- Hyper Shot Gun
- Hyper Shot Mat
- Party Tap
- Exciting Boxing Punching Bag
Additional Notes:
This core is a work-in-progress! Expect breakage or regressions. With the massive changes, savestates will not be compatible between versions or commits. SRAM or battery saves are mostly compatible. NES 2.0 headered rom is prefered in most cases.
PS2/PSP targets are special cases and may not include some enhancements and/or maybe break in future (unless someone wants to step in to maintain them) since i dont have a way to test it on my own.
emu2413 - https://github.com/digital-sound-antiques/emu2413 emu2149 - https://github.com/digital-sound-antiques/emu2149
25.09.29
- m464 - Fixed reset to menu
- m396 - Add submapper support
- Add mapper 182,variant of mapper 114, (needs testing)
25.09.22
- Fixed issue in square audio not silencing when a sweep overflow has occured
25.09.20
- Add mappers 273, 367, 378, 474, 475, 476, 477, 478, 480, 482, 483, 484, 485, 486, 488, 489, 490, 491, 492, 494, 495, 498, 499, 503, 504, 505, 506, 507, 508, 509, 510, 511, 536, 537, 542, 545, 546, 563, 564, 565, 566, 567, 568, 569, 570, 571, 572, 573, 574, 575, 576, 577, 578, 579, 580, 581, 582, 583, 584, 585, 586, 587, 588, 589, 590, 591, 592, 594, 595. (needs testing)
25.09.16
- Improve MMC5 audio: implement length counters and envelope output for square channels, including $5015 status reads, to support Koei game effects and volume modulation and others that may need it.
25.07.22
- FDS, support for QD format
25.05.2x
- Mapper rebuilds (start using structs, new naming scheme, etc)
- Fixed mapper 48
- Fixed mapper 19
- Fixed mapper 56 incorrect sprite image caused by wrong address mask on register writes (regression).
- Fixed bug in vrc24 module that caused incorrect chr bank data (regression)
- Add helpers to easily set or remove read/write access to cpu pages
- Revert opcode update that broke a few games (opcode 0xAB, 0x9C, 0x9E)
- Fixed mirroring in mapper 302
- Add support for submapper 1 in mapper 396
- Add support for submapper 1 in mapper 458
- Add mapper 493
25.04.25
- moved to a standalone repo
25.04.24
- lots of changes to write
24.10.04
- Add option to disable ppu color emphasis
- Fix allocation and deallocation of CHR-RAM
24.10.03
- mmc3: Fix regression in handling 4-screen mirroring (fix Rad Racer 2)
- m064: Rework irq (fix Skull and Bones)
24.10.01
- Add mapper 470 (backport fceumm)
24.09.30
- Add mapper 515
- ps2: Update upload-artifacts to v4
- make x24c02 only read/write state if I2C address match, backport from fceux (fix SD Gundam Gaiden 2)
24.03.15
- Add mapper 284 (UNL-DRIPGAME, only works in newppu for now)
24.03.06
- Rewrite mapper 6 / 8 / 12.1 / 17
24.03.03
- Add mapper 561
- Add mapper 562
24.02.26
- Add New PPU support (backport from FCEUX)
- Fixed mapper 124
24.02.25
- Fix mapper 156
- Fix support for Ys Definitive Edition (romhack)