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libretro/emulators/mesen.yml
T
Abdessamad Derraz b3b3880c19 chore: say which repository each source_ref cites
Profiles that read two repositories, a libretro port and its upstream,
now prefix each citation with source or upstream, decided by which tree
carries the cited value at its pin. The emulator pages use the word to
tell libretro glue, emulator code as the port carries it, and the
upstream emulator apart.
2026-10-20 09:23:41 +02:00

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YAML

emulator: Mesen
type: libretro
core_classification: official_port
source: "https://github.com/libretro/Mesen"
upstream: "https://github.com/SourMesen/Mesen"
logo: "https://raw.githubusercontent.com/SourMesen/Mesen2/master/UI/Assets/Mesen.svg"
profiled_date: "2026-03-24"
source_commit: "0102910c39ad1a62bc3f784466f3f67ca9eae335"
core_version: "0.9.9"
display_name: "Nintendo - NES / Famicom (Mesen)"
cores: [mesen, mesens]
systems: [nintendo-nes, nintendo-fds]
notes: |
Mesen is a cycle-accurate NES/Famicom emulator by Sour (the original
NES-only version, archived in 2020 in favor of Mesen2). NES cartridge
games need no BIOS. Famicom Disk System games require the FDS BIOS ROM.
The core tries FdsBios.bin first, then disksys.rom as fallback. Both are
loaded from the system directory root. If neither is found or the file is
not exactly 8192 bytes, FDS games fail to load (BiosMissing).
The Study Box is a Famicom tape-based learning peripheral (mapper 186).
Its BIOS (StudyBox.bin, 256 KB) is loaded the same way. Only needed for
Study Box tape dumps (.stbx format).
MesenDB.txt (game database) is baked into the libretro binary as
MesenDB.inc and loaded in retro_init(). The external file path in
InitDatabase() is never reached in the libretro context.
MesenPalette.pal is an optional custom palette file, loaded only when
the mesen_palette core option is set to Custom. Accepts 192 bytes
(64 colors) or 1536 bytes (512 colors with emphasis combos).
HdPacks go in system/HdPacks/<rom_name>/ -- per-game content, not
system BIOS.
File path construction: retro_load_game() sets
FolderUtilities::SetHomeFolder(systemFolder). All BIOS lookups use
CombinePath(GetHomeFolder(), filename) -- flat, no subdirectories.
No functional divergence between upstream and libretro for BIOS loading.
files:
- name: "disksys.rom"
aliases: ["FdsBios.bin"]
system: nintendo-fds
description: "FDS BIOS ROM"
required: true
size: 8192
validation: [size]
source_ref: "source Core/FdsLoader.cpp:45-59 (LoadBios tries FdsBios.bin then disksys.rom), source Core/FdsLoader.cpp:143-146 (LoadRom validates size == 0x2000)"
note: "Mapped at 0xE000-0xFFFF as PRG ROM bank 0. Core checks FdsBios.bin first, falls back to disksys.rom. Size must be exactly 8192 bytes or BiosMissing is set."
- name: "StudyBox.bin"
system: nintendo-nes
description: "Famicom Study Box BIOS ROM"
required: false
size: 262144
validation: [size]
source_ref: "source Core/StudyBoxLoader.cpp:125-133 (LoadBios), source Core/StudyBoxLoader.cpp:149-152 (LoadRom validates size == 0x40000)"
note: "256 KB BIOS for the Study Box tape peripheral (mapper 186). Only needed for .stbx tape dumps. Size must be exactly 262144 bytes."
- name: "MesenPalette.pal"
system: nintendo-nes
description: "External NES color palette"
required: false
source_ref: "source Libretro/libretro.cpp:301-323 (load_custom_palette), source Libretro/libretro.cpp:405-406 (called when mesen_palette == Custom)"
min_size: 192
max_size: 1536
validation: [size]
note: "Accepts 192 bytes (64 RGB triplets) or 1536 bytes (512 emphasis combos). Falls back to built-in default if size doesn't match."