Citra MMJ - RetroBIOS

Type	standalone
Classification	Community forks
Source	https://github.com/weihuoya/citra
Version	20251112
Profiled	2026-08-11
Cores	citra-mmj
Systems	nintendo-3ds

Technical notes

Citra fork for Android, shipped as four APKs of the same build per release: the org.citra.emu package, a com.antutu.ABenchMark package, and a StorageAccess variant of each. The user directory is citra-emu at the root of external storage, and Android/data/org.citra.emu/files/citra-emu for the StorageAccess builds. External files live in sysdata/ and nand/ below it. ref: src/android/app/src/main/java/org/citra/emu/utils/CitraDirectory.java:61-94, src/common/common_paths.h:23-29, src/common/file_util.cpp:398-430

InitKeys reads boot9.bin, then the native firm titles in the NAND tree, then sector0x96.bin for the New 3DS firm, then aes_keys.txt. Content left encrypted stops loading with ErrorEncrypted, shown as "ROM Encrypted". ref: src/core/hw/aes/key.cpp:497-508, src/core/file_sys/ncch_container.cpp:348-351, src/android/jni/main_android.cpp:88-90

GetSharedFont tries the shared font system archive, then shared_font.bin, then the regional BCFNT for the CFG region, and ends the session with ErrorSystemFiles when the three fail. The embedded open-source font answers title low ID 0x00014002 only, so CHN, KOR and TWN, which resolve to 0x00014102, 0x00014202 and 0x00014302, depend on a file. Region defaults to the code the ROM declares. ref: src/core/hle/service/apt/apt.cpp:143, src/core/hle/service/apt/apt.cpp:256-272, src/core/file_sys/archive_ncch.cpp:143-148, src/core/hle/service/cfg/cfg.cpp:176-181, src/core/loader/ncch.cpp:179, src/android/jni/config/main_settings.cpp:12

Loading the four regional fonts from sysdata is specific to this fork. ref: src/core/hle/service/apt/apt.cpp:184-228

The APK assets carry those fonts, three system archives, the DLP module and a seeded CFG savegame, and the first run copies them into the user directory without overwriting what is already there. System archives ship as split-off RomFS, picked up beside the .app path the title tree resolves to. ref: src/android/app/src/main/java/org/citra/emu/utils/CitraDirectory.java:192-207, src/android/app/src/main/java/org/citra/emu/utils/CitraDirectory.java:368-399, src/core/file_sys/ncch_container.cpp:726-741

LLE is opt-in per service module and reads the module from the NAND title tree, falling back to HLE when it is absent. There is no title downloader: system titles come from CIA files the user installs. ref: src/core/hle/service/service.cpp:60-107, src/core/hle/service/service.cpp:197-213, src/android/jni/main_android.cpp:278-289

ClCertA is read from NAND title 0x0004001b00010002 and decrypted with the keyslot 0x0D normal key. HTTPS client authentication stays off without both. ref: src/core/hle/service/http_c.cpp:810-884

The published tree does not build as it stands: CitraDirectory.java:349 calls a NativeLibrary.SetBackgroundGLSL that no file declares, and GetBuildDate and GetDeviceIinfo are declared native with no JNI counterpart. Nothing compiled here reads the post-processing shaders the settings screen lists. ref: src/android/app/src/main/java/org/citra/emu/NativeLibrary.java:341-342, src/android/app/src/main/java/org/citra/emu/settings/SettingsFragment.java:397-401

Amiibo dumps are read as .bin files from amiibo/, cheat codes from cheats/<title id>.txt, texture packs and mods from load/. ref: src/android/app/src/main/java/org/citra/emu/ui/AmiiboDialog.java:57-64, src/core/cheats/cheats.cpp:93-110, src/core/custom_tex_cache.cpp:67, src/core/file_sys/ncch_container.cpp:359-365

18 files | 0 required, 18 optional | 18 in repo, 0 missing | 8 with HLE fallback

boot9.bin optional in repo
ARM9 bootrom

• Path: sysdata/boot9.bin
• System: nintendo-3ds
• Size: 64.0 KB
• Validation: size
• Source: src/core/hw/aes/key.cpp:135-205, src/core/hw/rsa/rsa.cpp:49-80
• AES key section read at offset 55760, RSA modulus and exponent at 0xB3E0 and 0xB4E0. Both readers bail on any other size.

aes_keys.txt optional in repo
AES key slots

• Path: sysdata/aes_keys.txt
• System: nintendo-3ds
• Source: src/core/hw/aes/key.cpp:428-493, src/core/hw/aes/key.cpp:497-508
• Platforms: bizhawk, emudeck, retrodeck
• One name=hex pair per line, slot0x<NN>Key<X|Y|N> and common<N>. Read last, so it overrides what boot9.bin and the native firm titles set.

sector0x96.bin optional in repo
New 3DS NAND secret sector

• Path: sysdata/sector0x96.bin
• System: nintendo-3ds
• Size: min 17 B
• Validation: size
• Source: src/core/hw/aes/key.cpp:309-345, src/core/hw/aes/key.cpp:380-386, src/common/assert.h:30-35, src/common/assert.h:59-62
• First 16 bytes decrypt the slot 0x15 KeyX of the New 3DS safe mode native firm, title 0x0004013820000003. A file of 16 bytes or less trips a live assert: Android compiles out ASSERT_MSG, not ASSERT.

seeddb.bin optional in repo
game seed database

• Path: sysdata/seeddb.bin
• System: nintendo-3ds
• Source: src/core/file_sys/seed_db.cpp:12-57
• Platforms: bizhawk
• Seed-encrypted titles from firmware 9.6 onwards. An empty database is written when the file is absent.

00000000.app.romfs optional in repo HLE fallback japan, north-america, europe, australia
shared font system archive, title 0x0004009b00014002

• Path: nand/00000000000000000000000000000000/title/0004009b/00014002/content/00000000.app.romfs
• System: nintendo-3ds
• Source: src/core/hle/service/apt/apt.cpp:124-182, src/core/file_sys/archive_ncch.cpp:143-148
• First step of the shared font chain, holding cbf_std.bcfnt.lz in its RomFS. This title low ID is the one the embedded open-source font answers.

00000000.app.romfs optional in repo china
shared font system archive for CHN, title 0x0004009b00014102

• Path: nand/00000000000000000000000000000000/title/0004009b/00014102/content/00000000.app.romfs
• System: nintendo-3ds
• Source: src/core/hle/service/apt/apt.cpp:124-182, src/core/file_sys/archive_ncch.cpp:132-158
• Holds cbf_zh-Hans-CN.bcfnt.lz. No embedded replacement answers this title low ID.

00000000.app.romfs optional in repo south-korea
shared font system archive for KOR, title 0x0004009b00014202

• Path: nand/00000000000000000000000000000000/title/0004009b/00014202/content/00000000.app.romfs
• System: nintendo-3ds
• Source: src/core/hle/service/apt/apt.cpp:124-182, src/core/file_sys/archive_ncch.cpp:132-158
• Holds cbf_ko-Hang-KR.bcfnt.lz. No embedded replacement answers this title low ID.

00000000.app.romfs optional in repo taiwan
shared font system archive for TWN, title 0x0004009b00014302

• Path: nand/00000000000000000000000000000000/title/0004009b/00014302/content/00000000.app.romfs
• System: nintendo-3ds
• Source: src/core/hle/service/apt/apt.cpp:124-182, src/core/file_sys/archive_ncch.cpp:132-158
• Holds cbf_zh-Hant-TW.bcfnt.lz. No embedded replacement answers this title low ID.

shared_font.bin optional in repo HLE fallback
system shared font, legacy dump

• Path: sysdata/shared_font.bin
• System: nintendo-3ds
• Source: src/core/hle/service/apt/apt.cpp:230-246, src/core/hle/service/apt/apt.cpp:256-272
• Copied whole into the shared memory block, so the file carries the 0x80 byte APT header. Tried after the system archive and before the regional BCFNT files.

cbf_std.bcfnt optional in repo HLE fallback japan, north-america, europe, australia bundled
shared font for JPN, USA, EUR and AUS

• Path: sysdata/cbf_std.bcfnt
• System: nintendo-3ds
• Source: src/core/hle/service/apt/apt.cpp:184-228, src/core/file_sys/archive_ncch.cpp:143-148
• Read to offset 0x80 of the shared memory block, so the file is a bare uncompressed BCFNT. Selected for every CFG region other than CHN, KOR and TWN. The embedded open-source font answers the archive request first, so this file is only reached when that archive path is taken out.

cbf_zh-Hans-CN.bcfnt optional in repo china bundled
shared font for CHN

• Path: sysdata/cbf_zh-Hans-CN.bcfnt
• System: nintendo-3ds
• Source: src/core/hle/service/apt/apt.cpp:184-228, src/core/hle/service/apt/apt.cpp:256-272
• Selected when the CFG region is CHN. The embedded font does not cover archive 0x00014102, so the session ends with ErrorSystemFiles without this file or shared_font.bin.

cbf_ko-Hang-KR.bcfnt optional in repo south-korea bundled
shared font for KOR

• Path: sysdata/cbf_ko-Hang-KR.bcfnt
• System: nintendo-3ds
• Source: src/core/hle/service/apt/apt.cpp:184-228, src/core/hle/service/apt/apt.cpp:256-272
• Selected when the CFG region is KOR. The embedded font does not cover archive 0x00014202, so the session ends with ErrorSystemFiles without this file or shared_font.bin.

cbf_zh-Hant-TW.bcfnt optional in repo taiwan bundled
shared font for TWN

• Path: sysdata/cbf_zh-Hant-TW.bcfnt
• System: nintendo-3ds
• Source: src/core/hle/service/apt/apt.cpp:184-228, src/core/hle/service/apt/apt.cpp:256-272
• Selected when the CFG region is TWN. The embedded font does not cover archive 0x00014302, so the session ends with ErrorSystemFiles without this file or shared_font.bin.

00000000.app.romfs optional in repo HLE fallback bundled
Mii data system archive, title 0x0004009b00010202

• Path: nand/00000000000000000000000000000000/title/0004009b/00010202/content/00000000.app.romfs
• System: nintendo-3ds
• Source: src/core/file_sys/ncch_container.cpp:726-741, src/core/file_sys/archive_ncch.cpp:132-136
• Split-off RomFS served in place of the NCCH the title tree resolves to. An open-source replacement is built into the binary.

00000000.app.romfs optional in repo HLE fallback bundled
country list system archive, title 0x0004009b00010402

• Path: nand/00000000000000000000000000000000/title/0004009b/00010402/content/00000000.app.romfs
• System: nintendo-3ds
• Source: src/core/file_sys/ncch_container.cpp:726-741, src/core/file_sys/archive_ncch.cpp:137-142
• Split-off RomFS served in place of the NCCH the title tree resolves to. An open-source replacement is built into the binary.

00000000.app.romfs optional in repo HLE fallback bundled
bad word list system archive, title 0x000400db00010302

• Path: nand/00000000000000000000000000000000/title/000400db/00010302/content/00000000.app.romfs
• System: nintendo-3ds
• Source: src/core/file_sys/ncch_container.cpp:726-741, src/core/file_sys/archive_ncch.cpp:150-157
• Split-off RomFS served in place of the NCCH the title tree resolves to. An open-source replacement is built into the binary.

00000000.tmd optional in repo HLE fallback bundled
title metadata of the DLP module, title 0x0004013000002802

• Path: nand/00000000000000000000000000000000/title/00040130/00002802/content/00000000.tmd
• System: nintendo-3ds
• Source: src/core/hle/service/am/am.cpp:428-464, src/core/hle/service/am/am.cpp:466-501, src/core/file_sys/title_metadata.cpp:19-34
• Read to resolve the content ID of index 0, which the shipped metadata gives as 0x1f. Without it the path falls back to content ID 0 and the module is not found.

0000001f.app optional in repo HLE fallback bundled
DLP system module, title 0x0004013000002802

• Path: nand/00000000000000000000000000000000/title/00040130/00002802/content/0000001f.app
• System: nintendo-3ds
• Source: src/core/hle/service/service.cpp:78, src/core/hle/service/service.cpp:197-213
• Loaded as a process when LLE is enabled for DLP, otherwise the HLE service is installed.

Generated on 2026-10-10T11:26:01Z