libretro/emulators/nesoid.yml

emulator: Nesoid
type: standalone
core_classification: community_fork
source: "https://github.com/proninyaroslav/nesoid"
upstream: "https://sourceforge.net/p/nesoid/code"
author: "Yongzh (androidemu.com)"
profiled_date: "2026-08-12"
source_commit: "b2ff53fefa56a668aad4a579af85adc672d7a791"
core_version: "2.5"
display_name: "Nintendo - NES / Famicom (Nesoid)"
mode: standalone
cores:
  - "nesoid"
  - "Nesoid"
  - "NESOID"
systems:
  - nintendo-nes
  - nintendo-fds

notes: |
  Android package com.androidemu.nes, launched on the path of the content with
  android.intent.action.VIEW; the activity declares the file scheme with the
  application/zip and application/octet-stream types
  (app/src/main/AndroidManifest.xml:59-71). Two build families answer to that
  package id. Yongzh's own closed builds come first, and 2.3 (versionCode 56)
  and 2.5.0 (versionCode 62) are read here, both carrying his certificate sha256
  744b1df1b3610d58e447d243521a0957cc5f4ebd50b12d2816a92396d1aa32f2 (C=CN,
  O=androidemu.com, freeman.yong@gmail.com). He later published the sources; the
  SourceForge project carried them on and Yaroslav Pronin forked that tree to
  GitHub, where release 2.5-4 (versionName 2.5, versionCode 61, armeabi-v7a,
  certificate O=Free Software CN=Yaroslav Pronin) is the build ES-DE names. The
  SourceForge community rebuild of the same tree (com.androidemu.nes_61.apk,
  certificate O=Alcatraz CN=Birdman) was read beside it. Line numbers are the
  fork's, native addresses are the armeabi library of Yongzh's 2.5.0, and the
  SourceForge tree carries general.c and fds.c byte identical to the fork.

  The emulation core is neslib, FCE Ultra 0.98 reached through the GP2X port
  GPFCE, whose driver and blitters still sit in the tree unbuilt
  (app/jni/neslib/drivers/gp2x/, giz_blit.s). The Android build compiles the
  mapper, board and input sets with its own four file driver
  (app/jni/neslib/Android.mk:12-197), leaves netplay out of the library and
  runs it from Java instead (app/jni/neslib/fce.c:1081,1206,
  app/jni/neslib/drivers/android/netplay.c:1,28), and reduces
  FCEUD_PrintError and FCEUD_Message to empty bodies, so every message the core
  raises is discarded (app/jni/neslib/drivers/android/debug.c:4-11).

  The activity accepts a name ending .nes, .fds or .zip caselessly and refuses
  anything else before the loader runs (EmulatorActivity.java:933-957,
  app/src/main/res/values/arrays.xml:4-8). An archive is opened by the core,
  which keeps the first entry ending .nes, .fds, .nsf, .unf, .nez or .unif, and
  a plain file also opens gzipped (app/jni/neslib/file.c:192-232,250-273).
  FCEUI_LoadGame then tries the iNES, NSF, FDS and UNIF loaders in that order on
  the bytes themselves (app/jni/neslib/fce.c:1180-1187).

  The Disk System BIOS is the file the user has to supply. FDSLoad asks
  FCEU_MakeFName for it, opens it with a plain fopen and reads 8192 bytes into
  the array mapped over 0xE000 to 0xFFFF (app/jni/neslib/fds.c:76,146,160,
  808-843, app/jni/neslib/drivers/android/file.c:3-6). Where that name resolves
  is the one place the two build families differ. Yongzh's builds carry a
  setOption entry fdsRom that duplicates the path the settings screen holds and
  return it from FCEU_MakeFName when set (libnes.so setOption 0x455a4-0x45694,
  setter 0x8804-0x8848, FCEUMKF_FDSROM case 0x8094-0x80ac,
  Nesoid 2.5.0 EmulatorActivity.java:834). The published sources carry neither
  the option nor that branch, so only the fallback remains: FCEUMKF_FDSROM
  formats disksys.rom under the base directory, and nothing on Android ever
  calls FCEUI_SetBaseDirectory, which leaves that buffer empty
  (app/jni/neslib/general.c:46,52-56,215). The settings screen still writes the
  fdsRom preference and still shows the chosen path, but no code reads it back
  (EmulatorSettingsFragment.java:96-99,150-156,195-210,
  app/src/main/res/xml/preferences.xml:240-251). Disk switching went the same
  way: the menu asks the engine for fdsTotalSides and fdsCurrentDisk, which
  Yongzh's builds answer and the fork's does not, the base class returning zero
  for any name (EmulatorActivity.java:417,969,1244-1249,
  app/jni/common/emuengine.h:49).

  The Game Genie ROM is a second path the user picks, kept across both families.
  loadGameGenie passes it to the engine only while the Enable Game Genie switch
  is on, the setter duplicates it into FSettings.GameGenie and OpenGenie reads it
  once the content has loaded (EmulatorActivity.java:870-874,
  app/jni/neslib/drivers/android/nesengine.cpp:242-243,
  app/jni/neslib/svga.c:132-140, app/jni/neslib/fce.c:1201-1203). Both pickers
  list names ending .nes, .rom or .bin
  (EmulatorSettingsFragment.java:179-210, FileChooser.java:157-172).

  A palette named after the content is read from the pal directory of the same
  unset base directory as the disk BIOS, 192 bytes taken as 64 RGB triples; a
  missing file leaves the built-in table in place
  (app/jni/neslib/palette.c:205-224, app/jni/neslib/general.c:216-221,
  app/jni/neslib/fce.c:1212).

  Per content the emulator writes and reads back its own files, all under that
  same base directory: sav/<name>.sav for battery backed cartridge RAM
  (app/jni/neslib/cart.c:641-700), sav/<name>.fds for the modified disk
  (app/jni/neslib/fds.c:845-870,915-930), fcs/<name>.fc<n> states,
  snaps/ screenshots and movie/<name>.fcm recordings
  (app/jni/neslib/general.c:134-195,222-238), and cheats/<name>.cht, which
  FCEU_LoadGameCheats reads at load and FCEU_FlushGameCheats rewrites at close
  (app/jni/neslib/cheat.c:183-208,272-300, app/jni/neslib/fce.c:1080,1213).
  The application writes its own files through Java paths instead: state slots
  at <content>.ss<n> beside the content (StateSlotsActivity.java:39-45,135-140),
  an XML cheat list at <content>.cht, also beside the content
  (Cheats.java:37-46,105-160), key profiles under its data directory
  (KeyProfilesActivity.java:47-60,92-100), PNG screenshots under screenshot/ on
  external storage (EmulatorActivity.java:1258-1281) and a netplay state
  exchanged through its cache directory (EmulatorActivity.java:1292-1293).

files:
  - name: disksys.rom
    system: nintendo-fds
    required: true
    min_size: 8192
    validation: [size]
    config_key: "fdsRom"
    description: "Famicom Disk System BIOS"
    note: >-
      Read as 8192 bytes into the 8 KB array mapped over 0xE000 to 0xFFFF. A
      failed open or a short read frees the disk data and ends the load, so no
      .fds content runs; both messages are discarded and the application reports
      only that the ROM failed to load. Nothing else about the image is
      examined, so a longer file passes on its first 8192 bytes and no hash is
      compared. The open is a plain fopen, so neither a zipped nor a gzipped
      copy answers. Yongzh's builds take the path from the fdsRom setting, whose
      picker lists names ending .nes, .rom or .bin; the builds made from the
      published sources ignore that setting and resolve the compiled name under
      a base directory that is never set, which puts it at the root of the
      filesystem.
    source_ref: "app/jni/neslib/fds.c:808-843 (open, read, failure), app/jni/neslib/fds.c:76,146,160 (array and mapping), app/jni/neslib/general.c:46,52-56,215 (name and empty base directory), app/jni/neslib/drivers/android/file.c:3-6 (plain fopen); Nesoid 2.5.0 libnes.so 0x455a4-0x45694 (setOption fdsRom), 0x8804-0x8848 (setter), 0x8094-0x80ac (FCEUMKF_FDSROM returns the set path), Nesoid 2.5.0 EmulatorActivity.java:834"

  - name: gg.rom
    system: nintendo-nes
    required: false
    min_size: 4352
    validation: [size]
    config_key: "gameGenieRom"
    description: "Game Genie add-on cartridge ROM"
    note: >-
      Read only while the Enable Game Genie switch is on and a path is set,
      through a picker listing names ending .nes, .rom or .bin. The first 16
      bytes decide the format: a leading 0x4E is taken as an iNES image, from
      which 4096 bytes of program ROM are read, then 256 bytes of character ROM
      16 KB further in, so such a file needs at least 16656 bytes; anything else
      is read as a raw 4352 byte image. A failed open or a short read leaves the
      Game Genie off and the content still runs. No hash is compared.
    source_ref: "app/jni/neslib/cart.c:475-521 (open and format branch), app/jni/neslib/svga.c:132-140 (setter), app/jni/neslib/drivers/android/nesengine.cpp:242-243, app/jni/neslib/fce.c:1201-1203 (call site), EmulatorActivity.java:870-874, EmulatorSettingsFragment.java:179-193 (picker)"

  - name: "<game>.pal"
    system: nintendo-nes
    required: false
    category: game_data
    unsourceable: "any 64 colour palette the user picks for one title"
    description: "colour palette for one title"
    note: >-
      Opened as pal/<name>.pal under the base directory when content loads, with
      the name taken from the content. 192 bytes are read as 64 RGB triples and
      replace the built-in table, without checking how many arrived, so a
      shorter file leaves the remaining entries unset; a missing file changes
      nothing. The base directory is never set on Android, so the name resolves
      at the root of the filesystem.
    source_ref: "app/jni/neslib/palette.c:205-224, app/jni/neslib/general.c:216-221, app/jni/neslib/fce.c:1212"

exclusion_note: >
  Left out are the files the emulator writes and reads back, which are its own
  state rather than anything a user obtains: sav/<name>.sav for battery backed
  cartridge RAM, sav/<name>.fds for the modified disk, fcs/<name>.fc<n> states,
  snaps/ screenshots, movie/<name>.fcm recordings and cheats/<name>.cht, which
  is reread at load and rewritten at close. The application writes its own set
  through Java paths: state slots at <content>.ss<n>, an XML cheat list at
  <content>.cht beside the content, key profiles, PNG screenshots under
  screenshot/ and the netplay state in its cache directory. The IPS branch is
  unreachable: FCEUMKF_IPS has no call site, and the only patcher applies a .ips
  handed in as the content itself, which the activity refuses before the loader
  runs. The netplay temporary file
  goes with the netplay code, which the Android build does not compile. The
  gg.rom name FCEU_MakeFName builds is never opened, the Game Genie image
  arriving as a path instead. assets/about.html and assets/faq.html are the help
  screens of the application and carry no emulation data.
  ref: app/jni/neslib/general.c:196-213,222-238, app/jni/neslib/cart.c:641-700,
       app/jni/neslib/fds.c:845-870,915-930, app/jni/neslib/cheat.c:183-208,
       272-300, app/jni/neslib/fce.c:1080,1145-1177,1206,1213,
       EmulatorActivity.java:949-957,1258-1293, Cheats.java:37-46,
       StateSlotsActivity.java:39-45,135-140,
       KeyProfilesActivity.java:47-60,92-100, app/jni/neslib/Android.mk:193-197,
       HelpActivity.java:14-22, MainActivity.java:20,
       EmulatorSettingsFragment.java:30-31