MasterGear - RetroBIOS¶
Technical notes
Sega 8bit emulator by Marat Fayzullin, covering Mark3, MasterSystem, MasterSystem 2, GameGear, SG1000, the keyboard-equipped SC3000 and the disk-based SF7000. Two builds of version 4.9 were read. The Android package com.fms.mg is sold on Google Play and not carried on the author's site, so it came from a mirror; that copy has versionName 4.9, versionCode 4900, sha256 11c3f3331d6774739c11dfd604f74f545a17ceba3feb7fb294f02bd80943af35, md5 2cb4df11254f8525e0a2253677450555, and is accepted because its v1 certificate is the author's own key, CN=Marat Fayzullin O=Garage Research issued 2011, fingerprint d09469e9b550cbc9005d3bd089f3df5f0ba89cba71cdd3b33736a0382d6f9848, beside a Play distribution source stamp in the signing block. The free MG 4.9 builds for Windows and Ubuntu, published by the author, were read next to it and open the same files. The native libraries keep their symbol tables, so the Android readings below cite libmain.so offsets in the x86_64 slice; the arm64-v8a, armeabi-v7a, armeabi and x86 slices carry the same filename set. No source has ever been published: the site states the code is not available to the general public and the documentation repeats it, while ColEm and fMSX on the same site ship source archives. ref: MG-Android-4900.apk META-INF/CERT.RSA, https://fms.komkon.org/MG/, MG.html "There is no version of MG for my Unix!", MG49-Windows-bin.zip, MG49-Ubuntu-x86-bin.tgz
SF7000.ROM is the only system ROM either binary names, and it is read through the cartridge loader. ResetSMS loads it whenever the requested hardware becomes SF7000; LoadROM returning zero makes ResetSMS clear the SF7000 bits and restore the previous hardware, so LoadDSK finds the machine still is not an SF7000, ejects the image and fails, logging "Failed switching into SF7000 mode." when verbose output is on. Nothing about the file is checked: the size comes from a seek to the end, is rounded up to the first power of two of at least 16kB, and the buffer is filled with FFh before the read, so a short image is padded rather than refused. When bit 15 of the mode word is set, a successful load is followed by patching the image at eight fixed addresses, 0008h, 0010h, 0018h, 0020h, 0028h, 0030h, 107Ch and 10F8h, with an EDh FEh C9h trap and a checksum byte. ref: libmain.so ResetSMS 0x435a0-0x43b0d (LoadROM 0x43604, revert 0x4367d, patch loop 0x43619-0x4367b), LoadROM 0x43c80-0x4451a (open 0x43db3, size 0x43dfa-0x43f1a, read 0x43f4f), LoadDSK 0x46db0-0x46ecb, MG49-Ubuntu-x86-bin mg 0x3d0fd-0x3d124, 0x3c330 (0x3ca58)
The other machines need no file. SEGA consoles boot from a small ROM that switches itself off and hands the hardware to the cartridge, which MG does not emulate, so MasterSystem, GameGear, SG1000 and SC3000 start straight into the cartridge. SC3000 mode adds the keyboard and 32kB of RAM, and its BASIC arrives as a cartridge like any other program: the packaged title database keys Basic 2.10 and Basic 3.10 by cartridge CRC32 under the SC3000 heading. ref: MG.html "What are MasterSystem and GameGear?", "How do I use SC3000 keyboard?", assets/names.dat
On Android one directory holds everything. MainActivity hands EMULib.k() to
jniStart, which copies it into the buffer GetHomeDir returns and passes that
same buffer to SetPrivateDir. Every open goes through mopen, then
OpenRealFile, which tries the name as given and again as
10 files | 1 required, 9 optional | 5 in repo, 5 missing Categories: 1 BIOS, 9 game data
SF7000.ROM required in repo
SF7000 IPL, read into the cartridge window before the machine starts
- System: sega-sf7000
- Size: 8.0 KB
- Source:
libmain.so ResetSMS 0x435a0-0x43b0d,LoadROM 0x43c80-0x4451a,LoadDSK 0x46db0-0x46ecb,MG49-Ubuntu-x86-bin mg 0x3d0fd-0x3d124,MG.html "How do I use SF7000 disk images?" - Loaded whenever the hardware becomes SF7000, and the only fixed ROM name in the binary. A failed open drops the emulator back to the previous hardware, which makes every disk image refuse to mount. The loader checks neither length nor contents, so the documented 8kB image is padded to 16kB with FFh and no hash is compared. Opened by bare name, so it resolves against the working directory and, on Android, against the home directory as well, and a gzipped copy answers too.
MasterGear-Cheats.zip optional in repo game_data
cheat database read by the Cheatopedia browser
- Source:
Cheatopedia.java:340-391,Cheatopedia.java:414,Cheatopedia.java:565-584 - The Android build ships no cheat set. Cheatopedia looks for ROOT.chts in the package assets, then in the home directory and its subdirectories, and takes it from this archive in the Downloads directory, unpacking it into
/Cheats when it is newer. The author publishes it at fms.komkon.org/EmuAndroid/ and the copy read here carries ROOT.chts plus crystal-warriors-gg, dragon-crystal, gamegear, phantasy-star and ultima. No hash is recorded because the archive is refreshed in place at that address.
custom.chts optional missing game_data
user cheat sets added to the Cheatopedia menu
- Source:
Cheatopedia.java:504-508,Cheatopedia.java:565-584,MasterGear-Cheats.zip ROOT.chts,EmuAndroid "I want to add my own cheats to the Cheatopedia" - Pulled in by the File= directive that ROOT.chts carries, written out as /sdcard/MasterGear/custom.chts, and reached through the same lookup as any other set: package assets, then an absolute path, then the cheat directory.
names.dat optional in repo game_data bundled
title database keyed by system and CRC32
- Size: 20.7 KB
- Source:
FileInfo.java:260-308 - Parsed from the package assets as lines of key colon title, keys reading SMS-0274179A. The copy at
/names.dat is read straight afterwards into the same map, so user entries extend and override the packaged ones.
changelog.html optional missing game_data bundled
release history shown from the Android menu
- Size: 66.6 KB
- Source:
EMULib.java:1075,EMULib.java:1104 - Read whole from the package assets, and shown again through file:///android_asset/. No copy outside the package is consulted.
Controls.png optional in repo game_data
virtual joystick skin
- Source:
MainActivity.java:1809,LayoutEditor.java:99,EmuAndroid "Can I set my own virtual joystick images?" - Read as
/Controls.png when the joystick shape is set to Custom Skin, and by the layout editor. The author publishes a 320x276 template at fms.komkon.org/EmuAndroid/Controls.png to draw over.
Backdrop.png optional in repo game_data
backdrop drawn around the emulated screen
- Source:
MainActivity.java:1047-1051 - Read as
/Backdrop.png while the decorum option is on. A built-in drawable stands in when the file is absent.
<game>.back.png optional missing game_data
backdrop for one title
- Source:
MainActivity.java:1047-1049 - Named from the loaded ROM path and preferred over the shared backdrop for that game.
<game>.ips optional missing game_data
IPS patch applied to the loaded cartridge
- Source:
libmain.so LoadROM 0x444bf-0x444e1,LoadFile 0x43b10-0x43b9f,LoadIPS 0x467e0,ApplyIPS 0x5b1e0 - Named from the ROM path by MakeFileName and applied by LoadIPS when present. A patch opened by hand reaches the same loader through LoadFile.
<name>.cht optional missing game_data
cheat codes loaded from the file selector
- Source:
libmain.so LoadFile 0x43b10-0x43b2f,suffix compare 0x46a40-0x46b8f,LoadCHT 0x46b90-0x46c9b,MenuSMS 0x48bf1 - LoadFile compares the tail of the name against .CHT through a case folding compare and sends a match to LoadCHT, so the name is the one the user picked rather than one derived from the ROM path. The built-in menu writes edited cheats back under the same extension.
Generated on 2026-08-23T16:12:06Z