BGB version 1.6.2

email: bgb at bircd dot org

this is a gameboy/color emulator/debugger for win32 which will probably never be finished


no warranty of any kind, use at your own risk. This program is guaranteed to do nothing but taking disk space. Don't blame me if it damages your computer, or erases your hard drive, etc. Using copyrighted roms with an emulator is illegal if you don't own the real cartridge or have explicit permission from the copyright holder. If you choose to do so, that is your responsibility.

table of contents

right click menu
default keys
features in this version
supported platforms/system requirements
accurate emulation and broken PD roms
known problems
SAV (battery) file format
camera emulation
options window
GameGenie/GameShark cheat
cheat searcher
debugger hotkeys
expressions, breakpoint conditions, and debug messages
Commandline parameters
Demo recording/playback
How to make bgb run faster if you have a slow computer
full screen mode
game link
AVI recorder
Note for speedrun or "race" use
version history

right click menu:

Click the right mouse button in the emulator window to get the popup menu, from which you can access the options and functions.

default keys:

numpad +fast forward
numpad *reset gameboy
numpad -cheat codes on/off
AB button
SA button
ShiftSelect button
EnterStart button
F2save state
F3select state
F4load state

features in this version:

supported platforms/system requirements

BGB x86 version tested to work on windows 95b, 98 SE, NT 4, XP, Windows 7, 8.1, 10, and 11. Wine on linux and OS X. Requires DirextX 7 or later, OpenGL, and winsock 2. PNG support requires windows XP or later.

Minimum pentium 133 MHz, 16 MB RAM (windows 95b), minimum recommended pentium 200 MHz or faster, 32 MB RAM (windows 98). soundcard and joystick/gamepad are optional. A videocard with 3D hardware acceleration is recommended. BGB runs perfectly on an atom netbook.

BGB x64 version tested to work on Windows XP 64 bits, Windows 7, 10, 11, and Wine on linux and OS X.

accurate emulation and broken PD roms:

by default, BGB emulates the real hardware very accurately, including behavior that some broken PD/unofficial roms may have problems with. These roms would also fail on real hardware, or on a real cartridge: they rely on an inaccurate emulator, or a flashcart. in the "except" tab, one can choose "Troubleshoot broken PD roms", and then set aspects of deliberately inaccurate emulation, to see which one a broken PD rom depends on. Choosing "Emulate as in reality" disables and locks out all inaccuracies and should be done if not trying to fix a problem with a bad rom.
one can also set "break on ..." settings to break (go to the debugger) if a rom misbehaves.
note that if you enable any "break on" settings, or set breakpoints of any kind, bgb will run in "debug mode", and will be about twice as slow because of extra checks. this is done to allow bgb to run as fast as possible if debug features are disabled.

known problems:

SAV (battery) file format

SAV files are raw battery ram images, except for MBC3 RTC games, where 48 bytes of RTC data is appended, in a way that is compatible with Visualboy Advance and some other emulators. Some emulators are unable to load such SAV files, for example 3ds VC. If you encounter this problem, you can disable "Save RTC in SAV file (VBA compatible)" in the settings, "misc" tab. To "fix" an existing SAV file, load the game and close it again.

camera emulation:

BGB emulates the gameboy camera and the image source can be an image file (including BMP and PNG), a built in test pattern which tests grey scales and movement, and a webcam. Webcam is done using DirectShow 9, and is confirmed to work on Windows XP, Windows 7, and Windows 10, confirmed to work on Wine 6.0.0 and later, and found to not work on Wine 5. BGB will work on systems without DirectX 9 but without webcam support. If you have multiple webcam sources, you can choose one from a list.

When a camera ROM is loaded, by default, the Camera Control window will show, for changing camera related settings. This can also be disabled with a checkbox in the window. The Camera Control window can also be accessed through the rightclick menu whenever a camera ROM is loaded, and through the "Other" menu otherwise. "Show preview" will show what the camera is seeing, depending on current settings. This also works if no ROM is loaded. Click "Apply" to update the preview after changing the camera source.

When the webcam is being turned on because you show the preview, or because you load a camera ROM, bgb may hang for a second up to maybe 20 seconds (seen on windows XP with an old webcam).

Development and debugging of camera ROMs: The camera's control registers and functionality are emulated accurately, based on research with a real gameboy camera, including visually close simulation of combinations of exposure, contrast, N bit, edge enhancement, edge extraction, zero voltage, and Vref. Exposure takes the real/correct time. The camera sensor's full resolution of 128x123 is emulated, of which existing camera ROMs show a 128x112 area. An image file of 128x123 or 128x112 pixels will show native without any resizing or cropping. The camera's IO registers and matrix can be seen and modified in the debugger. To do so, in the data viewer, go to 10:a000, then rightclick and "Force memory visibility".

The "Exposure" setting controls which exposure will show the image as-is. It is a hex value between 0001 and ffff. Default 800. Lower values simulate a brighter environment (as in, outdoors versus indoors) and make exposures faster.

options window:

Popup menu --> Options.
here you can change a lot of settings such as the joypad keys, configure a gamepad/jostick, change the colors of the gameboy screen, and graphics and sound options. Besides obvious "preference" settings, most settings are optimal as default and should not be changed unless trying to fix a problem.

GameGenie/GameShark cheat:

how to use a gamegenie/shark code: press F10, or use the rightclick menu and choose "cheat", to show the cheat window. click "Add". click in the "Code" field, and paste or type the code. optionally, click in the "Comment" field, and enter a description. click "OK". click on the newly added code in the list, and click "Enable".

the cheat window shows a list. you can add/edit/delete cheat entries, with a code and a description. you can load/save the cheats to a file.
meaning of the letters:

The "advanced" checkbox controls whether internal values for the cheat are shown in the list and edit window.

In the cheat edit window, you can either enter a code, and internal values will be displayed, or you can enter internal values, and the corresponding code will be displayed.

For a gameshark cheat, you can either use "enable" to make it work constantly, or "poke" to make it change the ram value once.

Rightclick on a cheat to set a watchpoint (for gameshark codes only), or go to this cheat's ROM or RAM address in the debugger.

cheat searcher:

with the cheat searcher and the debugger, you can make new gameshark and gamegenie cheats

Play the game to the point where you want to influence behavior (for example, the game action itself) press esc to enter debugger. menu: Window -> cheat searcher. select value type (normally 8 bits) and press start.

you may be looking for a value such as "3 lives", in that case, the value in RAM may be 3 as well, but it's not guaranteed.

continue the game, walking around, killing enemies, etc, but making the value you're looking for *not* change (not dying, not getting hurt, etc), use the criteria "equal to the previous value" and search. the number of addresses displayed goes down. you can repeat this a few times. now run the game, but make the value you are looking for change, for example by dying or getting hurt in the game. now search for values which are, for example, "lower than the previous value". the number of matching addresses in the list become smaller each time you run the game and do a search, and you should end up with only one address.

Now, rightclick on the address, and choose "go here in debugger". this will select the address in the ram viewer (on the bottom of the window). then rightclick on that address, and choose "freeze ram value", and enter the desired value. This will create a gameshark code. You can open the cheat window to see the code listed.

if you want to create a gamegenie code, rightclick on the gameshark code, and choose "set watchpoint". Run the game until the value is changed (for example, die in the game), and it should stop and show the code line on which the value is changed. interpret how the code changes the value, and use game genie codes to change bytes in the code - such as changing an instruction to a nop, or change a "number to decrease" (value 01 to 00), in the cheat window, add new code, enter the address, existing and desired values, and a gamegenie code is produced automatically.

debugger hotkeys

A list of shortcut keys that work in the debugger:

F2Toggle breakpoint
F3Step Over
F4Run to cursor
Shift+F4Run to cursor no break
Ctrl+F4Run to cursor reverse
Shift+F8Step out reverse
F5VRAM viewer
F6Jump to cursor
Shift+F7Trace reverse
F7Trace (step into)
F8Step out
Shift+F8Step out reverse
Shift+F9Run and ignore all breakpoint types
Ctrl+F9Run and ignore the last tripped breakpoint type
F10IO Map
F12Load Rom
Ctrl+SSave ROM as
Ctrl+LLoad state
Ctrl+WSave state
Ctrl+GGo to address
Ctrl+AGo to PC
Ctrl+Shift+numbercreate bookmark
Ctrl+numbergo to bookmark
Ctrl+Bgo to previous bookmark or breakpoint
Ctrl+Ngo to next bookmark or breakpoint
Ctrl+Erewind cycles (or scanlines, frames, or seconds)
Ctrl+R or numpad *reset gameboy
Right arrowfollow jump or address dereference
Left arrowundo follow or go to address
Tabtoggle symbols view
Ctrl+Tabgo to next viewer area
Ctrl+Shift+Tabgo to previous viewer area
letter or numberModify code/data
Ctrl+ZUndo modify code/data

expressions, breakpoint conditions, and debug messages

In the "condition" field of a breakpoint, one can enter an expression. for example ($ff44)=$90, to trip on the start of each vblank. the condition will only trip once every time when it becomes true. besides constant values and addresses, one can use the following:

CPU registers: AF, BC, DE, HL, SP, PC, B, C, D, E, H, L, A, ZERO, ZF, Z, CARRY, CY, IME, ALLREGS

These values can also be evaluated by using the menu, "Debug", "Evaluate expression".

In debug messages and expressions, VALUE is the value currently being read or written (useful when logging debug messages on watchpoints)

The unit of all "clocks" values is 1 nop in doublespeed mode, or about 0.5 microseconds. Clocks values are, like all other numerical values, in hexadecimal. The expression "ZEROCLKS" will reset the counter for LASTCLKS. TOTALCLKS is the same value as the clocks counter ("internal divider") in the IO map.

To add "ld d,d" debug messages into the code, assemble an opcode in the form: .msg 'message' where message is the message content. debug messages can contain expressions between %%. When enabled in the settings, whenever a debug message is encountered in the code, it will be logged to the debug messages window or log file.

Debug messages also support ternary operators in the form: "%boolean expression%text if true;text if false;".

The internal code that makes up a debug message is as follows: ld d,d; jr @end; dw $6464; dw $0000; db "message"; @end

One can also create debug messages that point to a null terminated text string elsewhere: ld d,d; jr @end; dw $6464; dw $0001; dw address; dw bank; @end

Commandline parameters

All -params also work as --param. BGB will exit with an exit code of 1 in case of an error, and 0 for normal termination. Sadly, console output is not currently possible (console can't be programmatically enabled or disabled).

Demo recording/playback

There is minimal support for recording and playing back a demo. The support must be considered "experimental", and it may change in the future. It is only intended to be used from the commandline, where the rom to run is also given on the commandline (and not through the menus). One should start from a save state to ensure an exact identical starting state for recording and playback.

The following commandline loads a rom, saves a state, and exits:

bgb -hf -br any -rom -stateonexit game.sna
To record a demo:
bgb -rom game.sna -demorec game.dem
To play back a demo:
bgb -rom game.sna -demoplay game.dem
One can still load a rom directly (without using a save state) but with a risk that the playback differs from the recording.

Demo recording of linked bgb's works, but only on the same machine, not over lan. This is done because it's the only way that both instances will run at the exact same timing, to allow the demo to be played back. To do this, also link listen or connect using commandline parameters (not the menu). Use commandlines such as the following to start the two instances:

bgb -rom red.sna -demorec red.dem -setting winx=300 -listen
bgb -rom blue.sna -demorec blue.dem -setting winx=800 -connect
The demo file format is very simple, with 1 byte per frame for joypad buttons pressed, at the start of each vblank, and before emulation, so it could be handled easily with external tools. If LCD is disabled, no bytes are added to the demo, this was done to keep the demo format deterministic (consistent).

Note: i changed the nibble order around from what it was in 1.5.2, to make it conform to the standard used everywhere: the d-pad should be in the high bits, the other buttons in the low bits. To change existing demo files between the new and old format, use the following command:

bgb -demo152conv filename.dem
If you need it, there is support for the old format. use the parameter -demo152format (in addition to -demoplay or -demorec), but the old format must be considered deprecated.

How to make bgb run faster if you have a slow computer

This should not be necessary on any PC later than ~1998. if you have choppy graphics on a modern PC, the problem is something else.

full screen mode:

select window size -> full screen, to go to a "pseudo full screen" mode (borderless). the GB screen will be at the center of the screen and has the same size which the window had before going to fullscreen mode. "full screen stretched" is a pseudo fullscreen mode where the GB screen covers the whole screen.

real (pageflipped) fullscreen modes are also available in the graphics tab of the settings.

for bgb game link to work at all, you need a modern PC (around 1-2 GHz) and <1ms lag (fast LAN, or localhost). it does not work with all games. on one bgb, you select "listen", on the other you select "connect". it should then show "linked" in the titlebar. there is also an option "remotejoy" so joypad 2 of one bgb controls the other bgb (which does not have keyboard focus, for example).

As of 1.5.2, link in most games should work, and pokemon should work without any glitches (before, pokemon had occasional glitches). one can link between different games, for example pokemon red and blue. Also, a new feature was added: automatic connecting/reconnecting and re-listening: if the link is broken, it will connect or listen again. Also, it will keep trying to connect until it succeeded. This makes the link feature easier to use, and potentially enables unattended use. If the behavior causes problems, it can be disabled in the ini with "LinkAutoListen" and "LinkAutoConnect".

AVI recorder

As of 1.5, one can record to AVI, in addition to recording to BMP screenshots. this allows for greatly improved efficiency while recording, and allow for longer recordings. Sound is still not included in the AVI; enable WAV file writing too, to record sound. The AVI and WAV will have the same filename (and then .avi and .wav), will be perfectly in sync, and can easily be combined in video editing/transcoding software. "media player classic" will automatically use the WAV accompanying the AVI file, allowing for quick preview.

I recommend getting and installing the "camstudio lossless codec". I tested version 1.5. then in bgb, set the codec field to "cscd" to choose the codec. click "Config" to open the configure dialog, and choose "gzip compression" (this will produce smaller AVI files still). Turn off "record half framerate" to record full ~60 fps, which will still not produce too big AVI files, if desired.

The codec can be uploaded as is to youtube, which supports it, or be edited and transcoded to another codec afterwards.

To stitch together multiple recordings (for example if interrupted by the debugger), it is recommended to first combine the video pieces, and the audio pieces, and then mux the audio and video together.

Note for speedrun or "race" use

Speedruns, also known as "races", refer to playing games fast, competitively. Speedrun communities may or may not allow the use of emulators, but if they allow them, requirements may be imposed on them, only some emulators may be allowed, etc.

bgb will, by default, run at the real speed (~59.727 fps). When using bgb for speedruns, and one is not sure whether the settings are default, make sure of the following settings, to ensure running at the real speed:

BGB has a "speedrun mode" which changes a lot of behavior. Restart bgb after changing the speedrun mode setting:
BGB as of 1.5.7 has correct TID (trainer ID) in pokemon games, on GBC and GBA, with and without bootroms.

As of 1.5.8, hard resets (pressing the reset key, * by default), will be recorded and played back in demos. A demo can be recorded during a speedrun, and played back later in non-speedrun mode, as long as all platform settings are the same (choice of platform, GBA, GB player, bootroms), and the BGB version is the same.