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open_agb_firm

open_agb_firm is a bare metal interface for natively running GBA games and homebrew using the 3DS's built-in GBA hardware.

open_agb_firm is also a complete and better alternative to GBA VC injects (AGB_FIRM), allowing for:

• Launching GBA files directly from the SD card
• Writing save files directly to the SD card
• Automatic save type configuration using an included database
• User configuration, such as gamma settings
• And more to come!

Disclaimer

open_agb_firm is currently in alpha. While open_agb_firm is relatively stable and safe to use, some quirks that have not been fixed. See Known Issues for more information.

Additionally, we are not responsible for any damage that may occur to your system as a direct or indirect result of you using open_agb_firm.

Setup

• Download the latest release and extract it.
• Copy the open_agb_firm.firm file to your 3DS's SD card at /luma/payloads if you're using Luma3DS or elsewhere if you're using fastboot3DS.
• Copy the 3ds folder to the root of your 3DS's SD card. Merge folders if asked.
• Launch open_agb_firm using Luma3DS by holding START while booting your 3DS or assign it to a slot if you're using fastboot3DS.
• After open_agb_firm launches, use the file browser to navigate to a .gba ROM to run.

Controls

A/B/L/R/START/SELECT - GBA buttons, respectively

SELECT+Y - Dump screen output to /3ds/open_agb_firm/texture_dump.bmp

• If the screen output freezes, press HOME to fix it. This is a hard to track down bug that will be fixed.

Hold the power button to turn off the 3DS.

Configuration

Settings are stored in /3ds/open_agb_firm/config.ini.

General

General settings.

u8 backlight - Backlight brightness

• Default: 64
• Possible values:
  • Old 3DS: 20-117
  • New 3DS: 16-142
• Values ≤64 are recommended.

bool directBoot - Skip GBA BIOS intro at game startup

• Default: false

bool useGbaDb - Use gba_db.bin to get save types

• Default: true

Video

Video-related settings.

u8 scaler - Video scaler. 0 = none, 1 = bilinear, 2 = hardware.

• Default: 2

float gbaGamma - GBA input gamma

• Default: 2.2

float lcdGamma - Output LCD gamma

• Default : 1.54

float contrast - Screen gain

• Default: 1.0

float brightness - Screen lift

• Default: 0.0

Game

Game-specific settings. Only intended to be used in the per-game settings (romName.ini in /3ds/open_agb_firm/saves).

u8 saveSlot - Savegame slot (0-9)

• Default: 0

Advanced

Options for advanced users. No pun intended.

bool saveOverride - Open save type override menu after selecting a game

• Default: false

u16 defaultSave - Change save type default when save type is not in gba_db.bin and cannot be autodetected

• Default: 14 (SRAM 256k)
• Possible values:
  • 0, 1: EEPROM 8k
  • 2, 3: EEPROM 64k
  • 4, 6, 8: Flash 512k RTC
  • 5, 7, 9: Flash 512k
  • 10, 12: Flash 1m RTC
  • 11, 13: Flash 1m
  • 14: SRAM 256k
  • 15: None

Known Issues

This section is reserved for a listing of known issues. At present only this remains:

• Sleep mode is not fully implemented.
• Using SELECT+Y to dump screen output to a file can freeze the screen output sometimes.
• Save type autodetection may still fail for certain games using EEPROM.
• Lack of settings (including brightness control during gameplay).
• No cheats and other enhancements.

If you happen to stumble over another bug, please open an issue or contact profi200 via other platforms.

Hardware Limitations

open_agb_firm using the 3DS's built-in GBA hardware. Unfortunately, this comes with limitations compared to GBA emulators. This is a list of limitations we can't solve in software or are very hard to work around.

• >32 MiB (>256 Mbit) games and homebrew.
• Games with extra hardware built into the cartridge (except real-time clocks). Patches are required.
• Proper save autodetection (can't find save type during gameplay).
• GBA serial port (aka Link Cable).
• >32 KiB (>256 Kbit) SRAM (homebrew games/emulators).
• Reboots are required for switching between games.
• No save states. Very difficult to implement because no direct hardware access.
• Sound has lots of aliasing issues. No known workaround (hardware bug).

EEPROM Fixer

Most emulators output EEPROM saves differently than what open_agb_firm expects, making them incompatible. Fortunately, they are very easy to fix, using this tool by exelotl.

The tool also works vise versa, if you want to use a save generated by open_agb_firm with an emulator.

FAQ

Q: Why isn't open_agb_firm a normal 3DS app?
A: To access the 3DS's GBA hardware, open_agb_firm needs to run with full hardware access, which can only be provided by running as a FIRM.

Q: Is this safe to use?
A: Of course! While open_agb_firm does run with full hardware access, a lot of work has been put in by several people to ensure that nothing unexpected happens. Some backend code from open_agb_firm is actually used in fastboot3ds!

Q: What games work with open_agb_firm?
A: In theory, all of them, except those that fall within the hardware limitations.

Q: How can I increase the brightness?
A: Increase the value of the backlight setting in config.ini. See Configuration for more information.

Q: Why do the colors look off?
A: The default gamma settings are intended to make up for the washed out colors the 3DS LCD has. If they look weird to you, setting the outGamma setting to 2.2 might help.

Q: Why do some of my ROM hacks/homebrew games have saving issues?
A: open_agb_firm resorts to save autodetection when it can't find an entry for the game it's running in gba_db.bin (which only contains data for official games), and it's a bit wonky for games that use EEPROM or misleading SDK save strings.

Q: Why doesn't my save file from an emulator work?
A: There's a good chance that the save you're having issues with is an EEPROM save, which most emulators output differently. See EEPROM Fixer.

Q: My game doesn't save properly!
A: First, please ensure that the GBA ROM you are playing is not modified in any way, and matches its No-Intro checksums. Second, make sure you aren't using an existing .SAV file, because some may have issues for various reasons. Third, make sure your gba_db.bin is up-to-date. If everything seems to be in order but the game still doesn't save properly, please open an issue so it can be fixed. In the meantime, the useGbaDb and saveOverride settings may be useful (see Configuration for more information).

Compiling

To compile open_agb_firm, the following needs to be installed:

• devkitARM
• Corelink DMA-330 Assembler
• CTR Firm Builder or firmtool

Additionally, p7zip (or if available, p7zip-full) needs to be installed to make release builds. Also, make sure that the dma330as and firm_builder/firmtool binaries are in the PATH environment variable and accessible to the Makefile.

Build open_agb_firm as a debug build via make, or as a release build via make release.

License

You may use this under the terms of the GNU General Public License GPL v3 or the terms of any later revisions of the GPL. Refer to the provided LICENSE.txt file for further information.

Thanks to...

• yellows8
• plutoo
• smea
• Normmatt
• WinterMute
• ctrulib devs
• LumaTeam
• devkitPro
• ChaN (fatfs)
• benhoyt (inih)
• fastboot3DS project
• MAME
• No-Intro
• Wolfvak, Sono and all the other people in #GodMode9 on freenode/Discord
• endrift, Extrems and all the other people in #mgba on freenode
• ...everyone who contributed to 3dbrew.org

Copyright (C) 2021 derrek, profi200, d0k3