Description

Retro-Go is a firmware to play retro games on ESP32-based devices (officially supported are ODROID-GO and MRGC-G32). The project consists of a launcher and half a dozen applications that have been heavily optimized to reduce their cpu, memory, and flash needs without reducing compatibility!

Supported systems:

Nintendo: NES, Gameboy, Gameboy Color, SNES (very slow)
Sega: Master System, SG-1000, Game Gear
Coleco: Colecovision
NEC: PC Engine
Atari: Lynx
Others: DOOM (including mods!)

Retro-Go features:

In-game menu
Favorites and recently played
GB color palettes, RTC adjust and save
NES color palettes, PAL roms, NSF support
More emulators, applications
Scaling and filtering options
Better performance and compatibility
Turbo Speed/Fast forward
Customizable launcher
Cover art and save state previews
exFAT support
And more!

Screenshots

Game covers

Game covers should be placed in the romart folder at the base of your sd card. You can obtain a pre-made pack from this repository or from the release page. Retro-Go is also compatible with the older Go-Play romart pack.

Adding covers

The preferred cover art format is PNG with a resolution of max 160x168 and I recommend post-processing your PNG with pngquant or imagemagick's -colors 255 for smaller file sizes.

You can use one of two naming schemes:

Using the CRC32 (press A -> Properties in the launcher to find it). Assuming a CRC of ABCDE123, the cover file will be /romart/nes/A/ABCDE123.png.
Using the rom file name. Assuming a rom named myrom.nes, the cover file will be /romart/nes/myrom.nes.png (notice the inclusion of the rom extension).

Problems and solutions

Black screen / Boot loops

Retro-Go typically detects and resolves application crashes and freezes automatically. However, if you do get stuck in a boot loop, you can hold DOWN while powering up the device to return to the launcher.

CRC32... is annoying!

Let your device sit idle for a while, it will scan your files preemptively. Alternatively you can disable cover display in the options menu.

Display update mode

The maximum fill rate of the LCD is ~30fps. To work around that limitation, retro-go implements a partial update mode that refreshes only the portions of the screen that have changed. This process works very well at reducing tearing and improving animations smoothness. However if you notice glitches or stuttering you can try setting Update: Full in the options.

Sound quality

The volume isn't correctly attenuated on the GO, resulting in upper volume levels that are too loud and lower levels that are distorted due to DAC resolution. A quick way to improve the audio is to cut one of the speaker wire and add a 15 Ohm (or thereabout) resistor in series. Soldering is better but not required, twisting the wires tightly will work just fine. A more involved solution can be seen here.

Game Boy SRAM (aka Save/Battery/Backup RAM)

In Retro-Go, save states will provide you with the best and most reliable save experience. That being said, please read on if you need or want SRAM saves. The SRAM format is compatible with VisualBoyAdvance so it may be used to import or export saves.

On real hardware, Game Boy games save their state to a battery-backed SRAM chip in the cartridge. A typical emulator on the deskop would save the SRAM to disk periodically or when leaving the emulator, and reload it when you restart the game. This isn't possible on the Odroid-GO because we can't detect when the device is about to be powered down and we can't save too often because it causes stuttering. That is why the auto save delay is configurable (disabled by default) and pausing the emulation (opening a menu) will also save to disk if needed. The SRAM file is then reloaded on startup (unless a save state loading was requested via "Resume").

Other issues

An up to date list of incompatible/broken games can be found on the ODROID-GO forum. This is also the place to submit bug reports and feature requests.

BIOS files

Some emulators support loading a BIOS. The files should be placed as follows:

GB: /retro-go/system/gb_bios.bin
GBC: /retro-go/system/gbc_bios.bin
FDS: /retro-go/system/fds_bios.bin

Future plans / Feature requests

Cheats support (In progress)
Famicom Disk System (In progress)
SGB enhanced palette support (In progress)
Netplay (Stalled)
Multiple save states
More emulators (Atari 2600/5200/7800, Neo Geo Pocket, Arduboy)
WiFi file manager
Chip sound player
Sleep mode

Building Retro-Go

Prerequisites

You will need a working installation of esp-idf 4.0.x or 4.1.x and only the CMake (default) build system is supported.

Note: Versions 4.2 and 4.3 will also work but there are unresolved performance issues at this time.

ESP-IDF Patches

Patching esp-idf may be required for full functionality. Patches are located in tools/patches and can be applied to your global esp-idf installation, they will not break your other projects/devices.

sdcard-fix: This patch is mandatory for the ODROID-GO (and clones).
panic-hook: This is to help users report bugs, see Capturing crash logs below for more details. The patch is optional but recommended.
enable-exfat: Enable exFAT support. I don't recommended it but it works if you need it.

Build everything and generate .fw:

rg_tool.py build-fw or rg_tool.py release (clean build)

For a smaller build you can also specify which apps you want, for example the launcher + nes + gameboy only:

rg_tool.py build-fw launcher nofrendo-go gnuboy-go

Build, flash, and monitor individual apps for faster development:

It would be tedious to build, move to SD, and flash a full .fw all the time during development. Instead you can:

Flash: rg_tool.py --port=COM3 --offset=0x100000 flash nofrendo-go
Monitor: rg_tool.py --port=COM3 monitor nofrendo-go
Flash then monitor: rg_tool.py --port=COM3 --offset=0x100000 run nofrendo-go

Note: You will need to know where retro-go is located on your device. Typically it is 0x100000 for the ODROID-GO and 0x50000 for the MRGC-G32. You can confirm that by searching the serial output for the line launcher OTA app 00 10 00100000 00050000 where 100000 is the offset in hex.

Environment variables

rg_tool.py supports a few environment variables if you want to avoid passing flags all the time:

RG_TOOL_TARGET represents --target
RG_TOOL_OFFSET represents --offset
RG_TOOL_BAUD represents --baud
RG_TOOL_PORT represents --port

Changing the launcher's images

All images used by the launcher (headers, logos) are located in launcher/images. If you edit them you must run the launcher/gen_images.py script to regenerate images.c. Magenta (rgb(255, 0, 255) / 0xF81F) is used as the transparency colour.

Changing or adding fonts

Fonts are found in components/retro-go/fonts. There are basic instructions in fonts.h on how to add fonts. In short you need to generate a font.c file and add it to fonts.h. It'll try to add better instructions soon...

Capturing crash logs

When a panic occurs, Retro-Go has the ability to save debugging information to /sd/crash.log. This provides users with a simple way of recovering a backtrace (and often more) without having to install drivers and serial console software. A weak hook is installed into esp-idf panic's putchar, allowing us to save each chars in RTC RAM. Then, after the system resets, we can move that data to the sd card. You will find a small esp-idf patch to enable this feature in tools/patches.

Porting

I don't want to maintain non-ESP32 ports in this repository but let me know if I can make small changes to make your own port easier! The absolute minimum requirements for Retro-Go are roughly:

Processor: 200Mhz 32bit little-endian
Memory: 2MB
Compiler: C99 and C++03 (for lynx and snes)

Whilst all applications were heavily modified or even redesigned for our constrained needs, special care is taken to keep Retro-Go and ESP32-specific code exclusively in their port file (main.c). This makes reusing them in your own codebase very easy!

Acknowledgements

The design of the launcher was inspired (copied) from pelle7's go-emu.
The NES/GBC/SMS emulators and base library were originally from the "Triforce" fork of the official Go-Play firmware by crashoverride, Nemo1984, and many others.
PCE-GO is a fork of HuExpress and pelle7's port was used as reference.
The Lynx emulator is a port of libretro-handy.
The SNES emulator is a port of Snes9x 1.60.
The DOOM engine is a port of PrBoom 2.5.0.
PNG support is provided by lodepng.
PCE cover art is from Christian_Haitian.
Some icons from Rokey.
Background images from es-theme-gbz35.
Special thanks to RGHandhelds and MyRetroGamecase for sending me a G32 device.

License

Everything in this project is licensed under the GPLv2 license with the exception of the following components:

components/retro-go (Retro-Go's framework, zlib)
handy-go/components/handy (Lynx emulator, zlib)

License

ladyada/retro-go

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