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Building Retro-Go

Prerequisites

You will need a working installation of esp-idf. Versions 4.2 to 5.2 are supported.

Note: As of retro-go 1.35, I use 4.3. Version 4.1 was used for 1.20 to 1.34 versions.

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.

Obtaining the code

Using git is the preferred method but you can also download a zip from the project's front page and extract it if you want, Retro-Go has no external dependencies.

There are generally two active git branches on retro-go:

  • master contains the code form the most recent release and is usually tested and known to be working
  • dev contains code in development that will be merged to master upon the next release and is often untested

git clone -b <branch> https://github.com/ducalex/retro-go/

Build everything and generate .fw:

  • Generate a .fw file to be installed with odroid-go-firmware (SD Card):
    ./rg_tool.py build-fw or ./rg_tool.py release (clean build)
  • Generate a .img to be flashed with esptool.py (Serial):
    ./rg_tool.py build-img or ./rg_tool.py release (clean build)

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

  1. ./rg_tool.py build-fw launcher prboom-go

Note that the app named retro-core contains the following emulators: NES, PCE, G&W, Lynx, and SMS/GG/COL. As such, these emulators cannot be selected individually. The reason for the bundling is simply size, together they account for a mere 700KB instead of almost 3MB when they were built separately.

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:

  1. Flash: ./rg_tool.py --port=COM3 flash prboom-go
  2. Monitor: ./rg_tool.py --port=COM3 monitor prboom-go
  3. Flash then monitor: ./rg_tool.py --port=COM3 run prboom-go

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_BAUD represents --baud
  • RG_TOOL_PORT represents --port

Windows

Running ./rg_tool.py ... on Windows might invoke the wrong Python interpreter (causing the build to fail) or even do nothing at all. In such cases you should use python rg_tool.py ... instead.

Changing the launcher's images

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

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.

To resolve the backtrace you will need the application's elf file. If lost, you can recreate it by building the app again using the same esp-idf and retro-go versions. Then you can run xtensa-esp32-elf-addr2line -ifCe app-name/build/app-name.elf.

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 handy-go)

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!