-- Update February 2021 --
While this still works, I consider it obsolete and advise against installing it. I noticed an annoying screen tearing / scrolling lag issue that makes this Retropie setup not fun to play. If you want to use the Banana Pi as a retro gaming machine, please use my build of Lakka for the Banana Pi instead, see the links below.
Forum thread: https://forums.libretro.com/t/lakka-image-for-banana-pi-m1/32244
Download link: https://drive.google.com/drive/folders/1tjoKSu9DAnC-2eplAUqDt2wnqSZ_ZDs0
-- Original --
Scripts for installing Retropie on Banana Pi M1 (Allwinner A20)
Here are the instructions how to configure the system and build RetroPie for yourself: https://github.com/bernhard263/Bananapi-Retropie/wiki
Here is a ready-made SD card image for the Banana Pi that has everything already installed: https://github.com/bernhard263/Bananapi-Retropie/wiki/Image