===== RetroFun! USB-to-DB9 adapter by E4U =====
    * https://www.ebay.com/itm/232825859958

===== RetroFun! Twin USB-to-DB9 adapter by E4U =====
    * https://www.ebay.com/itm/RetroFun-Twin-Connect-2x-Retro-joysticks-to-PC-Pegasus-Sega-Atari-Commdore/232825843831

Files storage (updater, configurator, instructions etc):
    * https://drive.google.com/drive/folders/1liT12FRtot6ySOGx6-XNP2GA-ugKfOXf
RETROFUN Joystick Adapters (DB9) INTERFACE MANUAL (PDF)
    * [[https://gurce.net/c64mini/_media/retrofun_joystickadapters_db9_-manual.pdf|retrofun_joystickadapters_db9_-manual.pdf]]
Firmware upgrading procedure (official video)
    * https://youtu.be/V9Ds2-qgEjg
RetroFun Twin C64Mini testing both joystick ports (official video)
    * https://youtu.be/X2fwb47jppY
Related thread at TheC64 Community forum:
    * http://thec64community.online/thread/202/retrofun-db9-joystick-adapter-working
Old information page:
    * http://electronica4u.com/