Because I needed to insert nuts in my prints and therefore G-code instructions in their file, I upgraded my printer firmware to Marlin as in here :
At the beginning I did used to get the 6 beeps when booting, and was able to boot back to the initial firmware when hiding the
upgrade.cbd file in a folder, instead of the root level of the SD card.
But I did by mistake load/save some settings to the EEPROM I guess, and I cannot get back to the initial firmware - at boot time there isn't any beep anymore and it boots directly on the marlin boot wallpaper.
How to prevent Marlin forcing the 3D printer to boot on it please?