Please note this is a custom Marlin firewamre (Bugfix 2.1.x) that I made for my printer
It is currently offered in two flavors. One for the standard size print bed of 235,235,250 and one for an extended print bed of 400,400,500. Please be very careful when installing this firmware as if you install the extended one without a larger bed you can break the printer. You have been warned.
You can find the firmware in the folder Precompiled Firmware
All of the code changes have been documented in each of the folders