USB Flashing Format (UF2) UF2 is a file format, developed by Microsoft for PXT (also known as Microsoft MakeCode), that is particularly suitable for flashing microcontrollers over MSC (Mass Storage Class; aka removable flash drive). For a more friendly explanation, check out this blog post. Also, take a look at the list of implementations at the bottom of this document. Overview The UF2 file consists of 512 byte blocks, each of which is self-contained and independent of others. Each 512 byte block consists of (see below for details): magic numbers at the beginning and at the end address where the data should be flashed