~/src/Firmware. To build the firmware for RDDRONE-FMUK66 (NXPhlite), open a terminal in this folder (On Windows, follow steps 1. and 2. at https://dev.px4.io/en/setup/dev_env_windows_cygwin.html#getting_started), and use the following command:
nxp_fmuk66-v3_default.px4, which can be found at
~/src/Firmware/build/nxp_fmuk66-v3_default. This is the firmware file based on the current master, which can already by uploaded to the RDDRONE-FMUK66 using QGroundControl. It will also create a
nxp_fmuk66-v3.binfile in the same location which you can program with the debugger.