>> >> The target HW was STM32F407ZG. I built my own NuttX toolchain for it. > > How? Could you write a bit more?
In the early days, Greg modified buildroot to build a GNU toolchain specifically for NuttX (include files included). I wanted a toolchain that used the hard-float ABI for Armv7E-M. I maintained it (unofficially) for some time submitting patches (up to gcc 8.3, gdb 7.5 IIRC). I’m not sure what happened the the buildroot tree after Apache adoption.
