You are right. I used your changes and build using -u and I still have the same issue (the board does not bootup). This is what I can see on the serial port: ADE
This is debug output from arch/arm/src/stm32h7/start.c. The hang occurs somewhere after line 412 ( showprogress('E');), and probably after nx_start() is called. I would put breakpoints on nx_start(), up_initialize(), and nsh_main().
