Nucleo board stuck when starting without USB connection

[Jelurol]

Hello,

I am using a Nucleo F446RE board, and I have developped a small program that works fine as long as the board is connected to the PC with the USB cable.

Once the program has been tested, I have removed the USB cable and used E5V external power supply.

When I start the power supply, LD1 flashes red (waiting for USB), and nothing happens (stuck!).

If at that point I connect the USB it works ok.

Also, if I press the reset button, it also works ok.

Obviously, the system by default is waiting for a USB connection that will never come...

Is there a way to avoid that problem ?

Thanks for any help !

[PaulbXYZ]

I had this symptom on a Nucleo-L432 board. I tried other oscillator settings and a delay after SystemClock_Config() (as suggested in another thread) without any success. I found that the ST-LINK MCU was pulling the NRST line low, although it was officially unpowered. It was probably being back-powered from the target MCU. I removed the jumper from T_NRST to NRST (SB9) and that solved it. I am still able to program the target MCU using the ST-LINK MCU; it must not need control of NRST.