STM32F767ZI on external power supply is stuck until reset button is pressed

[MMaro.2]

Hi everyone,

I have developed a software using mbed OS on a Nucleo-144 board (STM32F767ZI), and everything works well.

Now, I am powering my board from an external power supply, and I moved the JP3 jumper to VIN position.

However, the board is stuck. The program correctly starts only if:

• the board is connected to the PC through a USB
• the reset button is pressed

I read several posts, and I tried all the proposed solutions: update the ST-Link firmware, place a jumper between the NRST and 3V3 pins, also removed the SB111 0-ohm resistance between NRST and RST, but nothing works.

One interesting thing I have is this: if I manage to start the program (using USB connection or reset button), powering off and on again the board in a very short amount of time make the nucleo works fine. However, if I power it off and wait a few seconds, then the board is stuck again until the reset button is pressed or USB connection provided.

Any help on this?

Thank you very much.

[z0ki]

this solved the problem for me:

https://community.st.com/t5/stm32-mcus-boards-and-hardware/nucleo-f767zi-external-power-start-up-problem/m-p/714804#M21087

here in short:

PROBLEM:

The clock for the STM32 is provided by the on board debugger. This clock signal is generated about 2 seconds after the board is power, after which a reset takes effect. By default HSE Startup Timout Value is 100ms, so it timeouts before the clock is available → the board doesn’t start.

that solves it:

1. If you don't care to much of startup time increase timeout for the HSE to wait for MCO (RCC -> Parameter Settings -> HSE Startup Timout Value (ms))
2. use the internal clock HSI (if you don’t need accurate clock)
3. use external oscillator (X3, HSE) - soldering needed

thanks to Elec in the OG post on stack overflow and Rubb to extend it.