STM32F767 HSE setup timing out on custom board (using mbed os 6)

[LLawr.1]

Hello,

I have been testing a custom board using the STM32F767ZI/VI for the last two weeks, and most things have been going well. I ran into an issue using CAN on the VI for some reason so I decided to switch to the ZI, and things were working well until I realized that it was not using the 8MHz HSE, but the 16MHz HSI instead because of the process of elimination it goes through to select a clock. After forcing it to use the HSE, mbed os crashes, saying SetSysClock failed. I believe the HSE setup is timing out, because I increased the timeout value from 100ms to 5000ms, and now it just takes 5 seconds to crash instead of right away. The crystal (NX3225GD-8MHZ-STD-CRA-3) is connected close to the chip with two 4.3pF load capacitors. This was copied from the NUCLEO-F767ZI board. Any ideas as to why this might be happening? Any help is greatly appreciated, especially seeing as how I'm on a time limit. Thanks!

[Bowman32]

Hello @LLawr.1​ 

Did the HSE fail to startup? Can you check the HSERDY flag in RCC clock control register (RCC_CR)?

Try to reduce the external capacitors and see what happen.

For more details about oscillator PCB guidelines and external capacitors. You can refer to application note AN2867 "Oscillator design guide for STM8AF/AL/S, STM32 MCUs and MPUs".

Bouraoui