STM32U5A9 boot fail at low temperatures

[NPato]

Hi,

We have a design that at normal temperatures runs fine (21C). If it goes below 0C it starts failing to boot.

The system has the Secure Boot Secure Firmware Update (SBSFU) system on it. We found that putting a delay at the start of the main() function in bl2_main.c seems to allow it to run. The delay needs to be about half a second.

Then as we reduce the temperature towards -40C we find we need to increase the delay to over a second to get it to work.

Does this sound familiar to anyone? Any ideas what could be going on?

Thanks

Nigel

[Uwe Bonnes]

Do your crystals/oscillators have slow startup times?

[Andrew Neil]

Probably an external hardware issue; eg, clocks (as @Uwe Bonnes said), power supply, reset ...