Why does it matter if stm32wb5x_FUS_fw.bin is flashed before stm32wb5x_BLE_Stack_full_fw.bin?

[MWojc.2]

I'm trying to use Zephyr for development on the nucleo_wb55rg board. While doing this I noticed the problem described in:

https://github.com/zephyrproject-rtos/zephyr/issues/27348

I think that the sequence firmware flash writes matters. 

Writing stm32wb5x_FUS_fw.bin and then stm32wb5x_BLE_Stack_full_fw.bin works. But not the other way around.

Could someone tell me why the order of writes is important?

[Remi QUINTIN]

​The recommended (release notes) programming addresses for FUS and RF FW matter as one is erased after programming (FUS) while the other (RF FW) is not.

Moreover, the FUS should be updated only once per version. Do not try to upgrade the FUS with the same version as the one currently present.