17.5.5 NVM Boot Sequence

The ROM code performs the initialization and valid code detection for the external memories as described below only if those memories are not disabled in the Boot Configuration word.

The NVM bootloader program first initializes the PIOs related to the NVM device. Then it configures the right peripheral depending on the NVM and tries to access this memory. If the initialization fails, it restores the reset values for the PIO and the peripheral, and then tries to fulfill the same operations on the next NVM of the sequence.

If the initialization is successful, the NVM bootloader program reads the beginning of the NVM and determines if the NVM contains a valid code.

If the NVM does not contain a valid code, the NVM bootloader program restores the reset value for the peripherals and then tries to fulfill the same operations on the next NVM of the sequence.

If a valid code is found, this code is loaded from the NVM into the internal SRAM and executed by branching at address 0x0000_0000 after remap. This code may be the application code or a second-level bootloader. All the calls to functions are PC-relative and do not use absolute addresses.