Method of use:
• Power-on the system as defined in RM0456.
• Reset the STM32U585xx as defined in RM0456.
• “Running” non‑secure application generates a reset (ArmV8 reset instruction or operation).
Parameters:
• Not applicable
Actions:
• Execute code located at the fixed secure entry point (SECBOOTADD0 address) defined for the TOE as
described in UM2851. TOE is configured to locate the immutable TFM_SBSFU_Boot application at the
secure fix entry point. The TFM_SBSFU_Boot application executes first the Secure Boot function and then
the Secure Firmware Update function. The Secure Boot function manages the secure initialization of the
platform and the Secure Firmware Update checks in the secure image secondary and non
‑
secure image
secondary slots if there are any candidate images to be analyzed.
Errors:
• STM32U585xx option bytes values violation: In case STM32U585xx option bytes values are not correctly
configured to ensure TOE security, the TOE secure boot procedure detects the problem and blocks the TOE
secure boot procedure execution (Reset is generated, except for the case of RDP option bytes value for
which infinite loop is executed in the secure domain).
Secure image secondary slot interface
The Secure image secondary slot is used to implement the remote firmware update functionality of the secure
image by triggering the bootloader image upgrade process. It is a memory area where a new candidate of the
secure image is placed by writing into it, using the non‑secure application either via a physical interface or either
via a wireless interface or using the standalone external loader application via a physical interface. After any
product reset, if magic 16 bytes are present at slot area end location, the TOE attempts to interpret the data as a
candidate image and applies it to the secure image primary slot in case it is correctly verified. If a candidate image
is analyzed as not valid (authenticity and integrity) then image data are deleted from the secure image secondary
slot.
UM2852
Operational guidance for the integrator role
UM2852 - Rev 1
page 15/27
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