STM32U5 TF-M flash layout clarifications.

[ROMAINPC]

Hello,\ I am studying the size of the Non-Secure flash memory on an STM32U5 with Trusted Firmware M enable. Reference documentation is UM2851.\ According to this ST documentation there are several flash layouts depending on the secure update mode. (1 swap mode, and 4 others overwrite modes : single image and/or single slot mode).\ The documentation also explains the role of the integrator to enlarge the Non-Secure partition. It is recommended to start from the b_u585i_iot02a project.

There are flash_layout.h and region_defs.h, however the flash_layout.h doesn't match the documentation. 8KB data slots are not mentioned. Above all, the default size of Secure and Non-Secure partitions does not correspond to any layout. This is why I have several questions:

• How to be sure that my Zephyr project is using swap mode with dual images mode? How enable other modes?
• Which flash_layout.h to use? Particularly if I want to maintain security trust.
• How do I know how far I can enlarge the size of Non-Secure partitions? Is there a behavior to expect if the NS partition is too large?

This issue follows this one on the RAM usage.

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