boards: st: nucleo_h7s3l8: Add ext_flash_app variant

Add ext_flash_app variant to nucleo_h7s3l8 to allow building
applications running on ext flash.

Based on Erwan Gouriou's work on stm32h7s78_dk in PR #97992
(which is based on A.Jarmouni's work on stm32h750_dk in PR 97037).

Signed-off-by: Thomas Decker <[email protected]>

Author: TD-JBL

boards/st/nucleo_h7s3l8/Kconfig.sysbuild

@@ -0,0 +1,19 @@
+# Copyright (c) 2024-2025 STMicroelectronics
+# Copyright (c) 2025 JB-Lighting Lichtanlagentechnik
+# SPDX-License-Identifier: Apache-2.0
+
+if BOARD_NUCLEO_H7S3L8_STM32H7S3XX_EXT_FLASH_APP
+
+choice BOOTLOADER
+	default BOOTLOADER_MCUBOOT
+endchoice
+
+choice BOOT_SIGNATURE_TYPE
+	default BOOT_SIGNATURE_TYPE_NONE
+endchoice
+
+choice MCUBOOT_MODE
+	default MCUBOOT_MODE_SWAP_USING_OFFSET
+endchoice
+
+endif # BOARD_NUCLEO_H7S3L8_STM32H7S3XX_EXT_FLASH_APP

boards/st/nucleo_h7s3l8/board.cmake

@@ -2,7 +2,7 @@
 
 # keep first
 board_runner_args(stm32cubeprogrammer "--port=swd" "--reset-mode=hw")
-if(CONFIG_XIP AND (CONFIG_STM32_MEMMAP OR CONFIG_BOOTLOADER_MCUBOOT))
+if(CONFIG_STM32_MEMMAP OR CONFIG_BOOTLOADER_MCUBOOT)
   board_runner_args(stm32cubeprogrammer "--extload=MX25UW25645G_NUCLEO-H7S3L8.stldr")
 endif()
 board_runner_args(openocd --target-handle=_CHIPNAME.cpu0)

boards/st/nucleo_h7s3l8/board.yml

@@ -4,3 +4,5 @@ board:
   vendor: st
   socs:
     - name: stm32h7s3xx
+      variants:
+        - name: ext_flash_app

boards/st/nucleo_h7s3l8/doc/index.rst

@@ -213,6 +213,7 @@ the ``--runner`` (or ``-r``) option:
 .. code-block:: console
 
    $ west flash --runner openocd
+   $ west flash --runner jlink
 
 Flashing an application to Nucleo H7S3L8
 ----------------------------------------
@@ -255,7 +256,7 @@ Blinky example can also be used:
    :goals: build flash
 
 Debugging
-=========
+---------
 
 You can debug an application in the usual way.  Here is an example for the
 :zephyr:code-sample:`hello_world` application.
@@ -266,6 +267,112 @@ You can debug an application in the usual way.  Here is an example for the
    :maybe-skip-config:
    :goals: debug
 
+Application in External Flash
+=============================
+
+Because of the limited amount of SoC Flash (64KB), you may want to store the application
+in external OSPI Flash instead, and run it from there. In that case, the MCUboot bootloader
+is needed to chainload the application. A dedicate board variant, ``ext_flash_app``, was created
+for this usecase.
+
+:ref:`sysbuild` makes it possible to build and flash all necessary images needed to run a user application
+from external Flash.
+
+The following example shows how to build :zephyr:code-sample:`hello_world` with Sysbuild enabled:
+
+.. zephyr-app-commands::
+   :tool: west
+   :zephyr-app: samples/hello_world
+   :board: nucleo_h7s3l8/stm32h7s3xx/ext_flash_app
+   :goals: build
+   :west-args: --sysbuild
+
+By default, Sysbuild creates MCUboot and user application images.
+
+Build directory structure created by Sysbuild is different from traditional
+Zephyr build. Output is structured by the domain subdirectories:
+
+.. code-block::
+
+  build/
+  ├── hello_world
+  |    └── zephyr
+  │       ├── zephyr.elf
+  │       ├── zephyr.hex
+  │       ├── zephyr.bin
+  │       ├── zephyr.signed.bin
+  │       └── zephyr.signed.hex
+  ├── mcuboot
+  │    └── zephyr
+  │       ├── zephyr.elf
+  │       ├── zephyr.hex
+  │       └── zephyr.bin
+  └── domains.yaml
+
+.. note::
+
+   With ``--sysbuild`` option, MCUboot will be re-built every time the pristine build is used,
+   but only needs to be flashed once if none of the MCUboot configs are changed.
+
+For more information about the system build please read the :ref:`sysbuild` documentation.
+
+Both MCUboot and user application images can be flashed by running:
+
+.. code-block:: console
+
+   $ west flash
+
+You should see the following message in the serial host program:
+
+.. code-block:: console
+
+   *** Booting MCUboot v2.2.0-224-g0a52195c8181 ***
+   *** Using Zephyr OS build v4.3.0-937-ge0490cf53e03 ***
+   I: Starting bootloader
+   I: Image index: 0, Swap type: none
+   I: Image index: 0, Swap type: none
+   I: Primary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
+   I: Secondary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
+   I: Boot source: none
+   I: Image index: 0, Swap type: none
+   I: Image index: 0, Swap type: none
+   I: Image index: 0, Swap type: none
+   I: Image index: 0, Swap type: none
+   I: Bootloader chainload address offset: 0x0
+   I: Image version: v0.0.0
+   I: Jumping to the first image slot
+   *** Booting Zephyr OS build v4.3.0-937-ge0490cf53e03 ***
+   Hello World! nucleo_h7s3l8/stm32h7s3xx/ext_flash_app
+
+To only flash the user application in the subsequent builds, Use:
+
+.. code-block:: console
+
+   $ west flash --domain hello_world
+
+With the default configuration, the board uses MCUboot's Swap-using-offset mode.
+To get more information about the different MCUboot operating modes and how to
+perform application upgrade, refer to `MCUboot design`_.
+To learn more about how to secure the application images stored in external Flash,
+refer to `MCUboot Encryption`_.
+
+Debugging
+---------
+
+You can debug the application in external flash using ``west`` and ``GDB``.
+
+After flashing MCUboot and the app, execute the following command:
+
+.. code-block:: console
+
+   $ west debugserver
+
+Then, open another terminal (don't forget to activate Zephyr's environment) and execute:
+
+.. code-block:: console
+
+   $ west attach
+
 .. _Nucleo H7S3L8 website:
    https://www.st.com/en/evaluation-tools/nucleo-h7s3l8.html
 
@@ -289,3 +396,9 @@ You can debug an application in the usual way.  Here is an example for the
 
 .. _STM32CubeProgrammer:
    https://www.st.com/en/development-tools/stm32cubeprog.html
+
+.. _MCUboot design:
+   https://docs.mcuboot.com/design.html
+
+.. _MCUboot Encryption:
+   https://docs.mcuboot.com/encrypted_images.html