Boards: STM32H750B-DK: Introduce App in Ext Flash variant #97037

JarmouniA · 2025-10-06T07:25:29Z

Introduce a board variant for storing an app in external QSPI NOR Flash and chainloading it with MCUboot (which is placed in internal Flash) to be executed in place (XiP) (MCUBOOT_MODE_DIRECT_XIP, set by default in board's Kconfig.sysbuild).

The ext Flash memory partition also allows for using the Swap-using-offset & swap-using-move MCUboot image upgrade algorithms, eventhough it's not optimal as it has same-sized slots.

The new variant requires a board DT overlay on the MCUboot side (mcu-tools/mcuboot#2479) to set the internal Flash & Flash controller as the chosen 'zephyr,flash' & 'zephyr,flash-controller'. This way, no overlay will be needed at the Zephyr user app level.

west build -p always -b stm32h750b_dk/stm32h750xx/ext_flash_app samples/modules/lvgl/demos --sysbuild

erwango

@JarmouniA I was wondering if snippets could be used instead of adding a target each time we need to introduce an ext_mem app. Did you look at this possibility ?
Just thinking out loud, maybe the combination with sysbuild doesn't work great.

JarmouniA · 2025-10-06T10:25:55Z

@JarmouniA I was wondering if snippets could be used

Not sure what we would put in them, maybe an ext Flash-specific snippet, but then the internal Flash is not necessarily the same, its sector size...

github-actions · 2025-10-06T21:20:14Z

The following west manifest projects have changed revision in this Pull Request:

Name	Old Revision	New Revision	Diff
mcuboot	mcu-tools/mcuboot@`d5b0dcb`	mcu-tools/mcuboot#2479	mcu-tools/mcuboot#2479/files

Additional metadata changed:

Name	URL	Submodules	West cmds	`module.yml`	Blobs
mcuboot	✏

⛔ DNM label due to: 1 project with PR revision and 1 project with metadata changes

Note: This message is automatically posted and updated by the Manifest GitHub Action.

erwango

Nice!

Though, I think we can get rid of the mcuboot overlay by using stm32h750b_dk as the mcuboot target. This way, mcuboot is a usual zephyr application running on internal flash.
(Note also that zephyr,code-partition = &boot_partition; is already defined in mcuboot app.overlay)

To do this, you probably need to add a sysbuild.cmake file to the board, stating:

if(SB_CONFIG_BOOTLOADER_MCUBOOT)
  set_target_properties(mcuboot PROPERTIES BOARD stm32h750b_dk/stm32h750xx)
endif()

and no mcuboot dependency anymore.

Can you have a try and report back (somehow I can't find any stm32h750b_dk here anymore to test it myself) ?

JarmouniA · 2025-10-07T14:21:27Z

Though, I think we can get rid of the mcuboot overlay by using stm32h750b_dk as the mcuboot target. This way, mcuboot is a usual zephyr application running on internal flash. (Note also that zephyr,code-partition = &boot_partition; is already defined in mcuboot app.overlay)

I already thought of that, but the MCUboot App build depends on info specified in ext_flash_app variant dts, an example is info about the slots
https://github.com/mcu-tools/mcuboot/blob/17a6ecd279d631abfd865bfa041d40964f9ecc62/boot/zephyr/CMakeLists.txt#L500
https://github.com/mcu-tools/mcuboot/blob/17a6ecd279d631abfd865bfa041d40964f9ecc62/boot/zephyr/include/target.h#L39

There are potentially other interdependencies at the sysbuild level as well, I don't think it's a good idea to use different targets.

erwango · 2025-10-07T14:40:11Z

There are potentially other interdependencies at the sysbuild level as well, I don't think it's a good idea to use different targets.

It builds on my side. I'm just unable to test it.
Defining all partitions in a unique .dtsi file is already what we're doing for stm32n6570_dk, this shouldn't be an issue on h7 target. Do I miss something ?

JarmouniA · 2025-10-07T14:57:34Z

It builds on my side. I'm just unable to test it. Defining all partitions in a unique .dtsi file is already what we're doing for stm32n6570_dk, this shouldn't be an issue on h7 target. Do I miss something ?

The MCUboot partitions (slot0, slot1...) are not relevant to the base variant, which is supposed to be used with a regular Zephyr app (MCUboot is not a regular app, it's a bootloader) in internal Flash & external Flash is used for storage or whatever,

zephyr/boards/st/stm32h750b_dk/stm32h750b_dk.dts

Line 34 in b26dafd

reg = <0x00000000 DT_SIZE_M(128)>; /* 128MB */

So why would we put the MCUboot partitions in the common dtsi, and of what use would be the ext_flash_app variant in that case?

erwango · 2025-10-08T09:22:16Z

The MCUboot partitions (slot0, slot1...) are not relevant to the base variant, which is supposed to be used with a regular Zephyr app (MCUboot is not a regular app, it's a bootloader) in internal Flash & external Flash is used for storage or whatever,

We already have this case on other boards where "main" variant .dts provides slot0/slot1 on internal flash and this "main" variant could be used either as a "direct" zephyr application or chainloaded behind mcuboot.

Difference here is that we need a variant to be able to specify different zephyr,flash and zephyr,flash-controller, hence the need for a dedicated variant (ext_flash_app). With your proposal, we don't need to provide a .conf file anymore for the MCUBoot target, let's go one step further and get rid of the .overlay and dependency on MCUBoot completely.

Also note that these boards (based on h750, h7r/s) are a bit specific in the way that they have a quite limited internal flash and are meant to be used with a ext_flash, from which the main application should run.
Having the main variant running on internal flash is convenient in order to be able to run upstream zephyr samples and tests, but proposing the external flash as an extra large storage slot is only interesting for validation purpose, not as a real final app. If co-existence of this storage slot with slot0/slot1 partition on the main variant raises an issue, then it should be defined as an overlay in tests/samples that actually need it.

Last point about interest of the ext_flash_app variant is that it could be used to specify configurations that would not be supported on the main variant running on the internal flash (thinking about video use cases for instance). But I need to verify this point.

JarmouniA · 2025-10-08T09:40:24Z

but proposing the external flash as an extra large storage slot is only interesting for validation purpose, not as a real final app

It could definitely be used that way in a product where app upgrade is not needed by just relocating the big/non-critical parts of the app, running from internal Flash, to ext Flash.

JarmouniA · 2025-10-08T09:56:24Z

boards/st/stm32h750b_dk/stm32h750b_dk_stm32h750xx_ext_flash_app.dts

+			#address-cells = <1>;
+			#size-cells = <1>;
+
+			slot0_partition: partition@0 {


This does not work in RAM_LOAD mode, build system considers the slot address as the user app's hex address (where image will be flashed), which is actually at an offset of 0x90000000.

zephyr/cmake/mcuboot.cmake

Line 151 in 8c13c07

set(imgtool_args ${imgtool_args} --hex-addr ${slot0_partition_address})

Did you try with CONFIG_XIP=n ? (required when RAM_LOAD is used)

It's done by sysbuild

zephyr/share/sysbuild/image_configurations/MAIN_image_default.cmake

Line 40 in 8c13c07

set_config_bool(${ZCMAKE_APPLICATION} CONFIG_XIP n)

Will be fixed by #97413

erwango · 2025-10-14T13:36:04Z

It could definitely be used that way in a product where app upgrade is not needed by just relocating the big/non-critical parts of the app, running from internal Flash, to ext Flash.

So actually, I've found another reason to keep your proposal is that whatever we propose for ext flash should also be compatible with use of chainloaded application from internal flash (when it applies, ie on SoC with internal flash big enough to support this case). Ie, we should support the following:

Zephyr running on internal flash: Default target (board.dts)
Zephyr running on internal flash launched by MCUBoot: Default target (board.dts) + sysbuild
Zephyr running on external flash launched by MCUBoot: Ext flash target (board_foo_ext_flash_app.dts) + sysbuild

So my proposal wouldn't work.
This being said, I'm still willing to avoid this dependency on MCUBoot for a boilerplate config.

Pull in the necessary MCUboot bits, will be removed before merging the PR. Signed-off-by: Abderrahmane JARMOUNI <[email protected]>

Introduce a board variant for storing an app in external QSPI NOR Flash and chainloading it with MCUboot (placed in internal Flash) to be executed in place (XiP) (set by default, MCUBOOT_MODE_DIRECT_XIP). The new variant requires a board DT overlay on the MCUboot side to set the internal Flash & Flash controller as the chosen 'zephyr,flash' & 'zephyr,flash-controller'. Signed-off-by: Abderrahmane JARMOUNI <[email protected]>

Add stm32h750b_dk/stm32h750xx/ext_flash_app target to CI platforms Signed-off-by: Abderrahmane JARMOUNI <[email protected]>

Add stm32h750b_dk/stm32h750xx/ext_flash_app target to CI platforms. Signed-off-by: Abderrahmane JARMOUNI <[email protected]>

sonarqubecloud · 2025-10-14T17:47:35Z

Please retry analysis of this Pull-Request directly on SonarQube Cloud

This was referenced Oct 6, 2025

Boot: Zephyr: Boards: Fix STM32H750B-DK App in Ext Flash support mcu-tools/mcuboot#2479

Open

STM32 OSPI NOR: run application from external flash memory #93032

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erwango reviewed Oct 6, 2025

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JarmouniA force-pushed the fix_h750b-dk_ext_flash_app branch from 95ac7ff to 573417e Compare October 6, 2025 21:19

github-actions bot added manifest manifest-mcuboot DNM (manifest) This PR should not be merged (controlled by action-manifest) labels Oct 6, 2025

JarmouniA force-pushed the fix_h750b-dk_ext_flash_app branch 2 times, most recently from 00106a2 to b26dafd Compare October 6, 2025 21:34

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zephyrbot added area: Samples Samples area: Sysbuild area: Tests Issues related to a particular existing or missing test area: MCUBoot area: Devicetree Bindings area: Bootloader area: Boards/SoCs platform: STM32 ST Micro STM32 area: Flash labels Oct 7, 2025

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JarmouniA commented Oct 8, 2025

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JarmouniA force-pushed the fix_h750b-dk_ext_flash_app branch from b26dafd to 00e6e32 Compare October 12, 2025 19:09

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tpambor mentioned this pull request Oct 12, 2025

Flash partitions layout changed for stm32h573i_dk #97423

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JarmouniA force-pushed the fix_h750b-dk_ext_flash_app branch from 1b338a1 to 7d7cc0d Compare October 12, 2025 21:16

erwango added this to the v4.3.0 milestone Oct 14, 2025

JarmouniA force-pushed the fix_h750b-dk_ext_flash_app branch from 7d7cc0d to 7be53c6 Compare October 14, 2025 17:19

JarmouniA added 4 commits October 14, 2025 19:19

manifest: pull in the necessary MCUboot bits

e2d22a4

Pull in the necessary MCUboot bits, will be removed before merging the PR. Signed-off-by: Abderrahmane JARMOUNI <[email protected]>

samples: sysbuild: with_mcuboot: add stm32h750b_dk to CI platforms

a789cae

Add stm32h750b_dk/stm32h750xx/ext_flash_app target to CI platforms Signed-off-by: Abderrahmane JARMOUNI <[email protected]>

tests: boot: test_mcuboot: add stm32h750b_dk to CI platforms

0cf7d9d

Add stm32h750b_dk/stm32h750xx/ext_flash_app target to CI platforms. Signed-off-by: Abderrahmane JARMOUNI <[email protected]>

JarmouniA force-pushed the fix_h750b-dk_ext_flash_app branch from 7be53c6 to 0cf7d9d Compare October 14, 2025 17:19

zephyrbot added the area: File System label Oct 14, 2025

Boards: STM32H750B-DK: Introduce App in Ext Flash variant #97037

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