1 Article Purpose[edit]

This section details the process used to build TF-A from sources and to deploy it on your target.
The build example is based on the OpenSTLinux environment:

  • Developer Package
  • Distribution Package

2 Overview[edit]

TF-A is the FSBL for the ST trusted boot chain. It must be configured or updated depending on your platform.

Cross compilation of TF-A is only required if it is to be modified. By default, in the Starter Package, the TF-A image is named: tf-<board>-trusted.stm32.
In changes are made, you must rebuild TF-A and update all the FSBL partitions of your boot device with this new image. A second FSBL image is used as a backup image.

The build process creates a full STM32 image that can be used for Flash integrating a specific header.
This trusted firmware-A image contains a device tree, a BL2 and a BL32 stage.
These binaries are built in a single step during the build process.


3 Developer Package[edit]

3.1 Install sources[edit]

The Developer Package contains OpenSTLinux and TF-A sources: TF-A Installation

3.2 Official source tree[edit]

Warning.png The STM32MP1 platform is not yet fully upstreamed. So features are not available from this repository

Download source code from the official github

 PC $> git clone

3.3 Build Process[edit]

3.3.1 Initialise the cross compile environment[edit]

Setup Cross compile environment

3.3.2 TF-A Build flags[edit]

Mandatory flags:

  • ARM_ARCH_MAJOR=7: the major version of ARM Architecture to target (STM32MP15 is ARMv7 architecture based)
  • ARCH=aarch32: specify aarch32 architecture to be built
  • PLAT=stm32mp1: builds an stm32mp1 platform
  • DTB_FILE_NAME=<fdt file name>.dtb: this must be defined to build the proper target and include the correct DTB file into the final file

Optional flags:

  • AARCH32_SP=sp_min: builds the BL32 secure monitor if required
  • AARCH32_SP=optee: do not include BL32 and prepare BL2 for optee-specific load
  • DEBUG=1: add debug information in all binaries
  • V=1: print verbose compilation traces

3.4 Build command[edit]

From the Developer Package tarball, a Makefile.sdk is present and must be used to build the target. It automatically sets the proper configuration for the TF-A build.

 PC $> make -f Makefile.sdk TF_A_CONFIG=trusted TFA_DEVICETREE=stm32mp157c-<board>

The latest version of the helper file is also available in this user guide: README.HOW_TO.txt.

Warning.png The DTB_FILE_NAME flag must be set to select the correct board configuration.

The device tree file for the target must be located in fdts folder (stm32mp157c-<board>.dts)

If no Makefile.sdk exists, you must add your own environment flags:

 PC $> unset LDFLAGS;
 PC $> unset CFLAGS;
 PC $> make ARM_ARCH_MAJOR=7 ARCH=aarch32 PLAT=stm32mp1 AARCH32_SP=sp_min DTB_FILE_NAME=stm32mp157c-<board>.dtb

3.5 Final image[edit]

Final image is available for Flash or SD card update in the corresponding folder:


4 Distribution Package[edit]

For an OpenSTLinux distribution, the TF-A image is built in release mode by default. The yocto recipe can be found in:


If you want to modify the TF-A code source, use the following steps starting from an already downloaded and built OpenSTLinux distribution.

4.1 Access sources[edit]

You can use devtool to access the source.

 PC $> cd <baseline root directory>
 PC $> devtool modify tf-a-stm32mp sources/boot/tf-a

By going to the sources/boot/tf-a folder, you can manage and modify the TF-A sources. To rebuild it, go back to the build-<distribution> folder and launch the TF-A recipe:

 PC $> bitbake tf-a-stm32mp

The final image is deployed in the image default output folder.

5 Update software on board[edit]

5.1 Partitioning of binaries[edit]

The TF-A build provides a binary named tf-a-stm32mp157c-<board>.stm32 that MUST be copied to a dedicated partition named "fsblX" (X depends of needed backup).

Warning.png TF-A must be located in the first partition of your boot device.

You can just update the first partition for a simple test, but all backup partitions must contain the same image at the end.

5.2 Update via SDCARD[edit]

If you use an SD card, you can simply update TF-A using the dd command on your host.
Plug your SD card into the computer and copy the binary to the dedicated partition; on an SDCard/USB disk the "fsbl1" partition is partition 1:

 - SDCARD: /dev/mmcblkXp1 (where X is the instance number)
 - SDCARD via USB reader: /dev/sdX1 (where X is the instance number)
  • Linux
 PC $> dd if=<tf-a file> of=/dev/<device partition> bs=1M conv=fdatasync
Info.png To find the partition associated to a specific label, just plug the

SDCARD/USB disk into your PC and call the following command:

 PC $> ls -l /dev/disk/by-partlabel/
 total 0
 lrwxrwxrwx 1 root root 10 Jan 17 17:38 bootfs -> ../../mmcblk0p4
 lrwxrwxrwx 1 root root 10 Jan 17 17:38 fsbl1 -> ../../mmcblk0p1          ➔ FSBL1 (TF-A)
 lrwxrwxrwx 1 root root 10 Jan 17 17:38 fsbl2 -> ../../mmcblk0p2          ➔ FSBL2 (TF-A backup – same content as FSBL)
 lrwxrwxrwx 1 root root 10 Jan 17 17:38 rootfs -> ../../mmcblk0p5
 lrwxrwxrwx 1 root root 10 Jan 17 17:38 ssbl -> ../../mmcblk0p3           ➔ SSBL (U-Boot)
 lrwxrwxrwx 1 root root 10 Jan 17 17:38 userfs -> ../../mmcblk0p6
  • Windows

There is an existing dd for Windows that makes binary copying possible.

5.3 Update via USB mass storage on U-boot[edit]

See How to use USB mass storage in U-Boot

Follow the previous section to put tf-a-<board>.stm32 onto SDCard/USB disk

5.4 Update your boot device (including SD card on the target)[edit]

Refer to the STM32CubeProgrammer documentation to update your target.