docs/integration_guide/tfm_integration_guide.rst

#################
Integration guide
#################
The purpose of this document is to provide a guide on how to integrate TF-M
with other hardware platforms and operating systems.

*****************
How to build TF-M
*****************
Follow the :doc:`Build instructions </docs/getting_started/tfm_build_instruction>`.

********************************************************
How to export files for building non-secure applications
********************************************************
Explained in the :doc:`Build instructions </docs/getting_started/tfm_build_instruction>`.

*************************
How to add a new platform
*************************
The hardware platforms currently supported are:

- Soft Macro Model (SMM) Cortex-M33 SSE-200 subsystem for MPS2+ (AN521)
- Cortex-M23 IoT Kit subsystem for MPS2+ (AN519)
- Corstone-300 Ecosystem FVP (Cortex-M55 SSE-300 MPS2+)
- Corstone-300 Ethos-U55 FVP (Cortex-M55 plus Ethos-U55 SSE-300 MPS3)
- Musca-B1 test chip board (Cortex-M33 SSE-200 subsystem)
- Musca-S1 test chip board (Cortex-M33 SSE-200 subsystem)
- CoreLink SSE-200 Subsystem for MPS3 (AN524)
- Corstone SSE-300 with Ethos-U55 Example Subsystem for MPS3 (AN547)
- STM32L5xx: Cortex-M33 based platform (STM32L562 and STM32L552 socs)
- nRF9160 DK (Cortex-M33)
- nRF5340 DK (Cortex-M33 Application MCU)

The files related to the supported platforms are contained under the
``platform`` subfolder. The platform specific files are under
``platform/ext/target``, which is organised by boards
(e.g. ``platform/ext/target/mps2``), while the folder ``platform/ext/common``
is used to store source and header files which are platform generic.

More information about subsystems supported by the MPS2+ board can be found in:
`MPS2+ homepage <https://developer.arm.com/products/system-design/development-boards/fpga-prototyping-boards/mps2>`__

More information about subsystems supported by the MPS3 board can be found in:
`MPS3 homepage <https://developer.arm.com/products/system-design/development-boards/fpga-prototyping-boards/mps3>`__

More information about the Musca-B1 test chip board can be found in:
`Musca-B1 homepage <https://www.arm.com/products/development-tools/development-boards/musca-b1-iot>`__

More information about the Musca-S1 test chip board can be found in:
`Musca-S1 homepage <https://www.arm.com/company/news/2019/05/arm-demonstrates-new-iot-test-chip-and-board>`__

More information about subsystems supported by the MPS3 board can be found in:
`MPS3 homepage <https://www.arm.com/products/development-tools/development-boards/mps3>`__

More information about the Corstone-300 FVPs can be found in:
`Arm Ecosystem FVPs homepage <https://developer.arm.com/tools-and-software/open-source-software/arm-platforms-software/arm-ecosystem-fvps>`__

More information about the STM32L5xx platform can be found in:
`STM32L5 series product page <https://www.st.com/content/st_com/en/products/microcontrollers-microprocessors/stm32-32-bit-arm-cortex-mcus/stm32-ultra-low-power-mcus/stm32l5-series.html>`__

More information about the nRF5340 DK platform can be found in:
`nRF5340 DK product page <https://www.nordicsemi.com/Software-and-tools/Development-Kits/nRF5340-DK>`__

More information about the nRF9160 DK platform can be found in:
`nRF9160 DK product page <https://www.nordicsemi.com/Software-and-tools/Development-Kits/nRF9160-DK>`__

Generic drivers and startup/scatter files
=========================================
The addition of a new platform means the creation of a new subfolder inside
``target/<board_name>`` to provide an implementation of the drivers currently
used by TF-M, in particular MPC, PPC, and USART drivers. In addition to the
drivers, startup and scatter files need to be provided for the supported
toolchains.

There are also board specific drivers which are used by the board
platform to interact with the external world, for example during tests, that
have to be provided, e.g. to blink LEDs or count time in the MPS2 board.

.. Note::

    Currently ITS, PS and BL2 bootloader use different flash interface

Target configuration files
==========================
Inside the base root folder of the selected target, each implementation has to
provide its own copy of ``target_cfg.c/.h``. This file has target specific
configuration functions and settings that are called by the TF-M during the
platform configuration step during TF-M boot. Examples of the configurations
performed during this phase are the MPC configuration, the SAU configuration,
or eventually PPC configuration if supported by the hardware platform.
Similarly, the ``uart_stdout.c`` is used to provide functions needed to redirect
the stdout on UART (this is currently used by TF-M to log messages).

Platform retarget files
=======================
An important part that each new platform has to provide is the set of retarget
files which are contained inside the ``retarget`` folder. These files define the
peripheral base addresses for the platform, both for the secure and non-secure
aliases (when available), and bind those addresses to the base addresses used by
the devices available in the hardware platform.

***************************
How to integrate another OS
***************************

OS migration to Armv8-M platforms
=================================
To work with TF-M on Armv8-M platforms, the OS needs to support the Armv8-M
architecture and, in particular, it needs to be able to run in the non-secure
world. More information about OS migration to the Armv8-M architecture can be
found in the :doc:`OS requirements <os_migration_guide_armv8m>`. Depending upon
the system configuration this may require configuring drivers to use appropriate
address ranges.

Interface with TF-M
===================
The files needed for the interface with TF-M are exported at the
``<install_dir>/interface`` path. The NS side is only allowed to call
TF-M secure functions (veneers) from the NS Thread mode.

TF-M interface header files are exported in ``<install_dir>/interface/include``
directory. For example, the Protected Storage (PS) service PSA API is declared
in the file ``<install_dir>/interface/include/psa/protected_storage.h``.

TF-M also exports a reference implementation of PSA APIs for NS clients in the
``<install_dir>/interface/src``.

On Armv8-M TrustZone based platforms, NS OS shall implement interface API
``tfm_ns_interface_dispatch()`` to integrate with TF-M implementation of PSA
APIs. See ``interface/include/tfm_ns_interface.h`` for the detailed declaration
of ``tfm_ns_interface_dispatch()``.
TF-M provides an example of ``tfm_ns_interface_dispatch()`` implementation on
Armv8-M TrustZone based platforms. In this example, NS OS calls mutex in
``tfm_ns_interface_dispatch()`` to synchronize multiple NS client calls to TF-M.
See ``interface/src/tfm_ns_interface.c.example`` for more details.

TF-M provides a reference implementation of NS mailbox on multi-core platforms,
under folder ``interface/src/multi_core``.
See :doc:`Mailbox design </docs/technical_references/dual-cpu/mailbox_design_on_dual_core_system>`
for TF-M multi-core mailbox design.

Interface with non-secure world regression tests
================================================
A non-secure application that wants to run the non-secure regression tests
needs to call the ``tfm_non_secure_client_run_tests()``. This function is
exported into the header file ``test_framework_integ_test.h`` inside the
``<build_dir>/install`` folder structure in the test specific files,
i.e. ``<build_dir>/install/export/tfm/test/inc``. The non-secure regression
tests are precompiled and delivered as a static library which is available in
``<build_dir>/install/export/tfm/test/lib``, so that the non-secure application
needs to link against the library to be able to invoke the
``tfm_non_secure_client_run_tests()`` function. The PS non-secure side
regression tests rely on some OS functionality e.g. threads, mutexes etc. These
functions comply with CMSIS RTOS2 standard and have been exported as thin
wrappers defined in ``os_wrapper.h`` contained in
``<build_dir>/install/export/tfm/test/inc``. OS needs to provide the
implementation of these wrappers to be able to run the tests.

NS client Identification
========================
See
:doc:`ns client identification documentation </docs/technical_references/tfm_ns_client_identification>`.

*********************
Non-secure interrupts
*********************
Non-secure interrupts are allowed to preempt Secure thread mode.
With the current implementation, a NSPE task can spoof the identity of another
NSPE task. This is an issue only when NSPE has provisions for task isolation.
Note, that ``AIRCR.PRIS`` is still set to restrict the priority range available
to NS interrupts to the lower half of available priorities so that it wouldn't
be possible for any non-secure interrupt to preempt a higher-priority secure
interrupt.

**********************************
Integration with non-Cmake systems
**********************************

Generated Files
===============

Files that are derived from PSA manifests are generated at build-time by cmake.
For integration with systems that do no use cmake, the files must be generated
manually.

The ``tools/tfm_parse_manifest_list.py`` script can be invoked manually. Some
arguments will be needed to be provided. Please refer to
``tfm_parse_manifest_list.py --help`` for more details.

Some variables are used in the template files, these will need to be set in the
environment before the script will succeed when the script is not run via cmake.

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