docs/getting_started/user-guide.rst

User Guide
==========

This document describes how to build Trusted Firmware-A (TF-A) and run it with a
tested set of other software components using defined configurations on the Juno
Arm development platform and Arm Fixed Virtual Platform (FVP) models. It is
possible to use other software components, configurations and platforms but that
is outside the scope of this document.

This document assumes that the reader has previous experience running a fully
bootable Linux software stack on Juno or FVP using the prebuilt binaries and
filesystems provided by Linaro. Further information may be found in the
`Linaro instructions`_. It also assumes that the user understands the role of
the different software components required to boot a Linux system:

-  Specific firmware images required by the platform (e.g. SCP firmware on Juno)
-  Normal world bootloader (e.g. UEFI or U-Boot)
-  Device tree
-  Linux kernel image
-  Root filesystem

This document also assumes that the user is familiar with the `FVP models`_ and
the different command line options available to launch the model.

This document should be used in conjunction with the `Firmware Design`_.

Host machine requirements
-------------------------

The minimum recommended machine specification for building the software and
running the FVP models is a dual-core processor running at 2GHz with 12GB of
RAM. For best performance, use a machine with a quad-core processor running at
2.6GHz with 16GB of RAM.

The software has been tested on Ubuntu 16.04 LTS (64-bit). Packages used for
building the software were installed from that distribution unless otherwise
specified.

The software has also been built on Windows 7 Enterprise SP1, using CMD.EXE,
Cygwin, and Msys (MinGW) shells, using version 5.3.1 of the GNU toolchain.

Tools
-----

Install the required packages to build TF-A with the following command:

.. code:: shell

    sudo apt-get install device-tree-compiler build-essential gcc make git libssl-dev

Download and install the AArch32 (arm-eabi) or AArch64 little-endian
(aarch64-linux-gnu) GCC 8.3-2019.03 cross compiler from `Arm Developer page`_.

Optionally, TF-A can be built using clang version 4.0 or newer or Arm
Compiler 6. See instructions below on how to switch the default compiler.

In addition, the following optional packages and tools may be needed:

-  ``device-tree-compiler`` (dtc) package if you need to rebuild the Flattened Device
   Tree (FDT) source files (``.dts`` files) provided with this software. The
   version of dtc must be 1.4.6 or above.

-  For debugging, Arm `Development Studio 5 (DS-5)`_.

-  To create and modify the diagram files included in the documentation, `Dia`_.
   This tool can be found in most Linux distributions. Inkscape is needed to
   generate the actual \*.png files.

TF-A has been tested with pre-built binaries and file systems from
`Linaro Release 19.06`_. Alternatively, you can build the binaries from
source using instructions provided at the `Arm Platforms User guide`_.

Getting the TF-A source code
----------------------------

Clone the repository from the Gerrit server. The project details may be found
on the `arm-trusted-firmware-a project page`_. We recommend the "`Clone with
commit-msg hook`" clone method, which will setup the git commit hook that
automatically generates and inserts appropriate `Change-Id:` lines in your
commit messages.

Checking source code style
~~~~~~~~~~~~~~~~~~~~~~~~~~

Trusted Firmware follows the `Linux Coding Style`_ . When making changes to the
source, for submission to the project, the source must be in compliance with
this style guide.

Additional, project-specific guidelines are defined in the `Trusted Firmware-A
Coding Guidelines`_ document.

To assist with coding style compliance, the project Makefile contains two
targets which both utilise the `checkpatch.pl` script that ships with the Linux
source tree. The project also defines certain *checkpatch* options in the
``.checkpatch.conf`` file in the top-level directory.

.. note::
   Checkpatch errors will gate upstream merging of pull requests.
   Checkpatch warnings will not gate merging but should be reviewed and fixed if
   possible.

To check the entire source tree, you must first download copies of
``checkpatch.pl``, ``spelling.txt`` and ``const_structs.checkpatch`` available
in the `Linux master tree`_ *scripts* directory, then set the ``CHECKPATCH``
environment variable to point to ``checkpatch.pl`` (with the other 2 files in
the same directory) and build the `checkcodebase` target:

.. code:: shell

    make CHECKPATCH=<path-to-linux>/linux/scripts/checkpatch.pl checkcodebase

To just check the style on the files that differ between your local branch and
the remote master, use:

.. code:: shell

    make CHECKPATCH=<path-to-linux>/linux/scripts/checkpatch.pl checkpatch

If you wish to check your patch against something other than the remote master,
set the ``BASE_COMMIT`` variable to your desired branch. By default, ``BASE_COMMIT``
is set to ``origin/master``.

Building TF-A
-------------

-  Before building TF-A, the environment variable ``CROSS_COMPILE`` must point
   to the cross compiler.

   For AArch64:

   .. code:: shell

       export CROSS_COMPILE=<path-to-aarch64-gcc>/bin/aarch64-linux-gnu-

   For AArch32:

   .. code:: shell

       export CROSS_COMPILE=<path-to-aarch32-gcc>/bin/arm-eabi-

   It is possible to build TF-A using Clang or Arm Compiler 6. To do so
   ``CC`` needs to point to the clang or armclang binary, which will
   also select the clang or armclang assembler. Be aware that the
   GNU linker is used by default.  In case of being needed the linker
   can be overridden using the ``LD`` variable. Clang linker version 6 is
   known to work with TF-A.

   In both cases ``CROSS_COMPILE`` should be set as described above.

   Arm Compiler 6 will be selected when the base name of the path assigned
   to ``CC`` matches the string 'armclang'.

   For AArch64 using Arm Compiler 6:

   .. code:: shell

       export CROSS_COMPILE=<path-to-aarch64-gcc>/bin/aarch64-linux-gnu-
       make CC=<path-to-armclang>/bin/armclang PLAT=<platform> all

   Clang will be selected when the base name of the path assigned to ``CC``
   contains the string 'clang'. This is to allow both clang and clang-X.Y
   to work.

   For AArch64 using clang:

   .. code:: shell

       export CROSS_COMPILE=<path-to-aarch64-gcc>/bin/aarch64-linux-gnu-
       make CC=<path-to-clang>/bin/clang PLAT=<platform> all

-  Change to the root directory of the TF-A source tree and build.

   For AArch64:

   .. code:: shell

       make PLAT=<platform> all

   For AArch32:

   .. code:: shell

       make PLAT=<platform> ARCH=aarch32 AARCH32_SP=sp_min all

   Notes:

   -  If ``PLAT`` is not specified, ``fvp`` is assumed by default. See the
      `Summary of build options`_ for more information on available build
      options.

   -  (AArch32 only) Currently only ``PLAT=fvp`` is supported.

   -  (AArch32 only) ``AARCH32_SP`` is the AArch32 EL3 Runtime Software and it
      corresponds to the BL32 image. A minimal ``AARCH32_SP``, sp_min, is
      provided by TF-A to demonstrate how PSCI Library can be integrated with
      an AArch32 EL3 Runtime Software. Some AArch32 EL3 Runtime Software may
      include other runtime services, for example Trusted OS services. A guide
      to integrate PSCI library with AArch32 EL3 Runtime Software can be found
      `here`_.

   -  (AArch64 only) The TSP (Test Secure Payload), corresponding to the BL32
      image, is not compiled in by default. Refer to the
      `Building the Test Secure Payload`_ section below.

   -  By default this produces a release version of the build. To produce a
      debug version instead, refer to the "Debugging options" section below.

   -  The build process creates products in a ``build`` directory tree, building
      the objects and binaries for each boot loader stage in separate
      sub-directories. The following boot loader binary files are created
      from the corresponding ELF files:

      -  ``build/<platform>/<build-type>/bl1.bin``
      -  ``build/<platform>/<build-type>/bl2.bin``
      -  ``build/<platform>/<build-type>/bl31.bin`` (AArch64 only)
      -  ``build/<platform>/<build-type>/bl32.bin`` (mandatory for AArch32)

      where ``<platform>`` is the name of the chosen platform and ``<build-type>``
      is either ``debug`` or ``release``. The actual number of images might differ
      depending on the platform.

-  Build products for a specific build variant can be removed using:

   .. code:: shell

       make DEBUG=<D> PLAT=<platform> clean

   ... where ``<D>`` is ``0`` or ``1``, as specified when building.

   The build tree can be removed completely using:

   .. code:: shell

       make realclean

Summary of build options
~~~~~~~~~~~~~~~~~~~~~~~~

The TF-A build system supports the following build options. Unless mentioned
otherwise, these options are expected to be specified at the build command
line and are not to be modified in any component makefiles. Note that the
build system doesn't track dependency for build options. Therefore, if any of
the build options are changed from a previous build, a clean build must be
performed.

Common build options
^^^^^^^^^^^^^^^^^^^^

-  ``AARCH32_INSTRUCTION_SET``: Choose the AArch32 instruction set that the
   compiler should use. Valid values are T32 and A32. It defaults to T32 due to
   code having a smaller resulting size.

-  ``AARCH32_SP`` : Choose the AArch32 Secure Payload component to be built as
   as the BL32 image when ``ARCH=aarch32``. The value should be the path to the
   directory containing the SP source, relative to the ``bl32/``; the directory
   is expected to contain a makefile called ``<aarch32_sp-value>.mk``.

-  ``ARCH`` : Choose the target build architecture for TF-A. It can take either
   ``aarch64`` or ``aarch32`` as values. By default, it is defined to
   ``aarch64``.

-  ``ARM_ARCH_MAJOR``: The major version of Arm Architecture to target when
   compiling TF-A. Its value must be numeric, and defaults to 8 . See also,
   *Armv8 Architecture Extensions* and *Armv7 Architecture Extensions* in
   `Firmware Design`_.

-  ``ARM_ARCH_MINOR``: The minor version of Arm Architecture to target when
   compiling TF-A. Its value must be a numeric, and defaults to 0. See also,
   *Armv8 Architecture Extensions* in `Firmware Design`_.

-  ``BL2``: This is an optional build option which specifies the path to BL2
   image for the ``fip`` target. In this case, the BL2 in the TF-A will not be
   built.

-  ``BL2U``: This is an optional build option which specifies the path to
   BL2U image. In this case, the BL2U in TF-A will not be built.

-  ``BL2_AT_EL3``: This is an optional build option that enables the use of
   BL2 at EL3 execution level.

-  ``BL2_IN_XIP_MEM``: In some use-cases BL2 will be stored in eXecute In Place
   (XIP) memory, like BL1. In these use-cases, it is necessary to initialize
   the RW sections in RAM, while leaving the RO sections in place. This option
   enable this use-case. For now, this option is only supported when BL2_AT_EL3
   is set to '1'.

-  ``BL2_INV_DCACHE``: This is an optional build option which control dcache
   invalidation upon BL2 entry. Some platform cannot handle cache operations
   during entry as the coherency unit is not yet initialized. This may cause
   crashing. Leaving this option to '1' (default) will allow the operation.
   This option is only relevant when BL2_AT_EL3 is set to '1'.

-  ``BL31``: This is an optional build option which specifies the path to
   BL31 image for the ``fip`` target. In this case, the BL31 in TF-A will not
   be built.

-  ``BL31_KEY``: This option is used when ``GENERATE_COT=1``. It specifies the
   file that contains the BL31 private key in PEM format. If ``SAVE_KEYS=1``,
   this file name will be used to save the key.

-  ``BL32``: This is an optional build option which specifies the path to
   BL32 image for the ``fip`` target. In this case, the BL32 in TF-A will not
   be built.

-  ``BL32_EXTRA1``: This is an optional build option which specifies the path to
   Trusted OS Extra1 image for the  ``fip`` target.

-  ``BL32_EXTRA2``: This is an optional build option which specifies the path to
   Trusted OS Extra2 image for the ``fip`` target.

-  ``BL32_KEY``: This option is used when ``GENERATE_COT=1``. It specifies the
   file that contains the BL32 private key in PEM format. If ``SAVE_KEYS=1``,
   this file name will be used to save the key.

-  ``BL33``: Path to BL33 image in the host file system. This is mandatory for
   ``fip`` target in case TF-A BL2 is used.

-  ``BL33_KEY``: This option is used when ``GENERATE_COT=1``. It specifies the
   file that contains the BL33 private key in PEM format. If ``SAVE_KEYS=1``,
   this file name will be used to save the key.

-  ``BRANCH_PROTECTION``: Numeric value to enable ARMv8.3 Pointer Authentication
   and ARMv8.5 Branch Target Identification support for TF-A BL images themselves.
   If enabled, it is needed to use a compiler (e.g GCC 9.1 and later versions) that
   supports the option ``-mbranch-protection``.
   Selects the branch protection features to use:
-  0: Default value turns off all types of branch protection
-  1: Enables all types of branch protection features
-  2: Return address signing to its standard level
-  3: Extend the signing to include leaf functions

   The table below summarizes ``BRANCH_PROTECTION`` values, GCC compilation options
   and resulting PAuth/BTI features.

   +-------+--------------+-------+-----+
   | Value |  GCC option  | PAuth | BTI |
   +=======+==============+=======+=====+
   |   0   |     none     |   N   |  N  |
   +-------+--------------+-------+-----+
   |   1   |   standard   |   Y   |  Y  |
   +-------+--------------+-------+-----+
   |   2   |   pac-ret    |   Y   |  N  |
   +-------+--------------+-------+-----+
   |   3   | pac-ret+leaf |   Y   |  N  |
   +-------+--------------+-------+-----+

   This option defaults to 0 and this is an experimental feature.
   Note that Pointer Authentication is enabled for Non-secure world
   irrespective of the value of this option if the CPU supports it.

-  ``BUILD_MESSAGE_TIMESTAMP``: String used to identify the time and date of the
   compilation of each build. It must be set to a C string (including quotes
   where applicable). Defaults to a string that contains the time and date of
   the compilation.

-  ``BUILD_STRING``: Input string for VERSION_STRING, which allows the TF-A
   build to be uniquely identified. Defaults to the current git commit id.

-  ``CFLAGS``: Extra user options appended on the compiler's command line in
   addition to the options set by the build system.

-  ``COLD_BOOT_SINGLE_CPU``: This option indicates whether the platform may
   release several CPUs out of reset. It can take either 0 (several CPUs may be
   brought up) or 1 (only one CPU will ever be brought up during cold reset).
   Default is 0. If the platform always brings up a single CPU, there is no
   need to distinguish between primary and secondary CPUs and the boot path can
   be optimised. The ``plat_is_my_cpu_primary()`` and
   ``plat_secondary_cold_boot_setup()`` platform porting interfaces do not need
   to be implemented in this case.

-  ``CRASH_REPORTING``: A non-zero value enables a console dump of processor
   register state when an unexpected exception occurs during execution of
   BL31. This option defaults to the value of ``DEBUG`` - i.e. by default
   this is only enabled for a debug build of the firmware.

-  ``CREATE_KEYS``: This option is used when ``GENERATE_COT=1``. It tells the
   certificate generation tool to create new keys in case no valid keys are
   present or specified. Allowed options are '0' or '1'. Default is '1'.

-  ``CTX_INCLUDE_AARCH32_REGS`` : Boolean option that, when set to 1, will cause
   the AArch32 system registers to be included when saving and restoring the
   CPU context. The option must be set to 0 for AArch64-only platforms (that
   is on hardware that does not implement AArch32, or at least not at EL1 and
   higher ELs). Default value is 1.

-  ``CTX_INCLUDE_FPREGS``: Boolean option that, when set to 1, will cause the FP
   registers to be included when saving and restoring the CPU context. Default
   is 0.

-  ``CTX_INCLUDE_MTE_REGS``: Enables register saving/reloading support for
   ARMv8.5 Memory Tagging Extension. A value of 0 will disable
   saving/reloading and restrict the use of MTE to the normal world if the
   CPU has support, while a value of 1 enables the saving/reloading, allowing
   the use of MTE in both the secure and non-secure worlds. Default is 0
   (disabled) and this feature is experimental.

-  ``CTX_INCLUDE_PAUTH_REGS``: Boolean option that, when set to 1, enables
   Pointer Authentication for Secure world. This will cause the ARMv8.3-PAuth
   registers to be included when saving and restoring the CPU context as
   part of world switch. Default value is 0 and this is an experimental feature.
   Note that Pointer Authentication is enabled for Non-secure world irrespective
   of the value of this flag if the CPU supports it.

-  ``DEBUG``: Chooses between a debug and release build. It can take either 0
   (release) or 1 (debug) as values. 0 is the default.

-  ``DISABLE_BIN_GENERATION``: Boolean option to disable the generation
   of the binary image. If set to 1, then only the ELF image is built.
   0 is the default.

-  ``DYN_DISABLE_AUTH``: Provides the capability to dynamically disable Trusted
   Board Boot authentication at runtime. This option is meant to be enabled only
   for development platforms. ``TRUSTED_BOARD_BOOT`` flag must be set if this
   flag has to be enabled. 0 is the default.

-  ``E``: Boolean option to make warnings into errors. Default is 1.

-  ``EL3_PAYLOAD_BASE``: This option enables booting an EL3 payload instead of
   the normal boot flow. It must specify the entry point address of the EL3
   payload. Please refer to the "Booting an EL3 payload" section for more
   details.

-  ``ENABLE_AMU``: Boolean option to enable Activity Monitor Unit extensions.
   This is an optional architectural feature available on v8.4 onwards. Some
   v8.2 implementations also implement an AMU and this option can be used to
   enable this feature on those systems as well. Default is 0.

-  ``ENABLE_ASSERTIONS``: This option controls whether or not calls to ``assert()``
   are compiled out. For debug builds, this option defaults to 1, and calls to
   ``assert()`` are left in place. For release builds, this option defaults to 0
   and calls to ``assert()`` function are compiled out. This option can be set
   independently of ``DEBUG``. It can also be used to hide any auxiliary code
   that is only required for the assertion and does not fit in the assertion
   itself.

-  ``ENABLE_BACKTRACE``: This option controls whether to enables backtrace
   dumps or not. It is supported in both AArch64 and AArch32. However, in
   AArch32 the format of the frame records are not defined in the AAPCS and they
   are defined by the implementation. This implementation of backtrace only
   supports the format used by GCC when T32 interworking is disabled. For this
   reason enabling this option in AArch32 will force the compiler to only
   generate A32 code. This option is enabled by default only in AArch64 debug
   builds, but this behaviour can be overridden in each platform's Makefile or
   in the build command line.

-  ``ENABLE_MPAM_FOR_LOWER_ELS``: Boolean option to enable lower ELs to use MPAM
   feature. MPAM is an optional Armv8.4 extension that enables various memory
   system components and resources to define partitions; software running at
   various ELs can assign themselves to desired partition to control their
   performance aspects.

   When this option is set to ``1``, EL3 allows lower ELs to access their own
   MPAM registers without trapping into EL3. This option doesn't make use of
   partitioning in EL3, however. Platform initialisation code should configure
   and use partitions in EL3 as required. This option defaults to ``0``.

-  ``ENABLE_PIE``: Boolean option to enable Position Independent Executable(PIE)
   support within generic code in TF-A. This option is currently only supported
   in BL31. Default is 0.

-  ``ENABLE_PMF``: Boolean option to enable support for optional Performance
   Measurement Framework(PMF). Default is 0.

-  ``ENABLE_PSCI_STAT``: Boolean option to enable support for optional PSCI
   functions ``PSCI_STAT_RESIDENCY`` and ``PSCI_STAT_COUNT``. Default is 0.
   In the absence of an alternate stat collection backend, ``ENABLE_PMF`` must
   be enabled. If ``ENABLE_PMF`` is set, the residency statistics are tracked in
   software.

-  ``ENABLE_RUNTIME_INSTRUMENTATION``: Boolean option to enable runtime
   instrumentation which injects timestamp collection points into TF-A to
   allow runtime performance to be measured. Currently, only PSCI is
   instrumented. Enabling this option enables the ``ENABLE_PMF`` build option
   as well. Default is 0.

-  ``ENABLE_SPE_FOR_LOWER_ELS`` : Boolean option to enable Statistical Profiling
   extensions. This is an optional architectural feature for AArch64.
   The default is 1 but is automatically disabled when the target architecture
   is AArch32.

-  ``ENABLE_SPM`` : Boolean option to enable the Secure Partition Manager (SPM).
   Refer to the `Secure Partition Manager Design guide`_ for more details about
   this feature. Default is 0.

-  ``ENABLE_SVE_FOR_NS``: Boolean option to enable Scalable Vector Extension
   (SVE) for the Non-secure world only. SVE is an optional architectural feature
   for AArch64. Note that when SVE is enabled for the Non-secure world, access
   to SIMD and floating-point functionality from the Secure world is disabled.
   This is to avoid corruption of the Non-secure world data in the Z-registers
   which are aliased by the SIMD and FP registers. The build option is not
   compatible with the ``CTX_INCLUDE_FPREGS`` build option, and will raise an
   assert on platforms where SVE is implemented and ``ENABLE_SVE_FOR_NS`` set to
   1. The default is 1 but is automatically disabled when the target
   architecture is AArch32.

-  ``ENABLE_STACK_PROTECTOR``: String option to enable the stack protection
   checks in GCC. Allowed values are "all", "strong", "default" and "none". The
   default value is set to "none". "strong" is the recommended stack protection
   level if this feature is desired. "none" disables the stack protection. For
   all values other than "none", the ``plat_get_stack_protector_canary()``
   platform hook needs to be implemented. The value is passed as the last
   component of the option ``-fstack-protector-$ENABLE_STACK_PROTECTOR``.

-  ``ERROR_DEPRECATED``: This option decides whether to treat the usage of
   deprecated platform APIs, helper functions or drivers within Trusted
   Firmware as error. It can take the value 1 (flag the use of deprecated
   APIs as error) or 0. The default is 0.

-  ``EL3_EXCEPTION_HANDLING``: When set to ``1``, enable handling of exceptions
   targeted at EL3. When set ``0`` (default), no exceptions are expected or
   handled at EL3, and a panic will result. This is supported only for AArch64
   builds.

-  ``FAULT_INJECTION_SUPPORT``: ARMv8.4 extensions introduced support for fault
   injection from lower ELs, and this build option enables lower ELs to use
   Error Records accessed via System Registers to inject faults. This is
   applicable only to AArch64 builds.

   This feature is intended for testing purposes only, and is advisable to keep
   disabled for production images.

-  ``FIP_NAME``: This is an optional build option which specifies the FIP
   filename for the ``fip`` target. Default is ``fip.bin``.

-  ``FWU_FIP_NAME``: This is an optional build option which specifies the FWU
   FIP filename for the ``fwu_fip`` target. Default is ``fwu_fip.bin``.

-  ``GENERATE_COT``: Boolean flag used to build and execute the ``cert_create``
   tool to create certificates as per the Chain of Trust described in
   `Trusted Board Boot`_. The build system then calls ``fiptool`` to
   include the certificates in the FIP and FWU_FIP. Default value is '0'.

   Specify both ``TRUSTED_BOARD_BOOT=1`` and ``GENERATE_COT=1`` to include support
   for the Trusted Board Boot feature in the BL1 and BL2 images, to generate
   the corresponding certificates, and to include those certificates in the
   FIP and FWU_FIP.

   Note that if ``TRUSTED_BOARD_BOOT=0`` and ``GENERATE_COT=1``, the BL1 and BL2
   images will not include support for Trusted Board Boot. The FIP will still
   include the corresponding certificates. This FIP can be used to verify the
   Chain of Trust on the host machine through other mechanisms.

   Note that if ``TRUSTED_BOARD_BOOT=1`` and ``GENERATE_COT=0``, the BL1 and BL2
   images will include support for Trusted Board Boot, but the FIP and FWU_FIP
   will not include the corresponding certificates, causing a boot failure.

-  ``GICV2_G0_FOR_EL3``: Unlike GICv3, the GICv2 architecture doesn't have
   inherent support for specific EL3 type interrupts. Setting this build option
   to ``1`` assumes GICv2 *Group 0* interrupts are expected to target EL3, both
   by `platform abstraction layer`__ and `Interrupt Management Framework`__.
   This allows GICv2 platforms to enable features requiring EL3 interrupt type.
   This also means that all GICv2 Group 0 interrupts are delivered to EL3, and
   the Secure Payload interrupts needs to be synchronously handed over to Secure
   EL1 for handling. The default value of this option is ``0``, which means the
   Group 0 interrupts are assumed to be handled by Secure EL1.

   .. __: `platform-interrupt-controller-API.rst`
   .. __: `interrupt-framework-design.rst`

-  ``HANDLE_EA_EL3_FIRST``: When set to ``1``, External Aborts and SError
   Interrupts will be always trapped in EL3 i.e. in BL31 at runtime. When set to
   ``0`` (default), these exceptions will be trapped in the current exception
   level (or in EL1 if the current exception level is EL0).

-  ``HW_ASSISTED_COHERENCY``: On most Arm systems to-date, platform-specific
   software operations are required for CPUs to enter and exit coherency.
   However, newer systems exist where CPUs' entry to and exit from coherency
   is managed in hardware. Such systems require software to only initiate these
   operations, and the rest is managed in hardware, minimizing active software
   management. In such systems, this boolean option enables TF-A to carry out
   build and run-time optimizations during boot and power management operations.
   This option defaults to 0 and if it is enabled, then it implies
   ``WARMBOOT_ENABLE_DCACHE_EARLY`` is also enabled.

   If this flag is disabled while the platform which TF-A is compiled for
   includes cores that manage coherency in hardware, then a compilation error is
   generated. This is based on the fact that a system cannot have, at the same
   time, cores that manage coherency in hardware and cores that don't. In other
   words, a platform cannot have, at the same time, cores that require
   ``HW_ASSISTED_COHERENCY=1`` and cores that require
   ``HW_ASSISTED_COHERENCY=0``.

   Note that, when ``HW_ASSISTED_COHERENCY`` is enabled, version 2 of
   translation library (xlat tables v2) must be used; version 1 of translation
   library is not supported.

-  ``JUNO_AARCH32_EL3_RUNTIME``: This build flag enables you to execute EL3
   runtime software in AArch32 mode, which is required to run AArch32 on Juno.
   By default this flag is set to '0'. Enabling this flag builds BL1 and BL2 in
   AArch64 and facilitates the loading of ``SP_MIN`` and BL33 as AArch32 executable
   images.

-  ``KEY_ALG``: This build flag enables the user to select the algorithm to be
   used for generating the PKCS keys and subsequent signing of the certificate.
   It accepts 2 values: ``rsa`` and ``ecdsa``. The default value of this flag
   is ``rsa`` which is the TBBR compliant PKCS#1 RSA 2.1 scheme.

-  ``KEY_SIZE``: This build flag enables the user to select the key size for
   the algorithm specified by ``KEY_ALG``. The valid values for ``KEY_SIZE``
   depend on the chosen algorithm.

   +-----------+------------------------------------+
   |  KEY_ALG  |        Possible key sizes          |
   +===========+====================================+
   |    rsa    |  1024, 2048 (default), 3072, 4096  |
   +-----------+------------------------------------+
   |   ecdsa   |            unavailable             |
   +-----------+------------------------------------+

-  ``HASH_ALG``: This build flag enables the user to select the secure hash
   algorithm. It accepts 3 values: ``sha256``, ``sha384`` and ``sha512``.
   The default value of this flag is ``sha256``.

-  ``LDFLAGS``: Extra user options appended to the linkers' command line in
   addition to the one set by the build system.

-  ``LOG_LEVEL``: Chooses the log level, which controls the amount of console log
   output compiled into the build. This should be one of the following:

   ::

       0  (LOG_LEVEL_NONE)
       10 (LOG_LEVEL_ERROR)
       20 (LOG_LEVEL_NOTICE)
       30 (LOG_LEVEL_WARNING)
       40 (LOG_LEVEL_INFO)
       50 (LOG_LEVEL_VERBOSE)

   All log output up to and including the selected log level is compiled into
   the build. The default value is 40 in debug builds and 20 in release builds.

-  ``NON_TRUSTED_WORLD_KEY``: This option is used when ``GENERATE_COT=1``. It
   specifies the file that contains the Non-Trusted World private key in PEM
   format. If ``SAVE_KEYS=1``, this file name will be used to save the key.

-  ``NS_BL2U``: Path to NS_BL2U image in the host file system. This image is
   optional. It is only needed if the platform makefile specifies that it
   is required in order to build the ``fwu_fip`` target.

-  ``NS_TIMER_SWITCH``: Enable save and restore for non-secure timer register
   contents upon world switch. It can take either 0 (don't save and restore) or
   1 (do save and restore). 0 is the default. An SPD may set this to 1 if it
   wants the timer registers to be saved and restored.

-  ``OVERRIDE_LIBC``: This option allows platforms to override the default libc
   for the BL image. It can be either 0 (include) or 1 (remove). The default
   value is 0.

-  ``PL011_GENERIC_UART``: Boolean option to indicate the PL011 driver that
   the underlying hardware is not a full PL011 UART but a minimally compliant
   generic UART, which is a subset of the PL011. The driver will not access
   any register that is not part of the SBSA generic UART specification.
   Default value is 0 (a full PL011 compliant UART is present).

-  ``PLAT``: Choose a platform to build TF-A for. The chosen platform name
   must be subdirectory of any depth under ``plat/``, and must contain a
   platform makefile named ``platform.mk``. For example, to build TF-A for the
   Arm Juno board, select PLAT=juno.

-  ``PRELOADED_BL33_BASE``: This option enables booting a preloaded BL33 image
   instead of the normal boot flow. When defined, it must specify the entry
   point address for the preloaded BL33 image. This option is incompatible with
   ``EL3_PAYLOAD_BASE``. If both are defined, ``EL3_PAYLOAD_BASE`` has priority
   over ``PRELOADED_BL33_BASE``.

-  ``PROGRAMMABLE_RESET_ADDRESS``: This option indicates whether the reset
   vector address can be programmed or is fixed on the platform. It can take
   either 0 (fixed) or 1 (programmable). Default is 0. If the platform has a
   programmable reset address, it is expected that a CPU will start executing
   code directly at the right address, both on a cold and warm reset. In this
   case, there is no need to identify the entrypoint on boot and the boot path
   can be optimised. The ``plat_get_my_entrypoint()`` platform porting interface
   does not need to be implemented in this case.

-  ``PSCI_EXTENDED_STATE_ID``: As per PSCI1.0 Specification, there are 2 formats
   possible for the PSCI power-state parameter: original and extended State-ID
   formats. This flag if set to 1, configures the generic PSCI layer to use the
   extended format. The default value of this flag is 0, which means by default
   the original power-state format is used by the PSCI implementation. This flag
   should be specified by the platform makefile and it governs the return value
   of PSCI_FEATURES API for CPU_SUSPEND smc function id. When this option is
   enabled on Arm platforms, the option ``ARM_RECOM_STATE_ID_ENC`` needs to be
   set to 1 as well.

-  ``RAS_EXTENSION``: When set to ``1``, enable Armv8.2 RAS features. RAS features
   are an optional extension for pre-Armv8.2 CPUs, but are mandatory for Armv8.2
   or later CPUs.

   When ``RAS_EXTENSION`` is set to ``1``, ``HANDLE_EA_EL3_FIRST`` must also be
   set to ``1``.

   This option is disabled by default.

-  ``RESET_TO_BL31``: Enable BL31 entrypoint as the CPU reset vector instead
   of the BL1 entrypoint. It can take the value 0 (CPU reset to BL1
   entrypoint) or 1 (CPU reset to BL31 entrypoint).
   The default value is 0.

-  ``RESET_TO_SP_MIN``: SP_MIN is the minimal AArch32 Secure Payload provided
   in TF-A. This flag configures SP_MIN entrypoint as the CPU reset vector
   instead of the BL1 entrypoint. It can take the value 0 (CPU reset to BL1
   entrypoint) or 1 (CPU reset to SP_MIN entrypoint). The default value is 0.

-  ``ROT_KEY``: This option is used when ``GENERATE_COT=1``. It specifies the
   file that contains the ROT private key in PEM format. If ``SAVE_KEYS=1``, this
   file name will be used to save the key.

-  ``SANITIZE_UB``: This option enables the Undefined Behaviour sanitizer. It
   can take 3 values: 'off' (default), 'on' and 'trap'. When using 'trap',
   gcc and clang will insert calls to ``__builtin_trap`` on detected
   undefined behaviour, which defaults to a ``brk`` instruction. When using
   'on', undefined behaviour is translated to a call to special handlers which
   prints the exact location of the problem and its cause and then panics.

    .. note::
        Because of the space penalty of the Undefined Behaviour sanitizer,
        this option will increase the size of the binary. Depending on the
        memory constraints of the target platform, it may not be possible to
        enable the sanitizer for all images (BL1 and BL2 are especially
        likely to be memory constrained). We recommend that the
        sanitizer is enabled only in debug builds.

-  ``SAVE_KEYS``: This option is used when ``GENERATE_COT=1``. It tells the
   certificate generation tool to save the keys used to establish the Chain of
   Trust. Allowed options are '0' or '1'. Default is '0' (do not save).

-  ``SCP_BL2``: Path to SCP_BL2 image in the host file system. This image is optional.
   If a SCP_BL2 image is present then this option must be passed for the ``fip``
   target.

-  ``SCP_BL2_KEY``: This option is used when ``GENERATE_COT=1``. It specifies the
   file that contains the SCP_BL2 private key in PEM format. If ``SAVE_KEYS=1``,
   this file name will be used to save the key.

-  ``SCP_BL2U``: Path to SCP_BL2U image in the host file system. This image is
   optional. It is only needed if the platform makefile specifies that it
   is required in order to build the ``fwu_fip`` target.

-  ``SDEI_SUPPORT``: Setting this to ``1`` enables support for Software
   Delegated Exception Interface to BL31 image. This defaults to ``0``.

   When set to ``1``, the build option ``EL3_EXCEPTION_HANDLING`` must also be
   set to ``1``.

-  ``SEPARATE_CODE_AND_RODATA``: Whether code and read-only data should be
   isolated on separate memory pages. This is a trade-off between security and
   memory usage. See "Isolating code and read-only data on separate memory
   pages" section in `Firmware Design`_. This flag is disabled by default and
   affects all BL images.

-  ``SPD``: Choose a Secure Payload Dispatcher component to be built into TF-A.
   This build option is only valid if ``ARCH=aarch64``. The value should be
   the path to the directory containing the SPD source, relative to
   ``services/spd/``; the directory is expected to contain a makefile called
   ``<spd-value>.mk``.

-  ``SPIN_ON_BL1_EXIT``: This option introduces an infinite loop in BL1. It can
   take either 0 (no loop) or 1 (add a loop). 0 is the default. This loop stops
   execution in BL1 just before handing over to BL31. At this point, all
   firmware images have been loaded in memory, and the MMU and caches are
   turned off. Refer to the "Debugging options" section for more details.

-  ``SP_MIN_WITH_SECURE_FIQ``: Boolean flag to indicate the SP_MIN handles
   secure interrupts (caught through the FIQ line). Platforms can enable
   this directive if they need to handle such interruption. When enabled,
   the FIQ are handled in monitor mode and non secure world is not allowed
   to mask these events. Platforms that enable FIQ handling in SP_MIN shall
   implement the api ``sp_min_plat_fiq_handler()``. The default value is 0.

-  ``TRUSTED_BOARD_BOOT``: Boolean flag to include support for the Trusted Board
   Boot feature. When set to '1', BL1 and BL2 images include support to load
   and verify the certificates and images in a FIP, and BL1 includes support
   for the Firmware Update. The default value is '0'. Generation and inclusion
   of certificates in the FIP and FWU_FIP depends upon the value of the
   ``GENERATE_COT`` option.

   .. warning::
      This option depends on ``CREATE_KEYS`` to be enabled. If the keys
      already exist in disk, they will be overwritten without further notice.

-  ``TRUSTED_WORLD_KEY``: This option is used when ``GENERATE_COT=1``. It
   specifies the file that contains the Trusted World private key in PEM
   format. If ``SAVE_KEYS=1``, this file name will be used to save the key.

-  ``TSP_INIT_ASYNC``: Choose BL32 initialization method as asynchronous or
   synchronous, (see "Initializing a BL32 Image" section in
   `Firmware Design`_). It can take the value 0 (BL32 is initialized using
   synchronous method) or 1 (BL32 is initialized using asynchronous method).
   Default is 0.

-  ``TSP_NS_INTR_ASYNC_PREEMPT``: A non zero value enables the interrupt
   routing model which routes non-secure interrupts asynchronously from TSP
   to EL3 causing immediate preemption of TSP. The EL3 is responsible
   for saving and restoring the TSP context in this routing model. The
   default routing model (when the value is 0) is to route non-secure
   interrupts to TSP allowing it to save its context and hand over
   synchronously to EL3 via an SMC.

   .. note::
      When ``EL3_EXCEPTION_HANDLING`` is ``1``, ``TSP_NS_INTR_ASYNC_PREEMPT``
      must also be set to ``1``.

-  ``USE_ARM_LINK``: This flag determines whether to enable support for ARM
   linker. When the ``LINKER`` build variable points to the armlink linker,
   this flag is enabled automatically. To enable support for armlink, platforms
   will have to provide a scatter file for the BL image. Currently, Tegra
   platforms use the armlink support to compile BL3-1 images.

-  ``USE_COHERENT_MEM``: This flag determines whether to include the coherent
   memory region in the BL memory map or not (see "Use of Coherent memory in
   TF-A" section in `Firmware Design`_). It can take the value 1
   (Coherent memory region is included) or 0 (Coherent memory region is
   excluded). Default is 1.

-  ``USE_ROMLIB``: This flag determines whether library at ROM will be used.
   This feature creates a library of functions to be placed in ROM and thus
   reduces SRAM usage. Refer to `Library at ROM`_ for further details. Default
   is 0.

-  ``USE_SPINLOCK_CAS``: Setting this build flag to 1 selects the spinlock
    implementation variant using the ARMv8.1-LSE compare-and-swap instruction.
    Notice this option is experimental and only available to AArch64 builds.

-  ``V``: Verbose build. If assigned anything other than 0, the build commands
   are printed. Default is 0.

-  ``VERSION_STRING``: String used in the log output for each TF-A image.
   Defaults to a string formed by concatenating the version number, build type
   and build string.

-  ``W``: Warning level. Some compiler warning options of interest have been
   regrouped and put in the root Makefile. This flag can take the values 0 to 3,
   each level enabling more warning options. Default is 0.

-  ``WARMBOOT_ENABLE_DCACHE_EARLY`` : Boolean option to enable D-cache early on
   the CPU after warm boot. This is applicable for platforms which do not
   require interconnect programming to enable cache coherency (eg: single
   cluster platforms). If this option is enabled, then warm boot path
   enables D-caches immediately after enabling MMU. This option defaults to 0.

Arm development platform specific build options
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

-  ``ARM_BL31_IN_DRAM``: Boolean option to select loading of BL31 in TZC secured
   DRAM. By default, BL31 is in the secure SRAM. Set this flag to 1 to load
   BL31 in TZC secured DRAM. If TSP is present, then setting this option also
   sets the TSP location to DRAM and ignores the ``ARM_TSP_RAM_LOCATION`` build
   flag.

-  ``ARM_CONFIG_CNTACR``: boolean option to unlock access to the ``CNTBase<N>``
   frame registers by setting the ``CNTCTLBase.CNTACR<N>`` register bits. The
   frame number ``<N>`` is defined by ``PLAT_ARM_NSTIMER_FRAME_ID``, which should
   match the frame used by the Non-Secure image (normally the Linux kernel).
   Default is true (access to the frame is allowed).

-  ``ARM_DISABLE_TRUSTED_WDOG``: boolean option to disable the Trusted Watchdog.
   By default, Arm platforms use a watchdog to trigger a system reset in case
   an error is encountered during the boot process (for example, when an image
   could not be loaded or authenticated). The watchdog is enabled in the early
   platform setup hook at BL1 and disabled in the BL1 prepare exit hook. The
   Trusted Watchdog may be disabled at build time for testing or development
   purposes.

-  ``ARM_LINUX_KERNEL_AS_BL33``: The Linux kernel expects registers x0-x3 to
   have specific values at boot. This boolean option allows the Trusted Firmware
   to have a Linux kernel image as BL33 by preparing the registers to these
   values before jumping to BL33. This option defaults to 0 (disabled). For
   AArch64 ``RESET_TO_BL31`` and for AArch32 ``RESET_TO_SP_MIN`` must be 1 when
   using it. If this option is set to 1, ``ARM_PRELOADED_DTB_BASE`` must be set
   to the location of a device tree blob (DTB) already loaded in memory. The
   Linux Image address must be specified using the ``PRELOADED_BL33_BASE``
   option.

-  ``ARM_PLAT_MT``: This flag determines whether the Arm platform layer has to
   cater for the multi-threading ``MT`` bit when accessing MPIDR. When this flag
   is set, the functions which deal with MPIDR assume that the ``MT`` bit in
   MPIDR is set and access the bit-fields in MPIDR accordingly. Default value of
   this flag is 0. Note that this option is not used on FVP platforms.

-  ``ARM_RECOM_STATE_ID_ENC``: The PSCI1.0 specification recommends an encoding
   for the construction of composite state-ID in the power-state parameter.
   The existing PSCI clients currently do not support this encoding of
   State-ID yet. Hence this flag is used to configure whether to use the
   recommended State-ID encoding or not. The default value of this flag is 0,
   in which case the platform is configured to expect NULL in the State-ID
   field of power-state parameter.

-  ``ARM_ROTPK_LOCATION``: used when ``TRUSTED_BOARD_BOOT=1``. It specifies the
   location of the ROTPK hash returned by the function ``plat_get_rotpk_info()``
   for Arm platforms. Depending on the selected option, the proper private key
   must be specified using the ``ROT_KEY`` option when building the Trusted
   Firmware. This private key will be used by the certificate generation tool
   to sign the BL2 and Trusted Key certificates. Available options for
   ``ARM_ROTPK_LOCATION`` are:

   -  ``regs`` : return the ROTPK hash stored in the Trusted root-key storage
      registers. The private key corresponding to this ROTPK hash is not
      currently available.
   -  ``devel_rsa`` : return a development public key hash embedded in the BL1
      and BL2 binaries. This hash has been obtained from the RSA public key
      ``arm_rotpk_rsa.der``, located in ``plat/arm/board/common/rotpk``. To use
      this option, ``arm_rotprivk_rsa.pem`` must be specified as ``ROT_KEY`` when
      creating the certificates.
   -  ``devel_ecdsa`` : return a development public key hash embedded in the BL1
      and BL2 binaries. This hash has been obtained from the ECDSA public key
      ``arm_rotpk_ecdsa.der``, located in ``plat/arm/board/common/rotpk``. To use
      this option, ``arm_rotprivk_ecdsa.pem`` must be specified as ``ROT_KEY``
      when creating the certificates.

-  ``ARM_TSP_RAM_LOCATION``: location of the TSP binary. Options:

   -  ``tsram`` : Trusted SRAM (default option when TBB is not enabled)
   -  ``tdram`` : Trusted DRAM (if available)
   -  ``dram`` : Secure region in DRAM (default option when TBB is enabled,
      configured by the TrustZone controller)

-  ``ARM_XLAT_TABLES_LIB_V1``: boolean option to compile TF-A with version 1
   of the translation tables library instead of version 2. It is set to 0 by
   default, which selects version 2.

-  ``ARM_CRYPTOCELL_INTEG`` : bool option to enable TF-A to invoke Arm®
   TrustZone® CryptoCell functionality for Trusted Board Boot on capable Arm
   platforms. If this option is specified, then the path to the CryptoCell
   SBROM library must be specified via ``CCSBROM_LIB_PATH`` flag.

For a better understanding of these options, the Arm development platform memory
map is explained in the `Firmware Design`_.

Arm CSS platform specific build options
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

-  ``CSS_DETECT_PRE_1_7_0_SCP``: Boolean flag to detect SCP version
   incompatibility. Version 1.7.0 of the SCP firmware made a non-backwards
   compatible change to the MTL protocol, used for AP/SCP communication.
   TF-A no longer supports earlier SCP versions. If this option is set to 1
   then TF-A will detect if an earlier version is in use. Default is 1.

-  ``CSS_LOAD_SCP_IMAGES``: Boolean flag, which when set, adds SCP_BL2 and
   SCP_BL2U to the FIP and FWU_FIP respectively, and enables them to be loaded
   during boot. Default is 1.

-  ``CSS_USE_SCMI_SDS_DRIVER``: Boolean flag which selects SCMI/SDS drivers
   instead of SCPI/BOM driver for communicating with the SCP during power
   management operations and for SCP RAM Firmware transfer. If this option
   is set to 1, then SCMI/SDS drivers will be used. Default is 0.

Arm FVP platform specific build options
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

-  ``FVP_CLUSTER_COUNT`` : Configures the cluster count to be used to
   build the topology tree within TF-A. By default TF-A is configured for dual
   cluster topology and this option can be used to override the default value.

-  ``FVP_INTERCONNECT_DRIVER``: Selects the interconnect driver to be built. The
   default interconnect driver depends on the value of ``FVP_CLUSTER_COUNT`` as
   explained in the options below:

   -  ``FVP_CCI`` : The CCI driver is selected. This is the default
      if 0 < ``FVP_CLUSTER_COUNT`` <= 2.
   -  ``FVP_CCN`` : The CCN driver is selected. This is the default
      if ``FVP_CLUSTER_COUNT`` > 2.

-  ``FVP_MAX_CPUS_PER_CLUSTER``: Sets the maximum number of CPUs implemented in
   a single cluster.  This option defaults to 4.

-  ``FVP_MAX_PE_PER_CPU``: Sets the maximum number of PEs implemented on any CPU
   in the system. This option defaults to 1. Note that the build option
   ``ARM_PLAT_MT`` doesn't have any effect on FVP platforms.

-  ``FVP_USE_GIC_DRIVER`` : Selects the GIC driver to be built. Options:

   -  ``FVP_GIC600`` : The GIC600 implementation of GICv3 is selected
   -  ``FVP_GICV2`` : The GICv2 only driver is selected
   -  ``FVP_GICV3`` : The GICv3 only driver is selected (default option)

-  ``FVP_USE_SP804_TIMER`` : Use the SP804 timer instead of the Generic Timer
   for functions that wait for an arbitrary time length (udelay and mdelay).
   The default value is 0.

-  ``FVP_HW_CONFIG_DTS`` : Specify the path to the DTS file to be compiled
   to DTB and packaged in FIP as the HW_CONFIG. See `Firmware Design`_ for
   details on HW_CONFIG. By default, this is initialized to a sensible DTS
   file in ``fdts/`` folder depending on other build options. But some cases,
   like shifted affinity format for MPIDR, cannot be detected at build time
   and this option is needed to specify the appropriate DTS file.

-  ``FVP_HW_CONFIG`` : Specify the path to the HW_CONFIG blob to be packaged in
   FIP. See `Firmware Design`_ for details on HW_CONFIG. This option is
   similar to the ``FVP_HW_CONFIG_DTS`` option, but it directly specifies the
   HW_CONFIG blob instead of the DTS file. This option is useful to override
   the default HW_CONFIG selected by the build system.

ARM JUNO platform specific build options
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

-  ``JUNO_TZMP1`` : Boolean option to configure Juno to be used for TrustZone
   Media Protection (TZ-MP1). Default value of this flag is 0.

Debugging options
~~~~~~~~~~~~~~~~~

To compile a debug version and make the build more verbose use

.. code:: shell

    make PLAT=<platform> DEBUG=1 V=1 all

AArch64 GCC uses DWARF version 4 debugging symbols by default. Some tools (for
example DS-5) might not support this and may need an older version of DWARF
symbols to be emitted by GCC. This can be achieved by using the
``-gdwarf-<version>`` flag, with the version being set to 2 or 3. Setting the
version to 2 is recommended for DS-5 versions older than 5.16.

When debugging logic problems it might also be useful to disable all compiler
optimizations by using ``-O0``.

.. warning::
   Using ``-O0`` could cause output images to be larger and base addresses
   might need to be recalculated (see the **Memory layout on Arm development
   platforms** section in the `Firmware Design`_).

Extra debug options can be passed to the build system by setting ``CFLAGS`` or
``LDFLAGS``:

.. code:: shell

    CFLAGS='-O0 -gdwarf-2'                                     \
    make PLAT=<platform> DEBUG=1 V=1 all

Note that using ``-Wl,`` style compilation driver options in ``CFLAGS`` will be
ignored as the linker is called directly.

It is also possible to introduce an infinite loop to help in debugging the
post-BL2 phase of TF-A. This can be done by rebuilding BL1 with the
``SPIN_ON_BL1_EXIT=1`` build flag. Refer to the `Summary of build options`_
section. In this case, the developer may take control of the target using a
debugger when indicated by the console output. When using DS-5, the following
commands can be used:

::

    # Stop target execution
    interrupt

    #
    # Prepare your debugging environment, e.g. set breakpoints
    #

    # Jump over the debug loop
    set var $AARCH64::$Core::$PC = $AARCH64::$Core::$PC + 4

    # Resume execution
    continue

Building the Test Secure Payload
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The TSP is coupled with a companion runtime service in the BL31 firmware,
called the TSPD. Therefore, if you intend to use the TSP, the BL31 image
must be recompiled as well. For more information on SPs and SPDs, see the
`Secure-EL1 Payloads and Dispatchers`_ section in the `Firmware Design`_.

First clean the TF-A build directory to get rid of any previous BL31 binary.
Then to build the TSP image use:

.. code:: shell

    make PLAT=<platform> SPD=tspd all

An additional boot loader binary file is created in the ``build`` directory:

::

    build/<platform>/<build-type>/bl32.bin


Building and using the FIP tool
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Firmware Image Package (FIP) is a packaging format used by TF-A to package
firmware images in a single binary. The number and type of images that should
be packed in a FIP is platform specific and may include TF-A images and other
firmware images required by the platform. For example, most platforms require
a BL33 image which corresponds to the normal world bootloader (e.g. UEFI or
U-Boot).

The TF-A build system provides the make target ``fip`` to create a FIP file
for the specified platform using the FIP creation tool included in the TF-A
project. Examples below show how to build a FIP file for FVP, packaging TF-A
and BL33 images.

For AArch64:

.. code:: shell

    make PLAT=fvp BL33=<path-to>/bl33.bin fip

For AArch32:

.. code:: shell

    make PLAT=fvp ARCH=aarch32 AARCH32_SP=sp_min BL33=<path-to>/bl33.bin fip

The resulting FIP may be found in:

::

    build/fvp/<build-type>/fip.bin

For advanced operations on FIP files, it is also possible to independently build
the tool and create or modify FIPs using this tool. To do this, follow these
steps:

It is recommended to remove old artifacts before building the tool:

.. code:: shell

    make -C tools/fiptool clean

Build the tool:

.. code:: shell

    make [DEBUG=1] [V=1] fiptool

The tool binary can be located in:

::

    ./tools/fiptool/fiptool

Invoking the tool with ``help`` will print a help message with all available
options.

Example 1: create a new Firmware package ``fip.bin`` that contains BL2 and BL31:

.. code:: shell

    ./tools/fiptool/fiptool create \
        --tb-fw build/<platform>/<build-type>/bl2.bin \
        --soc-fw build/<platform>/<build-type>/bl31.bin \
        fip.bin

Example 2: view the contents of an existing Firmware package:

.. code:: shell

    ./tools/fiptool/fiptool info <path-to>/fip.bin

Example 3: update the entries of an existing Firmware package:

.. code:: shell

    # Change the BL2 from Debug to Release version
    ./tools/fiptool/fiptool update \
        --tb-fw build/<platform>/release/bl2.bin \
        build/<platform>/debug/fip.bin

Example 4: unpack all entries from an existing Firmware package:

.. code:: shell

    # Images will be unpacked to the working directory
    ./tools/fiptool/fiptool unpack <path-to>/fip.bin

Example 5: remove an entry from an existing Firmware package:

.. code:: shell

    ./tools/fiptool/fiptool remove \
        --tb-fw build/<platform>/debug/fip.bin

Note that if the destination FIP file exists, the create, update and
remove operations will automatically overwrite it.

The unpack operation will fail if the images already exist at the
destination. In that case, use -f or --force to continue.

More information about FIP can be found in the `Firmware Design`_ document.

Building FIP images with support for Trusted Board Boot
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Trusted Board Boot primarily consists of the following two features:

-  Image Authentication, described in `Trusted Board Boot`_, and
-  Firmware Update, described in `Firmware Update`_

The following steps should be followed to build FIP and (optionally) FWU_FIP
images with support for these features:

#. Fulfill the dependencies of the ``mbedtls`` cryptographic and image parser
   modules by checking out a recent version of the `mbed TLS Repository`_. It
   is important to use a version that is compatible with TF-A and fixes any
   known security vulnerabilities. See `mbed TLS Security Center`_ for more
   information. The latest version of TF-A is tested with tag
   ``mbedtls-2.16.2``.

   The ``drivers/auth/mbedtls/mbedtls_*.mk`` files contain the list of mbed TLS
   source files the modules depend upon.
   ``include/drivers/auth/mbedtls/mbedtls_config.h`` contains the configuration
   options required to build the mbed TLS sources.

   Note that the mbed TLS library is licensed under the Apache version 2.0
   license. Using mbed TLS source code will affect the licensing of TF-A
   binaries that are built using this library.

#. To build the FIP image, ensure the following command line variables are set
   while invoking ``make`` to build TF-A:

   -  ``MBEDTLS_DIR=<path of the directory containing mbed TLS sources>``
   -  ``TRUSTED_BOARD_BOOT=1``
   -  ``GENERATE_COT=1``

   In the case of Arm platforms, the location of the ROTPK hash must also be
   specified at build time. Two locations are currently supported (see
   ``ARM_ROTPK_LOCATION`` build option):

   -  ``ARM_ROTPK_LOCATION=regs``: the ROTPK hash is obtained from the Trusted
      root-key storage registers present in the platform. On Juno, this
      registers are read-only. On FVP Base and Cortex models, the registers
      are read-only, but the value can be specified using the command line
      option ``bp.trusted_key_storage.public_key`` when launching the model.
      On both Juno and FVP models, the default value corresponds to an
      ECDSA-SECP256R1 public key hash, whose private part is not currently
      available.

   -  ``ARM_ROTPK_LOCATION=devel_rsa``: use the ROTPK hash that is hardcoded
      in the Arm platform port. The private/public RSA key pair may be
      found in ``plat/arm/board/common/rotpk``.

   -  ``ARM_ROTPK_LOCATION=devel_ecdsa``: use the ROTPK hash that is hardcoded
      in the Arm platform port. The private/public ECDSA key pair may be
      found in ``plat/arm/board/common/rotpk``.

   Example of command line using RSA development keys:

   .. code:: shell

       MBEDTLS_DIR=<path of the directory containing mbed TLS sources> \
       make PLAT=<platform> TRUSTED_BOARD_BOOT=1 GENERATE_COT=1        \
       ARM_ROTPK_LOCATION=devel_rsa                                    \
       ROT_KEY=plat/arm/board/common/rotpk/arm_rotprivk_rsa.pem        \
       BL33=<path-to>/<bl33_image>                                     \
       all fip

   The result of this build will be the bl1.bin and the fip.bin binaries. This
   FIP will include the certificates corresponding to the Chain of Trust
   described in the TBBR-client document. These certificates can also be found
   in the output build directory.

#. The optional FWU_FIP contains any additional images to be loaded from
   Non-Volatile storage during the `Firmware Update`_ process. To build the
   FWU_FIP, any FWU images required by the platform must be specified on the
   command line. On Arm development platforms like Juno, these are:

   -  NS_BL2U. The AP non-secure Firmware Updater image.
   -  SCP_BL2U. The SCP Firmware Update Configuration image.

   Example of Juno command line for generating both ``fwu`` and ``fwu_fip``
   targets using RSA development:

   ::

       MBEDTLS_DIR=<path of the directory containing mbed TLS sources> \
       make PLAT=juno TRUSTED_BOARD_BOOT=1 GENERATE_COT=1              \
       ARM_ROTPK_LOCATION=devel_rsa                                    \
       ROT_KEY=plat/arm/board/common/rotpk/arm_rotprivk_rsa.pem        \
       BL33=<path-to>/<bl33_image>                                     \
       SCP_BL2=<path-to>/<scp_bl2_image>                               \
       SCP_BL2U=<path-to>/<scp_bl2u_image>                             \
       NS_BL2U=<path-to>/<ns_bl2u_image>                               \
       all fip fwu_fip

   .. note::
      The BL2U image will be built by default and added to the FWU_FIP.
      The user may override this by adding ``BL2U=<path-to>/<bl2u_image>``
      to the command line above.

   .. note::
      Building and installing the non-secure and SCP FWU images (NS_BL1U,
      NS_BL2U and SCP_BL2U) is outside the scope of this document.

   The result of this build will be bl1.bin, fip.bin and fwu_fip.bin binaries.
   Both the FIP and FWU_FIP will include the certificates corresponding to the
   Chain of Trust described in the TBBR-client document. These certificates
   can also be found in the output build directory.

Building the Certificate Generation Tool
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The ``cert_create`` tool is built as part of the TF-A build process when the
``fip`` make target is specified and TBB is enabled (as described in the
previous section), but it can also be built separately with the following
command:

.. code:: shell

    make PLAT=<platform> [DEBUG=1] [V=1] certtool

For platforms that require their own IDs in certificate files, the generic
'cert_create' tool can be built with the following command. Note that the target
platform must define its IDs within a ``platform_oid.h`` header file for the
build to succeed.

.. code:: shell

    make PLAT=<platform> USE_TBBR_DEFS=0 [DEBUG=1] [V=1] certtool

``DEBUG=1`` builds the tool in debug mode. ``V=1`` makes the build process more
verbose. The following command should be used to obtain help about the tool:

.. code:: shell

    ./tools/cert_create/cert_create -h

Building a FIP for Juno and FVP
-------------------------------

This section provides Juno and FVP specific instructions to build Trusted
Firmware, obtain the additional required firmware, and pack it all together in
a single FIP binary. It assumes that a `Linaro Release`_ has been installed.

.. note::
   Pre-built binaries for AArch32 are available from Linaro Release 16.12
   onwards. Before that release, pre-built binaries are only available for
   AArch64.

.. warning::
   Follow the full instructions for one platform before switching to a
   different one. Mixing instructions for different platforms may result in
   corrupted binaries.

.. warning::
   The uboot image downloaded by the Linaro workspace script does not always
   match the uboot image packaged as BL33 in the corresponding fip file. It is
   recommended to use the version that is packaged in the fip file using the
   instructions below.

.. note::
   For the FVP, the kernel FDT is packaged in FIP during build and loaded
   by the firmware at runtime. See `Obtaining the Flattened Device Trees`_
   section for more info on selecting the right FDT to use.

#. Clean the working directory

   .. code:: shell

       make realclean

#. Obtain SCP_BL2 (Juno) and BL33 (all platforms)

   Use the fiptool to extract the SCP_BL2 and BL33 images from the FIP
   package included in the Linaro release:

   .. code:: shell

       # Build the fiptool
       make [DEBUG=1] [V=1] fiptool

       # Unpack firmware images from Linaro FIP
       ./tools/fiptool/fiptool unpack <path-to-linaro-release>/fip.bin

   The unpack operation will result in a set of binary images extracted to the
   current working directory. The SCP_BL2 image corresponds to
   ``scp-fw.bin`` and BL33 corresponds to ``nt-fw.bin``.

   .. note::
      The fiptool will complain if the images to be unpacked already
      exist in the current directory. If that is the case, either delete those
      files or use the ``--force`` option to overwrite.

   .. note::
      For AArch32, the instructions below assume that nt-fw.bin is a
      normal world boot loader that supports AArch32.

#. Build TF-A images and create a new FIP for FVP

   .. code:: shell

       # AArch64
       make PLAT=fvp BL33=nt-fw.bin all fip

       # AArch32
       make PLAT=fvp ARCH=aarch32 AARCH32_SP=sp_min BL33=nt-fw.bin all fip

#. Build TF-A images and create a new FIP for Juno

   For AArch64:

   Building for AArch64 on Juno simply requires the addition of ``SCP_BL2``
   as a build parameter.

   .. code:: shell

       make PLAT=juno BL33=nt-fw.bin SCP_BL2=scp-fw.bin all fip

   For AArch32:

   Hardware restrictions on Juno prevent cold reset into AArch32 execution mode,
   therefore BL1 and BL2 must be compiled for AArch64, and BL32 is compiled
   separately for AArch32.

   -  Before building BL32, the environment variable ``CROSS_COMPILE`` must point
      to the AArch32 cross compiler.

      .. code:: shell

          export CROSS_COMPILE=<path-to-aarch32-gcc>/bin/arm-linux-gnueabihf-

   -  Build BL32 in AArch32.

      .. code:: shell

          make ARCH=aarch32 PLAT=juno AARCH32_SP=sp_min \
          RESET_TO_SP_MIN=1 JUNO_AARCH32_EL3_RUNTIME=1 bl32

   -  Save ``bl32.bin`` to a temporary location and clean the build products.

      ::

          cp <path-to-build>/bl32.bin <path-to-temporary>
          make realclean

   -  Before building BL1 and BL2, the environment variable ``CROSS_COMPILE``
      must point to the AArch64 cross compiler.

      .. code:: shell

          export CROSS_COMPILE=<path-to-aarch64-gcc>/bin/aarch64-linux-gnu-

   -  The following parameters should be used to build BL1 and BL2 in AArch64
      and point to the BL32 file.

      .. code:: shell

          make ARCH=aarch64 PLAT=juno JUNO_AARCH32_EL3_RUNTIME=1 \
          BL33=nt-fw.bin SCP_BL2=scp-fw.bin \
          BL32=<path-to-temporary>/bl32.bin all fip

The resulting BL1 and FIP images may be found in:

::

    # Juno
    ./build/juno/release/bl1.bin
    ./build/juno/release/fip.bin

    # FVP
    ./build/fvp/release/bl1.bin
    ./build/fvp/release/fip.bin


Booting Firmware Update images
-------------------------------------

When Firmware Update (FWU) is enabled there are at least 2 new images
that have to be loaded, the Non-Secure FWU ROM (NS-BL1U), and the
FWU FIP.

Juno
~~~~

The new images must be programmed in flash memory by adding
an entry in the ``SITE1/HBI0262x/images.txt`` configuration file
on the Juno SD card (where ``x`` depends on the revision of the Juno board).
Refer to the `Juno Getting Started Guide`_, section 2.3 "Flash memory
programming" for more information. User should ensure these do not
overlap with any other entries in the file.

::

	NOR10UPDATE: AUTO                       ;Image Update:NONE/AUTO/FORCE
	NOR10ADDRESS: 0x00400000                ;Image Flash Address [ns_bl2u_base_address]
	NOR10FILE: \SOFTWARE\fwu_fip.bin        ;Image File Name
	NOR10LOAD: 00000000                     ;Image Load Address
	NOR10ENTRY: 00000000                    ;Image Entry Point

	NOR11UPDATE: AUTO                       ;Image Update:NONE/AUTO/FORCE
	NOR11ADDRESS: 0x03EB8000                ;Image Flash Address [ns_bl1u_base_address]
	NOR11FILE: \SOFTWARE\ns_bl1u.bin        ;Image File Name
	NOR11LOAD: 00000000                     ;Image Load Address

The address ns_bl1u_base_address is the value of NS_BL1U_BASE - 0x8000000.
In the same way, the address ns_bl2u_base_address is the value of
NS_BL2U_BASE - 0x8000000.

FVP
~~~

The additional fip images must be loaded with:

::

    --data cluster0.cpu0="<path_to>/ns_bl1u.bin"@0x0beb8000	[ns_bl1u_base_address]
    --data cluster0.cpu0="<path_to>/fwu_fip.bin"@0x08400000	[ns_bl2u_base_address]

The address ns_bl1u_base_address is the value of NS_BL1U_BASE.
In the same way, the address ns_bl2u_base_address is the value of
NS_BL2U_BASE.


EL3 payloads alternative boot flow
----------------------------------

On a pre-production system, the ability to execute arbitrary, bare-metal code at
the highest exception level is required. It allows full, direct access to the
hardware, for example to run silicon soak tests.

Although it is possible to implement some baremetal secure firmware from
scratch, this is a complex task on some platforms, depending on the level of
configuration required to put the system in the expected state.

Rather than booting a baremetal application, a possible compromise is to boot
``EL3 payloads`` through TF-A instead. This is implemented as an alternative
boot flow, where a modified BL2 boots an EL3 payload, instead of loading the
other BL images and passing control to BL31. It reduces the complexity of
developing EL3 baremetal code by:

-  putting the system into a known architectural state;
-  taking care of platform secure world initialization;
-  loading the SCP_BL2 image if required by the platform.

When booting an EL3 payload on Arm standard platforms, the configuration of the
TrustZone controller is simplified such that only region 0 is enabled and is
configured to permit secure access only. This gives full access to the whole
DRAM to the EL3 payload.

The system is left in the same state as when entering BL31 in the default boot
flow. In particular:

-  Running in EL3;
-  Current state is AArch64;
-  Little-endian data access;
-  All exceptions disabled;
-  MMU disabled;
-  Caches disabled.

Booting an EL3 payload
~~~~~~~~~~~~~~~~~~~~~~

The EL3 payload image is a standalone image and is not part of the FIP. It is
not loaded by TF-A. Therefore, there are 2 possible scenarios:

-  The EL3 payload may reside in non-volatile memory (NVM) and execute in
   place. In this case, booting it is just a matter of specifying the right
   address in NVM through ``EL3_PAYLOAD_BASE`` when building TF-A.

-  The EL3 payload needs to be loaded in volatile memory (e.g. DRAM) at
   run-time.

To help in the latter scenario, the ``SPIN_ON_BL1_EXIT=1`` build option can be
used. The infinite loop that it introduces in BL1 stops execution at the right
moment for a debugger to take control of the target and load the payload (for
example, over JTAG).

It is expected that this loading method will work in most cases, as a debugger
connection is usually available in a pre-production system. The user is free to
use any other platform-specific mechanism to load the EL3 payload, though.

Booting an EL3 payload on FVP
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The EL3 payloads boot flow requires the CPU's mailbox to be cleared at reset for
the secondary CPUs holding pen to work properly. Unfortunately, its reset value
is undefined on the FVP platform and the FVP platform code doesn't clear it.
Therefore, one must modify the way the model is normally invoked in order to
clear the mailbox at start-up.

One way to do that is to create an 8-byte file containing all zero bytes using
the following command:

.. code:: shell

    dd if=/dev/zero of=mailbox.dat bs=1 count=8

and pre-load it into the FVP memory at the mailbox address (i.e. ``0x04000000``)
using the following model parameters:

::

    --data cluster0.cpu0=mailbox.dat@0x04000000   [Base FVPs]
    --data=mailbox.dat@0x04000000                 [Foundation FVP]

To provide the model with the EL3 payload image, the following methods may be
used:

#. If the EL3 payload is able to execute in place, it may be programmed into
   flash memory. On Base Cortex and AEM FVPs, the following model parameter
   loads it at the base address of the NOR FLASH1 (the NOR FLASH0 is already
   used for the FIP):

   ::

       -C bp.flashloader1.fname="<path-to>/<el3-payload>"

   On Foundation FVP, there is no flash loader component and the EL3 payload
   may be programmed anywhere in flash using method 3 below.

#. When using the ``SPIN_ON_BL1_EXIT=1`` loading method, the following DS-5
   command may be used to load the EL3 payload ELF image over JTAG:

   ::

       load <path-to>/el3-payload.elf

#. The EL3 payload may be pre-loaded in volatile memory using the following
   model parameters:

   ::

       --data cluster0.cpu0="<path-to>/el3-payload>"@address   [Base FVPs]
       --data="<path-to>/<el3-payload>"@address                [Foundation FVP]

   The address provided to the FVP must match the ``EL3_PAYLOAD_BASE`` address
   used when building TF-A.

Booting an EL3 payload on Juno
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If the EL3 payload is able to execute in place, it may be programmed in flash
memory by adding an entry in the ``SITE1/HBI0262x/images.txt`` configuration file
on the Juno SD card (where ``x`` depends on the revision of the Juno board).
Refer to the `Juno Getting Started Guide`_, section 2.3 "Flash memory
programming" for more information.

Alternatively, the same DS-5 command mentioned in the FVP section above can
be used to load the EL3 payload's ELF file over JTAG on Juno.

Preloaded BL33 alternative boot flow
------------------------------------

Some platforms have the ability to preload BL33 into memory instead of relying
on TF-A to load it. This may simplify packaging of the normal world code and
improve performance in a development environment. When secure world cold boot
is complete, TF-A simply jumps to a BL33 base address provided at build time.

For this option to be used, the ``PRELOADED_BL33_BASE`` build option has to be
used when compiling TF-A. For example, the following command will create a FIP
without a BL33 and prepare to jump to a BL33 image loaded at address
0x80000000:

.. code:: shell

    make PRELOADED_BL33_BASE=0x80000000 PLAT=fvp all fip

Boot of a preloaded kernel image on Base FVP
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The following example uses a simplified boot flow by directly jumping from the
TF-A to the Linux kernel, which will use a ramdisk as filesystem. This can be
useful if both the kernel and the device tree blob (DTB) are already present in
memory (like in FVP).

For example, if the kernel is loaded at ``0x80080000`` and the DTB is loaded at
address ``0x82000000``, the firmware can be built like this:

.. code:: shell

    CROSS_COMPILE=aarch64-linux-gnu-  \
    make PLAT=fvp DEBUG=1             \
    RESET_TO_BL31=1                   \
    ARM_LINUX_KERNEL_AS_BL33=1        \
    PRELOADED_BL33_BASE=0x80080000    \
    ARM_PRELOADED_DTB_BASE=0x82000000 \
    all fip

Now, it is needed to modify the DTB so that the kernel knows the address of the
ramdisk. The following script generates a patched DTB from the provided one,
assuming that the ramdisk is loaded at address ``0x84000000``. Note that this
script assumes that the user is using a ramdisk image prepared for U-Boot, like
the ones provided by Linaro. If using a ramdisk without this header,the ``0x40``
offset in ``INITRD_START`` has to be removed.

.. code:: bash

    #!/bin/bash

    # Path to the input DTB
    KERNEL_DTB=<path-to>/<fdt>
    # Path to the output DTB
    PATCHED_KERNEL_DTB=<path-to>/<patched-fdt>
    # Base address of the ramdisk
    INITRD_BASE=0x84000000
    # Path to the ramdisk
    INITRD=<path-to>/<ramdisk.img>

    # Skip uboot header (64 bytes)
    INITRD_START=$(printf "0x%x" $((${INITRD_BASE} + 0x40)) )
    INITRD_SIZE=$(stat -Lc %s ${INITRD})
    INITRD_END=$(printf "0x%x" $((${INITRD_BASE} + ${INITRD_SIZE})) )

    CHOSEN_NODE=$(echo                                        \
    "/ {                                                      \
            chosen {                                          \
                    linux,initrd-start = <${INITRD_START}>;   \
                    linux,initrd-end = <${INITRD_END}>;       \
            };                                                \
    };")

    echo $(dtc -O dts -I dtb ${KERNEL_DTB}) ${CHOSEN_NODE} |  \
            dtc -O dtb -o ${PATCHED_KERNEL_DTB} -

And the FVP binary can be run with the following command:

.. code:: shell

    <path-to>/FVP_Base_AEMv8A-AEMv8A                            \
    -C pctl.startup=0.0.0.0                                     \
    -C bp.secure_memory=1                                       \
    -C cluster0.NUM_CORES=4                                     \
    -C cluster1.NUM_CORES=4                                     \
    -C cache_state_modelled=1                                   \
    -C cluster0.cpu0.RVBAR=0x04020000                           \
    -C cluster0.cpu1.RVBAR=0x04020000                           \
    -C cluster0.cpu2.RVBAR=0x04020000                           \
    -C cluster0.cpu3.RVBAR=0x04020000                           \
    -C cluster1.cpu0.RVBAR=0x04020000                           \
    -C cluster1.cpu1.RVBAR=0x04020000                           \
    -C cluster1.cpu2.RVBAR=0x04020000                           \
    -C cluster1.cpu3.RVBAR=0x04020000                           \
    --data cluster0.cpu0="<path-to>/bl31.bin"@0x04020000        \
    --data cluster0.cpu0="<path-to>/<patched-fdt>"@0x82000000   \
    --data cluster0.cpu0="<path-to>/<kernel-binary>"@0x80080000 \
    --data cluster0.cpu0="<path-to>/<ramdisk.img>"@0x84000000

Boot of a preloaded kernel image on Juno
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Trusted Firmware must be compiled in a similar way as for FVP explained
above. The process to load binaries to memory is the one explained in
`Booting an EL3 payload on Juno`_.

Running the software on FVP
---------------------------

The latest version of the AArch64 build of TF-A has been tested on the following
Arm FVPs without shifted affinities, and that do not support threaded CPU cores
(64-bit host machine only).

.. note::
   The FVP models used are Version 11.6 Build 45, unless otherwise stated.

-  ``FVP_Base_AEMv8A-AEMv8A``
-  ``FVP_Base_AEMv8A-AEMv8A-AEMv8A-AEMv8A-CCN502``
-  ``FVP_Base_RevC-2xAEMv8A``
-  ``FVP_Base_Cortex-A32x4``
-  ``FVP_Base_Cortex-A35x4``
-  ``FVP_Base_Cortex-A53x4``
-  ``FVP_Base_Cortex-A55x4+Cortex-A75x4``
-  ``FVP_Base_Cortex-A55x4``
-  ``FVP_Base_Cortex-A57x1-A53x1``
-  ``FVP_Base_Cortex-A57x2-A53x4``
-  ``FVP_Base_Cortex-A57x4-A53x4``
-  ``FVP_Base_Cortex-A57x4``
-  ``FVP_Base_Cortex-A72x4-A53x4``
-  ``FVP_Base_Cortex-A72x4``
-  ``FVP_Base_Cortex-A73x4-A53x4``
-  ``FVP_Base_Cortex-A73x4``
-  ``FVP_Base_Cortex-A75x4``
-  ``FVP_Base_Cortex-A76x4``
-  ``FVP_Base_Cortex-A76AEx4``
-  ``FVP_Base_Cortex-A76AEx8``
-  ``FVP_Base_Cortex-A77x4`` (Version 11.7 build 36)
-  ``FVP_Base_Neoverse-N1x4``
-  ``FVP_CSS_SGI-575`` (Version 11.3 build 42)
-  ``FVP_CSS_SGM-775`` (Version 11.3 build 42)
-  ``FVP_RD_E1Edge`` (Version 11.3 build 42)
-  ``FVP_RD_N1Edge``
-  ``Foundation_Platform``

The latest version of the AArch32 build of TF-A has been tested on the following
Arm FVPs without shifted affinities, and that do not support threaded CPU cores
(64-bit host machine only).

-  ``FVP_Base_AEMv8A-AEMv8A``
-  ``FVP_Base_Cortex-A32x4``

.. note::
   The ``FVP_Base_RevC-2xAEMv8A`` FVP only supports shifted affinities, which
   is not compatible with legacy GIC configurations. Therefore this FVP does not
   support these legacy GIC configurations.

.. note::
   The build numbers quoted above are those reported by launching the FVP
   with the ``--version`` parameter.

.. note::
   Linaro provides a ramdisk image in prebuilt FVP configurations and full
   file systems that can be downloaded separately. To run an FVP with a virtio
   file system image an additional FVP configuration option
   ``-C bp.virtioblockdevice.image_path="<path-to>/<file-system-image>`` can be
   used.

.. note::
   The software will not work on Version 1.0 of the Foundation FVP.
   The commands below would report an ``unhandled argument`` error in this case.

.. note::
   FVPs can be launched with ``--cadi-server`` option such that a
   CADI-compliant debugger (for example, Arm DS-5) can connect to and control
   its execution.

.. warning::
   Since FVP model Version 11.0 Build 11.0.34 and Version 8.5 Build 0.8.5202
   the internal synchronisation timings changed compared to older versions of
   the models. The models can be launched with ``-Q 100`` option if they are
   required to match the run time characteristics of the older versions.

The Foundation FVP is a cut down version of the AArch64 Base FVP. It can be
downloaded for free from `Arm's website`_.

The Cortex-A models listed above are also available to download from
`Arm's website`_.

Please refer to the FVP documentation for a detailed description of the model
parameter options. A brief description of the important ones that affect TF-A
and normal world software behavior is provided below.

Obtaining the Flattened Device Trees
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Depending on the FVP configuration and Linux configuration used, different
FDT files are required. FDT source files for the Foundation and Base FVPs can
be found in the TF-A source directory under ``fdts/``. The Foundation FVP has
a subset of the Base FVP components. For example, the Foundation FVP lacks
CLCD and MMC support, and has only one CPU cluster.

.. note::
   It is not recommended to use the FDTs built along the kernel because not
   all FDTs are available from there.

The dynamic configuration capability is enabled in the firmware for FVPs.
This means that the firmware can authenticate and load the FDT if present in
FIP. A default FDT is packaged into FIP during the build based on
the build configuration. This can be overridden by using the ``FVP_HW_CONFIG``
or ``FVP_HW_CONFIG_DTS`` build options (refer to the
`Arm FVP platform specific build options`_ section for detail on the options).

-  ``fvp-base-gicv2-psci.dts``

   For use with models such as the Cortex-A57-A53 Base FVPs without shifted
   affinities and with Base memory map configuration.

-  ``fvp-base-gicv2-psci-aarch32.dts``

   For use with models such as the Cortex-A32 Base FVPs without shifted
   affinities and running Linux in AArch32 state with Base memory map
   configuration.

-  ``fvp-base-gicv3-psci.dts``

   For use with models such as the Cortex-A57-A53 Base FVPs without shifted
   affinities and with Base memory map configuration and Linux GICv3 support.

-  ``fvp-base-gicv3-psci-1t.dts``

   For use with models such as the AEMv8-RevC Base FVP with shifted affinities,
   single threaded CPUs, Base memory map configuration and Linux GICv3 support.

-  ``fvp-base-gicv3-psci-dynamiq.dts``

   For use with models as the Cortex-A55-A75 Base FVPs with shifted affinities,
   single cluster, single threaded CPUs, Base memory map configuration and Linux
   GICv3 support.

-  ``fvp-base-gicv3-psci-aarch32.dts``

   For use with models such as the Cortex-A32 Base FVPs without shifted
   affinities and running Linux in AArch32 state with Base memory map
   configuration and Linux GICv3 support.

-  ``fvp-foundation-gicv2-psci.dts``

   For use with Foundation FVP with Base memory map configuration.

-  ``fvp-foundation-gicv3-psci.dts``

   (Default) For use with Foundation FVP with Base memory map configuration
   and Linux GICv3 support.

Running on the Foundation FVP with reset to BL1 entrypoint
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The following ``Foundation_Platform`` parameters should be used to boot Linux with
4 CPUs using the AArch64 build of TF-A.

.. code:: shell

    <path-to>/Foundation_Platform                   \
    --cores=4                                       \
    --arm-v8.0                                      \
    --secure-memory                                 \
    --visualization                                 \
    --gicv3                                         \
    --data="<path-to>/<bl1-binary>"@0x0             \
    --data="<path-to>/<FIP-binary>"@0x08000000      \
    --data="<path-to>/<kernel-binary>"@0x80080000   \
    --data="<path-to>/<ramdisk-binary>"@0x84000000

Notes:

-  BL1 is loaded at the start of the Trusted ROM.
-  The Firmware Image Package is loaded at the start of NOR FLASH0.
-  The firmware loads the FDT packaged in FIP to the DRAM. The FDT load address
   is specified via the ``hw_config_addr`` property in `TB_FW_CONFIG for FVP`_.
-  The default use-case for the Foundation FVP is to use the ``--gicv3`` option
   and enable the GICv3 device in the model. Note that without this option,
   the Foundation FVP defaults to legacy (Versatile Express) memory map which
   is not supported by TF-A.
-  In order for TF-A to run correctly on the Foundation FVP, the architecture
   versions must match. The Foundation FVP defaults to the highest v8.x
   version it supports but the default build for TF-A is for v8.0. To avoid
   issues either start the Foundation FVP to use v8.0 architecture using the
   ``--arm-v8.0`` option, or build TF-A with an appropriate value for
   ``ARM_ARCH_MINOR``.

Running on the AEMv8 Base FVP with reset to BL1 entrypoint
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The following ``FVP_Base_RevC-2xAEMv8A`` parameters should be used to boot Linux
with 8 CPUs using the AArch64 build of TF-A.

.. code:: shell

    <path-to>/FVP_Base_RevC-2xAEMv8A                            \
    -C pctl.startup=0.0.0.0                                     \
    -C bp.secure_memory=1                                       \
    -C bp.tzc_400.diagnostics=1                                 \
    -C cluster0.NUM_CORES=4                                     \
    -C cluster1.NUM_CORES=4                                     \
    -C cache_state_modelled=1                                   \
    -C bp.secureflashloader.fname="<path-to>/<bl1-binary>"      \
    -C bp.flashloader0.fname="<path-to>/<FIP-binary>"           \
    --data cluster0.cpu0="<path-to>/<kernel-binary>"@0x80080000 \
    --data cluster0.cpu0="<path-to>/<ramdisk>"@0x84000000

.. note::
   The ``FVP_Base_RevC-2xAEMv8A`` has shifted affinities and requires
   a specific DTS for all the CPUs to be loaded.

Running on the AEMv8 Base FVP (AArch32) with reset to BL1 entrypoint
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The following ``FVP_Base_AEMv8A-AEMv8A`` parameters should be used to boot Linux
with 8 CPUs using the AArch32 build of TF-A.

.. code:: shell

    <path-to>/FVP_Base_AEMv8A-AEMv8A                            \
    -C pctl.startup=0.0.0.0                                     \
    -C bp.secure_memory=1                                       \
    -C bp.tzc_400.diagnostics=1                                 \
    -C cluster0.NUM_CORES=4                                     \
    -C cluster1.NUM_CORES=4                                     \
    -C cache_state_modelled=1                                   \
    -C cluster0.cpu0.CONFIG64=0                                 \
    -C cluster0.cpu1.CONFIG64=0                                 \
    -C cluster0.cpu2.CONFIG64=0                                 \
    -C cluster0.cpu3.CONFIG64=0                                 \
    -C cluster1.cpu0.CONFIG64=0                                 \
    -C cluster1.cpu1.CONFIG64=0                                 \
    -C cluster1.cpu2.CONFIG64=0                                 \
    -C cluster1.cpu3.CONFIG64=0                                 \
    -C bp.secureflashloader.fname="<path-to>/<bl1-binary>"      \
    -C bp.flashloader0.fname="<path-to>/<FIP-binary>"           \
    --data cluster0.cpu0="<path-to>/<kernel-binary>"@0x80080000 \
    --data cluster0.cpu0="<path-to>/<ramdisk>"@0x84000000

Running on the Cortex-A57-A53 Base FVP with reset to BL1 entrypoint
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The following ``FVP_Base_Cortex-A57x4-A53x4`` model parameters should be used to
boot Linux with 8 CPUs using the AArch64 build of TF-A.

.. code:: shell

    <path-to>/FVP_Base_Cortex-A57x4-A53x4                       \
    -C pctl.startup=0.0.0.0                                     \
    -C bp.secure_memory=1                                       \
    -C bp.tzc_400.diagnostics=1                                 \
    -C cache_state_modelled=1                                   \
    -C bp.secureflashloader.fname="<path-to>/<bl1-binary>"      \
    -C bp.flashloader0.fname="<path-to>/<FIP-binary>"           \
    --data cluster0.cpu0="<path-to>/<kernel-binary>"@0x80080000 \
    --data cluster0.cpu0="<path-to>/<ramdisk>"@0x84000000

Running on the Cortex-A32 Base FVP (AArch32) with reset to BL1 entrypoint
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The following ``FVP_Base_Cortex-A32x4`` model parameters should be used to
boot Linux with 4 CPUs using the AArch32 build of TF-A.

.. code:: shell

    <path-to>/FVP_Base_Cortex-A32x4                             \
    -C pctl.startup=0.0.0.0                                     \
    -C bp.secure_memory=1                                       \
    -C bp.tzc_400.diagnostics=1                                 \
    -C cache_state_modelled=1                                   \
    -C bp.secureflashloader.fname="<path-to>/<bl1-binary>"      \
    -C bp.flashloader0.fname="<path-to>/<FIP-binary>"           \
    --data cluster0.cpu0="<path-to>/<kernel-binary>"@0x80080000 \
    --data cluster0.cpu0="<path-to>/<ramdisk>"@0x84000000

Running on the AEMv8 Base FVP with reset to BL31 entrypoint
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The following ``FVP_Base_RevC-2xAEMv8A`` parameters should be used to boot Linux
with 8 CPUs using the AArch64 build of TF-A.

.. code:: shell

    <path-to>/FVP_Base_RevC-2xAEMv8A                             \
    -C pctl.startup=0.0.0.0                                      \
    -C bp.secure_memory=1                                        \
    -C bp.tzc_400.diagnostics=1                                  \
    -C cluster0.NUM_CORES=4                                      \
    -C cluster1.NUM_CORES=4                                      \
    -C cache_state_modelled=1                                    \
    -C cluster0.cpu0.RVBAR=0x04010000                            \
    -C cluster0.cpu1.RVBAR=0x04010000                            \
    -C cluster0.cpu2.RVBAR=0x04010000                            \
    -C cluster0.cpu3.RVBAR=0x04010000                            \
    -C cluster1.cpu0.RVBAR=0x04010000                            \
    -C cluster1.cpu1.RVBAR=0x04010000                            \
    -C cluster1.cpu2.RVBAR=0x04010000                            \
    -C cluster1.cpu3.RVBAR=0x04010000                            \
    --data cluster0.cpu0="<path-to>/<bl31-binary>"@0x04010000    \
    --data cluster0.cpu0="<path-to>/<bl32-binary>"@0xff000000    \
    --data cluster0.cpu0="<path-to>/<bl33-binary>"@0x88000000    \
    --data cluster0.cpu0="<path-to>/<fdt>"@0x82000000            \
    --data cluster0.cpu0="<path-to>/<kernel-binary>"@0x80080000  \
    --data cluster0.cpu0="<path-to>/<ramdisk>"@0x84000000

Notes:

-  If Position Independent Executable (PIE) support is enabled for BL31
   in this config, it can be loaded at any valid address for execution.

-  Since a FIP is not loaded when using BL31 as reset entrypoint, the
   ``--data="<path-to><bl31|bl32|bl33-binary>"@<base-address-of-binary>``
   parameter is needed to load the individual bootloader images in memory.
   BL32 image is only needed if BL31 has been built to expect a Secure-EL1
   Payload. For the same reason, the FDT needs to be compiled from the DT source
   and loaded via the ``--data cluster0.cpu0="<path-to>/<fdt>"@0x82000000``
   parameter.

-  The ``FVP_Base_RevC-2xAEMv8A`` has shifted affinities and requires a
   specific DTS for all the CPUs to be loaded.

-  The ``-C cluster<X>.cpu<Y>.RVBAR=@<base-address-of-bl31>`` parameter, where
   X and Y are the cluster and CPU numbers respectively, is used to set the
   reset vector for each core.

-  Changing the default value of ``ARM_TSP_RAM_LOCATION`` will also require
   changing the value of
   ``--data="<path-to><bl32-binary>"@<base-address-of-bl32>`` to the new value of
   ``BL32_BASE``.

Running on the AEMv8 Base FVP (AArch32) with reset to SP_MIN entrypoint
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The following ``FVP_Base_AEMv8A-AEMv8A`` parameters should be used to boot Linux
with 8 CPUs using the AArch32 build of TF-A.

.. code:: shell

    <path-to>/FVP_Base_AEMv8A-AEMv8A                             \
    -C pctl.startup=0.0.0.0                                      \
    -C bp.secure_memory=1                                        \
    -C bp.tzc_400.diagnostics=1                                  \
    -C cluster0.NUM_CORES=4                                      \
    -C cluster1.NUM_CORES=4                                      \
    -C cache_state_modelled=1                                    \
    -C cluster0.cpu0.CONFIG64=0                                  \
    -C cluster0.cpu1.CONFIG64=0                                  \
    -C cluster0.cpu2.CONFIG64=0                                  \
    -C cluster0.cpu3.CONFIG64=0                                  \
    -C cluster1.cpu0.CONFIG64=0                                  \
    -C cluster1.cpu1.CONFIG64=0                                  \
    -C cluster1.cpu2.CONFIG64=0                                  \
    -C cluster1.cpu3.CONFIG64=0                                  \
    -C cluster0.cpu0.RVBAR=0x04002000                            \
    -C cluster0.cpu1.RVBAR=0x04002000                            \
    -C cluster0.cpu2.RVBAR=0x04002000                            \
    -C cluster0.cpu3.RVBAR=0x04002000                            \
    -C cluster1.cpu0.RVBAR=0x04002000                            \
    -C cluster1.cpu1.RVBAR=0x04002000                            \
    -C cluster1.cpu2.RVBAR=0x04002000                            \
    -C cluster1.cpu3.RVBAR=0x04002000                            \
    --data cluster0.cpu0="<path-to>/<bl32-binary>"@0x04002000    \
    --data cluster0.cpu0="<path-to>/<bl33-binary>"@0x88000000    \
    --data cluster0.cpu0="<path-to>/<fdt>"@0x82000000            \
    --data cluster0.cpu0="<path-to>/<kernel-binary>"@0x80080000  \
    --data cluster0.cpu0="<path-to>/<ramdisk>"@0x84000000

.. note::
   The load address of ``<bl32-binary>`` depends on the value ``BL32_BASE``.
   It should match the address programmed into the RVBAR register as well.

Running on the Cortex-A57-A53 Base FVP with reset to BL31 entrypoint
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The following ``FVP_Base_Cortex-A57x4-A53x4`` model parameters should be used to
boot Linux with 8 CPUs using the AArch64 build of TF-A.

.. code:: shell

    <path-to>/FVP_Base_Cortex-A57x4-A53x4                        \
    -C pctl.startup=0.0.0.0                                      \
    -C bp.secure_memory=1                                        \
    -C bp.tzc_400.diagnostics=1                                  \
    -C cache_state_modelled=1                                    \
    -C cluster0.cpu0.RVBARADDR=0x04010000                        \
    -C cluster0.cpu1.RVBARADDR=0x04010000                        \
    -C cluster0.cpu2.RVBARADDR=0x04010000                        \
    -C cluster0.cpu3.RVBARADDR=0x04010000                        \
    -C cluster1.cpu0.RVBARADDR=0x04010000                        \
    -C cluster1.cpu1.RVBARADDR=0x04010000                        \
    -C cluster1.cpu2.RVBARADDR=0x04010000                        \
    -C cluster1.cpu3.RVBARADDR=0x04010000                        \
    --data cluster0.cpu0="<path-to>/<bl31-binary>"@0x04010000    \
    --data cluster0.cpu0="<path-to>/<bl32-binary>"@0xff000000    \
    --data cluster0.cpu0="<path-to>/<bl33-binary>"@0x88000000    \
    --data cluster0.cpu0="<path-to>/<fdt>"@0x82000000            \
    --data cluster0.cpu0="<path-to>/<kernel-binary>"@0x80080000  \
    --data cluster0.cpu0="<path-to>/<ramdisk>"@0x84000000

Running on the Cortex-A32 Base FVP (AArch32) with reset to SP_MIN entrypoint
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The following ``FVP_Base_Cortex-A32x4`` model parameters should be used to
boot Linux with 4 CPUs using the AArch32 build of TF-A.

.. code:: shell

    <path-to>/FVP_Base_Cortex-A32x4                             \
    -C pctl.startup=0.0.0.0                                     \
    -C bp.secure_memory=1                                       \
    -C bp.tzc_400.diagnostics=1                                 \
    -C cache_state_modelled=1                                   \
    -C cluster0.cpu0.RVBARADDR=0x04002000                       \
    -C cluster0.cpu1.RVBARADDR=0x04002000                       \
    -C cluster0.cpu2.RVBARADDR=0x04002000                       \
    -C cluster0.cpu3.RVBARADDR=0x04002000                       \
    --data cluster0.cpu0="<path-to>/<bl32-binary>"@0x04002000   \
    --data cluster0.cpu0="<path-to>/<bl33-binary>"@0x88000000   \
    --data cluster0.cpu0="<path-to>/<fdt>"@0x82000000           \
    --data cluster0.cpu0="<path-to>/<kernel-binary>"@0x80080000 \
    --data cluster0.cpu0="<path-to>/<ramdisk>"@0x84000000

Running the software on Juno
----------------------------

This version of TF-A has been tested on variants r0, r1 and r2 of Juno.

To execute the software stack on Juno, installing the latest Arm Platforms
software deliverables is recommended. Please install the deliverables by
following the `Instructions for using Linaro's deliverables on Juno`_.

Preparing TF-A images
~~~~~~~~~~~~~~~~~~~~~

After building TF-A, the files ``bl1.bin`` and ``fip.bin`` need copying to the
``SOFTWARE/`` directory of the Juno SD card.

Other Juno software information
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Please visit the `Arm Platforms Portal`_ to get support and obtain any other Juno
software information. Please also refer to the `Juno Getting Started Guide`_ to
get more detailed information about the Juno Arm development platform and how to
configure it.

Testing SYSTEM SUSPEND on Juno
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The SYSTEM SUSPEND is a PSCI API which can be used to implement system suspend
to RAM. For more details refer to section 5.16 of `PSCI`_. To test system suspend
on Juno, at the linux shell prompt, issue the following command:

.. code:: shell

    echo +10 > /sys/class/rtc/rtc0/wakealarm
    echo -n mem > /sys/power/state

The Juno board should suspend to RAM and then wakeup after 10 seconds due to
wakeup interrupt from RTC.

--------------

*Copyright (c) 2013-2019, Arm Limited and Contributors. All rights reserved.*

.. _Arm Developer page: https://developer.arm.com/open-source/gnu-toolchain/gnu-a/downloads
.. _Linaro Release: http://releases.linaro.org/members/arm/platforms
.. _Linaro Release 19.06: http://releases.linaro.org/members/arm/platforms/19.06
.. _Linaro instructions: https://git.linaro.org/landing-teams/working/arm/arm-reference-platforms.git/about
.. _Arm Platforms User guide: https://git.linaro.org/landing-teams/working/arm/arm-reference-platforms.git/about/docs/user-guide.rst
.. _Instructions for using Linaro's deliverables on Juno: https://community.arm.com/dev-platforms/w/docs/303/juno
.. _Arm Platforms Portal: https://community.arm.com/dev-platforms/
.. _Development Studio 5 (DS-5): https://developer.arm.com/products/software-development-tools/ds-5-development-studio
.. _arm-trusted-firmware-a project page: https://review.trustedfirmware.org/admin/projects/TF-A/trusted-firmware-a
.. _`Linux Coding Style`: https://www.kernel.org/doc/html/latest/process/coding-style.html
.. _Linux master tree: https://github.com/torvalds/linux/tree/master/
.. _Dia: https://wiki.gnome.org/Apps/Dia/Download
.. _here: psci-lib-integration-guide.rst
.. _Trusted Board Boot: ../design/trusted-board-boot.rst
.. _TB_FW_CONFIG for FVP: ../../plat/arm/board/fvp/fdts/fvp_tb_fw_config.dts
.. _Secure-EL1 Payloads and Dispatchers: ../design/firmware-design.rst#user-content-secure-el1-payloads-and-dispatchers
.. _Firmware Update: ../components/firmware-update.rst
.. _Firmware Design: ../design/firmware-design.rst
.. _mbed TLS Repository: https://github.com/ARMmbed/mbedtls.git
.. _mbed TLS Security Center: https://tls.mbed.org/security
.. _Arm's website: `FVP models`_
.. _FVP models: https://developer.arm.com/products/system-design/fixed-virtual-platforms
.. _Juno Getting Started Guide: http://infocenter.arm.com/help/topic/com.arm.doc.dui0928e/DUI0928E_juno_arm_development_platform_gsg.pdf
.. _PSCI: http://infocenter.arm.com/help/topic/com.arm.doc.den0022d/Power_State_Coordination_Interface_PDD_v1_1_DEN0022D.pdf
.. _Secure Partition Manager Design guide: ../components/secure-partition-manager-design.rst
.. _`Trusted Firmware-A Coding Guidelines`: ../process/coding-guidelines.rst
.. _Library at ROM: ../components/romlib-design.rst