Build and configuration system

The nRF Connect SDK build and configuration system is based on the one from Zephyr, with some additions.

Zephyr’s build and configuration system

Zephyr’s build and configuration system uses the following building blocks as a foundation:

• CMake, the cross-platform build system generator.

• Kconfig, a powerful configuration system also used in the Linux kernel.

• Devicetree, a hardware description language that is used to describe the hardware that the nRF Connect SDK is meant to run on.

Since the build and configuration system used by the nRF Connect SDK comes from Zephyr, references to the original Zephyr documentation are provided here in order to avoid duplication. See the following links for information about the different building blocks mentioned above:

• Application Development is a complete guide to application development with Zephyr, including the build and configuration system.

• Build System (CMake) describes in-depth the usage of CMake for Zephyr-based applications.

• Kconfig Configuration contains a guide for Kconfig usage in applications.

• Set devicetree overlays explains how to use devicetree and its overlays to customize an application’s devicetree.

• Board Porting Guide is a complete guide to porting Zephyr to your own board.

nRF Connect SDK additions

The nRF Connect SDK adds some functionality on top of the Zephyr build and configuration system. Those additions are automatically included into the Zephyr build system using a Zephyr Build Configuration CMake packages.

You must be aware of these additions when you start writing your own applications based on this SDK.

• The Kconfig option CONFIG_WARN_EXPERIMENTAL is enabled by default. It gives warnings at CMake configure time if any experimental feature is enabled.

  For example, when building a sample that enables CONFIG_BT_EXT_ADV, the following warning is printed at CMake configure time:

  warning: Experimental symbol BT_EXT_ADV is enabled.
  

  For more information, see Software maturity levels.

• The nRF Connect SDK provides an additional boilerplate.cmake file that is automatically included when using the Zephyr CMake package in the CMakeLists.txt file of your application:

  find_package(Zephyr HINTS $ENV{ZEPHYR_BASE})
  

• The nRF Connect SDK allows you to create custom build type files instead of using a single prj.conf file.

• The nRF Connect SDK build system extends Zephyr’s with support for multi-image builds. You can find out more about these in the Multi-image builds section.

• The nRF Connect SDK adds a Partition Manager, responsible for partitioning the available flash memory.

• The nRF Connect SDK build system generates zip files containing binary images and a manifest for use with nRF Cloud FOTA.

nRF Connect SDK configuration tools

The nRF Connect for VS Code extension provides the following configuration tools for the build system components:

• For CMake, the build configuration management.

• For Devicetree, the Devicetree Visual Editor.

• For Kconfig, the Kconfig GUI.

Building FOTA images

The nRF Connect SDK build system places output images in the <build folder>/zephyr folder. These images are then used for updates from a cloud served (for example, nRF Cloud).

If CONFIG_BOOTLOADER_MCUBOOT is set, the build system creates the dfu_application.zip file containing files app_update.bin and manifest.json. When you set the CONFIG_BOOT_BUILD_DIRECT_XIP_VARIANT Kconfig option, the build system creates a secondary slot variant of the app_update.bin, named mcuboot_secondary_app_update.bin, and includes it in the dfu_application.zip file. The CONFIG_BOOT_BUILD_DIRECT_XIP_VARIANT Kconfig option and the MCUboot direct-xip mode are currently supported only on the single-core devices such as the nRF52 Series. If you have also set the options CONFIG_IMG_MANAGER and CONFIG_MCUBOOT_IMG_MANAGER, the application will be able to process FOTA updates. If you have set the options CONFIG_SECURE_BOOT and CONFIG_BUILD_S1_VARIANT, a similar file dfu_mcuboot.zip will also be created. You can use this file to perform FOTA updates of MCUboot itself.

The app_update.bin file is a signed version of your application. The signature matches to what MCUboot expects and allows this file to be used as an update. The build system creates a manifest.json file using information in the zephyr.meta output file. This includes the Zephyr and nRF Connect SDK git hashes for the commits used to build the application. If your working tree contains uncommitted changes, the build system adds the suffix -dirty to the relevant version field.

Output build files

The building process produces each time an image file.

The image file can refer to an executable, a program, or an ELF file. As one of the last build steps, the linker processes all object files by locating code, data, and symbols in sections in the final ELF file. The linker replaces all symbol references to code and data with addresses. A symbol table is created which maps addresses to symbol names, which is used by debuggers. When an ELF file is converted into another format, such as HEX or binary, the symbol table is lost.

Depending on the application and the SoC, you can use one or several images.

The following table lists build files that can be generated as output when building firmware for supported build targets. The table includes files for single-core and multi-core programming scenarios for both Visual Studio Code and command line building methods. Which files you are going to use depends on the application configuration and not directly on the type of SoC you are using. The following scenarios are possible:

• Single-image - Only one firmware image file is generated for a single core.

• Multi-image - Two or more firmware image files are generated for a single core. You can read more about this scenario in Multi-image builds.

• Multi-core - Two or more firmware image files are generated for two or more cores.

File	Description	Programming scenario
zephyr.hex	Default full image. In a multi-image build, several zephyr.hex files are generated, one for each image.	Programming build targets with NSPE or single-image. Testing DFU procedure with nrfjprog (programming directly to device).
merged.hex	The result of merging all zephyr.hex files for all images for a core in a multi-image build. Used by Nordic Semiconductor’s build targets in single-core multi-image builds. In multi-core builds, several merged_<image_name>.hex fields are generated, where <image-name> indicates the core.	Programming multi-core application. Testing DFU procedure with nrfjprog (programming directly to device).
merged_domains.hex	The result of merging all merged.hex files for all cores or processing environments (merged.hex for the application core and merged.hex or zephyr.hex for the network core).	Programming SPE-only and multi-core build targets. Testing DFU procedure with nrfjprog (programming directly to device).
tfm_s.hex	Secure firmware image created by the TF-M build system in the background of the Zephyr build. It is used together with the zephyr.hex file, which is intended for the Non-Secure Processing Environment (NSPE). Located in build/tfm/bin.	Programming SPE-only and multi-core build targets.
app_update.bin	Application core update file used to create dfu_application.zip for multi-core DFU. Can also be used standalone for a single-image DFU. Contains the signed version of the application. This file is transferred in the real-life update procedure, as opposed to HEX files that are transferred with nrfjprog when emulating an update procedure. Compatible with MCUboot.	DFU process for single-image build targets and the application core of the multi-core build targets.
app_signed.hex	HEX file variant of the app_update.bin file. Can also be used standalone for a single-image DFU. Contains the signed version of the application. Compatible with MCUboot.	Programming single-image build targets and the application core of the multi-core build targets.
mcuboot_secondary_app_update.bin	Secondary slot variant of the app_update.bin file. Compatible with MCUboot in the direct-xip mode.	DFU process for single-core build targets.
mcuboot_secondary_app_signed.hex	Secondary slot variant of the app_signed.hex file. Compatible with MCUboot in the direct-xip mode.	Programming single-core build targets.
net_core_app_update.bin	Network core update file used to create dfu_application.zip. This file is transferred in the real-life update procedure, as opposed to HEX files that are transferred with nrfjprog when emulating an update procedure.	DFU process for the network core of multi-core build targets.
dfu_application.zip	Zip file containing both the MCUboot-compatible update image for one or more cores and a manifest describing its contents.	DFU process for both single-core and multi-core applications.
matter.ota	Matter-specific OTA image that contains a Matter-compliant header and a DFU multi-image package that bundles user-selected firmware images.	DFU over Matter for both single-core and multi-core applications.
<file_name>.zigbee	Zigbee-specific OTA image that contains the Zigbee application with the Zigbee OTA header used for providing information about the image to the OTA server. The <file_name> includes manufacturer’s code, image type, file version, and comment (customizable by user, sample name by default). For example: 127F-0141-01020003-light_switch.zigbee.	DFU over Zigbee for both single-core and multi-core applications in the nRF Connect SDK v2.0.0 and later.

MCUboot output build files

File	Description
dfu_application.zip	Contains the following: The MCUboot-compatible update image for one or more cores when MCUboot is not in the direct-xip mode and a manifest describing its contents (all related *.bin files and a manifest.json file). The MCUboot-compatible update image for the primary and secondary slots when MCUboot is in the direct-xip mode and manifest describing its contents (all related *.bin files and a manifest.json file).
dfu_mcuboot.zip	Contains two versions of MCUboot linked against different address spaces corresponding to slot0 (s0) and slot1 (s1) and a manifest JSON file describing their MCUboot version number (MCUBOOT_IMGTOOL_SIGN_VERSION), NSIB version number (FW_INFO), board type. This file can be used by FOTA servers (for example, nRF Cloud) to serve both s0 and s1 to the device. The device can then select the firmware file for the slot that is currently not in use.
app_update.bin	Signed variant of the firmware in binary format (as opposed to HEX). It can be uploaded to a server as a FOTA image.
signed_by_mcuboot_and_b0_s0_image_update.bin	MCUboot update image for s0 signed by both MCUboot and NSIB. The MCUboot signature is used by MCUboot to verify the integrity of the image before swapping and the NSIB signature is used by NSIB before booting the image.
signed_by_mcuboot_and_b0_s1_image_update.bin	MCUboot update image for s1 signed by both MCUboot and NSIB. The MCUboot signature is used by MCUboot to verify the integrity of the image before swapping and the NSIB signature is used by NSIB before booting the image.
app_to_sign.bin	Unsigned variant of the firmware in binary format.
app_signed.hex	Signed variant of the firmware in the HEX format. This HEX file is linked to the same address as the application. Programming this file to the device will overwrite the existing application. It will not trigger a DFU procedure.
app_test_update.hex	Same as app_signed.hex except that it contains metadata that instructs MCUboot to test this firmware upon boot. As app_signed.hex, this HEX file is linked against the same address as the application. Programming this file to the device will overwrite the existing application. It will not trigger a DFU procedure.
app_moved_test_update.hex	Same as app_test_update.hex except that it is linked to the address used to store the upgrade candidates. When this file is programmed to the device, MCUboot will trigger the DFU procedure upon reboot.
signed_by_mcuboot_and_b0_s0_image_moved_test_update.hex	Moved to MCUboot secondary slot address space.
signed_by_mcuboot_and_b0_s0_image_test_update.hex	Directly overwrites s0.
mcuboot_secondary_app_update.bin	Secondary slot variant of the app_update.bin file intended for use when MCUboot is in the direct-xip mode. Created when the CONFIG_BOOT_BUILD_DIRECT_XIP_VARIANT Kconfig option is enabled.
mcuboot_secondary_app_signed.hex	Secondary slot variant of the app_signed.hex file intended for use when MCUboot is in the direct-xip mode. Created when the CONFIG_BOOT_BUILD_DIRECT_XIP_VARIANT Kconfig option is enabled.
mcuboot_secondary_app_test_update.hex	Secondary slot variant of the app_test_update.hex file intended for use when MCUboot is in the direct-xip mode. Created when the CONFIG_BOOT_BUILD_DIRECT_XIP_VARIANT Kconfig option is enabled.
mcuboot_secondary_app_to_sign.bin	Secondary slot variant of the app_to_sign.bin file intended for use when MCUboot is in the direct-xip mode. Created when the CONFIG_BOOT_BUILD_DIRECT_XIP_VARIANT Kconfig option is enabled.

Other output build files

The following table lists secondary build files that can be generated when building firmware, but are only used to create the final output build files listed in the table above.

File	Description
zephyr.elf	An ELF file for the image that is being built. Can be used for debugging purposes.
zephyr.meta	A file with the Zephyr and nRF Connect SDK git hashes for the commits used to build the application.
tfm_s.elf	An ELF file for the TF-M image that is being built. Can be used for debugging purposes.
manifest.json	Output artifact that uses information from the zephyr.meta output file.
dfu_multi_image.bin	Multi-image package that contains a CBOR manifest and a set of user-selected update images, such as firmware images for different cores. Used for DFU purposes by Matter and Zigbee protocols.
signed_by_b0_s0_image.bin	Intermediate file only signed by NSIB.
signed_by_b0_s1_image.bin	Intermediate file only signed by NSIB.