from https://discourse.cmake.org/t/external-project-dependency/8862
Downloads nRF5 SDK and builds static library libsystem_nrf54.a
CMake FetchContent ignore build system
CMake FetchContent and ExternalProject bring remote projects into the top-level project to avoid making a monorepo or vendoring code into the top-level project. With FetchContent, the source code is retrieved at CMake configure time, allowing one to ignore the subproject build system and / or use only specific source files.
An example of this is using nRF5 SDK, which is a large project, but one may only wish to use a single source file and header as in this example:
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| cmake_minimum_required(VERSION 3.14...3.27) | |
| if(CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR) | |
| message(FATAL_ERROR "please use out-of-source build | |
| cmake -Bbuild") | |
| endif() | |
| project(otherSource LANGUAGES C) | |
| set(NRF_SDK_NAME nRF5_SDK_17.1.0_ddde560) | |
| if(NOT DEFINED FETCHCONTENT_QUIET) | |
| set(FETCHCONTENT_QUIET FALSE) | |
| endif() | |
| set(CMAKE_TLS_VERIFY true) | |
| # placeholders | |
| set(BOARD_TARGET NRF52805_XXAA) | |
| include(FetchContent) | |
| # https://www.nordicsemi.com/Products/Development-software/nRF5-SDK/Download | |
| set(NRF_SDK_DOWNLOAD_URL | |
| https://www.nordicsemi.com/-/media/Software-and-other-downloads/SDKs/nRF5/Binaries/${NRF_SDK_NAME}.zip | |
| ) | |
| # setting hash avoid redownload of big archive on each CMake configure, | |
| # and provides a way to check if the archive is corrupted | |
| set(NRF_SDK_DOWNLOAD_SHA256 5bfe38e744c39fd7f30e10077ba12df306ef91f368894795d6a3e7a62dc68061) | |
| FetchContent_Declare(nrf5_sdk | |
| URL ${NRF_SDK_DOWNLOAD_URL} | |
| URL_HASH SHA256=${NRF_SDK_DOWNLOAD_SHA256} | |
| TLS_VERIFY ${CMAKE_TLS_VERIFY} | |
| INACTIVITY_TIMEOUT 60 | |
| ) | |
| FetchContent_Populate(nrf5_sdk) | |
| # auto-ignore build dir | |
| file(GENERATE OUTPUT .gitignore CONTENT "*") | |
| # main program | |
| add_library(system_nrf54 ${nrf5_sdk_SOURCE_DIR}/modules/nrfx/mdk/system_nrf52.c) | |
| target_include_directories(system_nrf54 PRIVATE ${nrf5_sdk_SOURCE_DIR}/components/toolchain/cmsis/include) | |
| target_compile_definitions(system_nrf54 PRIVATE ${BOARD_TARGET}) |