1 前言
之前写过一篇cmake，不过很简单：CMake小结_cmake ${sources}-CSDN博客
构建系统现在真的太多了，完全学不过来的感觉，meson，gardle，buildroot， Maven。。。我是真的有点放弃治疗了。之前其实CMake主打过一阵，不过那时还忙着GT的事情，所以基本上是混过来的。也没有太认真去看。
最近在看FreeRTOS，用的板子是pico，首当其冲遇到的问题就是编译环境，没想到这里用的也是CMake，前两天尝试增加了一点东西，但是报错很多。看来这次这玩意是绕不开了，结合树莓派的手册，这次就详细再看看吧。有个实际的高手的项目看，也比自己瞎学强多了。。
手册来自：https://github.com/raspberrypi/pico-sdk
具体位置是：https://rptl.io/pico-get-started
2 PICO样例工程
手册里面有一章节专门说到了怎么手动配置一个工程，Manually Create your own Project。因为是官方手册，所以说的也非常详细。
代码如下：
test.c
cpp
#include <stdio.h>
#include "pico/stdlib.h"
#include "hardware/gpio.h"
#include "pico/binary_info.h"
const uint LED_PIN = 25;
int main()
{
bi_decl(bi_program_description("This is a test binary."));
bi_decl(bi_1pin_with_name(LED_PIN, "On-board LED"));
stdio_init_all();
gpio_init(LED_PIN);
gpio_set_dir(LED_PIN, GPIO_OUT);
while (1) {
gpio_put(LED_PIN, 0);
sleep_ms(250);
gpio_put(LED_PIN, 1);
puts("Hello World\n");
sleep_ms(1000);
}
}CMakeLists.txt
bash
cmake_minimum_required(VERSION 3.13)
include(pico_sdk_import.cmake)
project(test_project C CXX ASM)
set(CMAKE_C_STANDARD 11)
set(CMAKE_CXX_STANDARD 17)
pico_sdk_init()
add_executable(test test.c)
pico_enable_stdio_usb(test 1)
pico_enable_stdio_uart(test 1)
pico_add_extra_outputs(test)
target_link_libraries(test pico_stdlib)最后要从pico的sdk中拷贝一个文件过来。
pico_sdk_import.cmake
原始位置是在/pico-sdk/external/pico_sdk_import.cmake
此时结构如下：
创建一个build，cmake..，然后make
对了，这里说个题外话，每次编译的时候，都说找不到picotool，所以编译工具会自己去下载，但是github在国内的稳定性大家是知道的，所以尝尝编译报错都是因为这个下不下来。所以可以先安装picotool。
git clone https://github.com/raspberrypi/picotool.git mkdir build cd build cmake .. make make install
cmake ..
bash
tom@PC-20241221RKUQ:/mnt/e/test/pico/test/build$ cmake ..
Using PICO_SDK_PATH from environment ('/mnt/e/test/pico/pico-sdk')
PICO_SDK_PATH is /mnt/e/test/pico/pico-sdk
Initializing PICO_PLATFORM from environment ('rp2040')
Defaulting target board (PICO_BOARD) to 'pico' since not specified.
Using board configuration from /mnt/e/test/pico/pico-sdk/src/boards/include/boards/pico.h
Pico Platform (PICO_PLATFORM) is 'rp2040'.
-- Defaulting build type to 'Release' since not specified.
Defaulting compiler (PICO_COMPILER) to 'pico_arm_cortex_m0plus_gcc' since not specified.
Configuring toolchain based on PICO_COMPILER 'pico_arm_cortex_m0plus_gcc'
Defaulting PICO_GCC_TRIPLE to 'arm-none-eabi'
-- The C compiler identification is GNU 13.2.1
-- The CXX compiler identification is GNU 13.2.1
-- The ASM compiler identification is GNU
-- Found assembler: /usr/bin/arm-none-eabi-gcc
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/arm-none-eabi-gcc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/arm-none-eabi-g++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
Build type is Release
-- Found Python3: /usr/bin/python3 (found version "3.12.3") found components: Interpreter
TinyUSB available at /mnt/e/test/pico/pico-sdk/lib/tinyusb/src/portable/raspberrypi/rp2040; enabling build support for USB.
BTstack available at /mnt/e/test/pico/pico-sdk/lib/btstack
cyw43-driver available at /mnt/e/test/pico/pico-sdk/lib/cyw43-driver
lwIP available at /mnt/e/test/pico/pico-sdk/lib/lwip
mbedtls available at /mnt/e/test/pico/pico-sdk/lib/mbedtls
-- Configuring done (7.6s)
-- Generating done (6.3s)
-- Build files have been written to: /mnt/e/test/pico/test/buildmake
bash
tom@PC-20241221RKUQ:/mnt/e/test/pico/test/build$ make
[ 1%] Building ASM object pico-sdk/src/rp2040/boot_stage2/CMakeFiles/bs2_default.dir/compile_time_choice.S.o
[ 2%] Linking ASM executable bs2_default.elf
[ 2%] Built target bs2_default
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[ 5%] Building ASM object pico-sdk/src/rp2040/boot_stage2/CMakeFiles/bs2_default_library.dir/bs2_default_padded_checksummed.S.o
[ 5%] Built target bs2_default_library
make[2]: Warning: File 'CMakeFiles/test.dir/depend.make' has modification time 0.5 s in the future
[ 6%] Building C object CMakeFiles/test.dir/test.c.o
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[100%] Linking CXX executable test.elf
make[2]: warning: Clock skew detected. Your build may be incomplete.
[100%] Built target test好了，看来这个cmake里面干的事情还不少。
3 再看CMake
CMake的基本原理这里就不多说了，其实就是一个构建脚本的再抽象。
官网上有一个详细的教程：
CMake Tutorial --- CMake 4.0.0-rc2 Documentation
他家还有一个网课，不过现在貌似是关闭了。
对于CMake的重点是那个CMakeLists.txt，下面列了我觉得最常用几个，完了命令行再看看大体也差不多了。
|---------------------------------------------------------------------------------------|--------------------------------|
| 名称 | 作用 |
| cmake_minimum_required(VERSION <min_version>) | 指定项目所需的最低 CMake 版本 |
| project(<project_name> [LANGUAGES <language>...]) | 定义项目名称和使用的编程语言 |
| add_executable(<target_name> <source_files>...) | 添加一个可执行文件目标，并指定其源文件 |
| add_library(<target_name> [STATIC | SHARED | MODULE] <source_files>...) | 添加一个库目标，可以是静态库、动态库或模块库 |
| target_link_libraries(<target_name> <libraries>...) | 指定目标需要链接的库 |
| include_directories(<dir>...) | 添加头文件搜索路径 |
| target_include_directories(<target_name> <INTERFACE|PUBLIC|PRIVATE> <dir>...) | 为特定目标添加头文件搜索路径 |
| add_subdirectory(<source_dir> [binary_dir]) | 添加子目录，子目录必须包含CMakeLists.txt 文件 |
| set(<variable> <value> [CACHE <type> <docstring> [FORCE]]) | 设置变量的值 |
| add_definitions(<definitions>...) | 添加预处理器定义 |
| add_custom_target(<target_name> [ALL] [command]...) | 添加一个自定义目标，通常用于执行自定义命令 |
| message([<mode>] "message text") | 打印消息，用于调试或信息输出 |
详细的命令说明可以看：cmake-commands(7) --- CMake 4.0.0-rc2 Documentation
4 PICO样例工程分析
因为这次的重心不是代码，所以这里代码就不看了。
重点还是CMakeLists.txt，这次一行一行的过。
bash
cmake_minimum_required(VERSION 3.13)
include(pico_sdk_import.cmake)
project(test_project C CXX ASM)
set(CMAKE_C_STANDARD 11)
set(CMAKE_CXX_STANDARD 17)
pico_sdk_init()
add_executable(test test.c)
pico_enable_stdio_usb(test 1)
pico_enable_stdio_uart(test 1)
pico_add_extra_outputs(test)
target_link_libraries(test pico_stdlib)从列表来看，PICO是自己扩展了不少函数，重点要看的就是include(pico_sdk_import.cmake)，pico_sdk_init()，pico_add_extra_outputs(test)。至于pico_enable_stdio_usb(test 1)，pico_enable_stdio_uart(test 1)感觉就是两个宏定义。
include(pico_sdk_import.cmake)
这个主要是配置pico的路径，如果没有配置PICO_SDK_PATH，会直接从github去下载。真正的初始化，是后面include pico_sdk_init.cmake。在这里，就定义了这个宏ico_sdk_init()。
bash
macro(pico_sdk_init)
if (NOT CMAKE_PROJECT_NAME)
message(WARNING "pico_sdk_init() should be called after the project is created (and languages added)")
endif()
add_subdirectory(${PICO_SDK_PATH} pico-sdk)
endmacro()这里就是包含了pico-sdk里面的第一个CMakeLists.txt。和我们一般使用库不同，一般就是只要头文件，然后静态或者动态链接。这里是相当于你编译一个小程序，实际上也是把整个pico-sdk加进来了的。
至于pico_add_extra_outputs(test)。
这个的定义是在：pico-sdk/src/cmake/on_device.cmake，这个是一个function定义，不是之前的macro。
bash
function(pico_add_extra_outputs TARGET)
# Disassembly will be nonsense for encrypted binaries,
# so disassemble before picotool processing
pico_add_dis_output(${TARGET})
# Picotool processing (signing/encrypting/etc)
# PICO_CMAKE_CONFIG: PICO_NO_PICOTOOL, Disable use/requirement for picotool meaning that UF2 output and signing/hashing and coprocoessor disassembly will all be unavailable, type=bool, default=0, group=build
if (NOT PICO_NO_PICOTOOL)
picotool_postprocess_binary(${TARGET} IS_ENCRYPTED)
endif()
if (PICO_32BIT)
pico_add_hex_output(${TARGET})
endif()
pico_add_bin_output(${TARGET})
pico_add_map_output(${TARGET})
# PICO_CMAKE_CONFIG: PICO_NO_TARGET_NAME, Don't define PICO_TARGET_NAME, type=bool, default=0, group=build
# PICO_BUILD_DEFINE: PICO_TARGET_NAME, Name of the build target being compiled (unless PICO_NO_TARGET_NAME set in build), type=string, default=target name, group=build
if (NOT PICO_NO_TARGET_NAME)
target_compile_definitions(${TARGET} PRIVATE
PICO_TARGET_NAME="${TARGET}"
)
endif()
if (PICO_SYMLINK_ELF_AS_FILENAME)
add_custom_target(${TARGET}_symlinked)
add_dependencies(${TARGET}_symlinked ${TARGET})
add_custom_command(TARGET ${TARGET}_symlinked POST_BUILD
COMMAND rm -f "${PICO_SYMLINK_ELF_AS_FILENAME}"
COMMAND ln -s -r $<TARGET_FILE:${TARGET}> "${PICO_SYMLINK_ELF_AS_FILENAME}"
COMMENT "Symlinking from ${PICO_SYMLINK_ELF_AS_FILENAME} to ${TARGET}"
)
endif ()
# PICO_CMAKE_CONFIG: PICO_NO_UF2, Disable UF2 output, type=bool, default=0, group=build
if (NOT (PICO_NO_UF2 OR PICO_NO_PICOTOOL))
pico_add_uf2_output(${TARGET})
endif()
endfunction()这里还包含了很多个其它的函数，大体就是将编译的程序最后转换成可以在板子上运行的uf2格式。
5 增加FreeRTOS支持
回到之前的那一篇：RTOS基础1（FreeRTOS+树莓派PICO环境）-CSDN博客
看看里面加了什么。
增加了自己的一个freertos，还有一个pico_sdk_import.cmake。
它的CMakeLists.txt是这样的
cmake_minimum_required(VERSION 3.12)
include(pico_sdk_import.cmake)
project(Pico-FreeRTOS)
pico_sdk_init()
add_subdirectory(freertos)
add_subdirectory(ProjectFiles)
多出来的一句就是add_subdirectory(freertos)
再看看子CMakeLists.txt，也就是ProjectFiles里面的。
add_executable(blink main.c)
pico_sdk_init()
target_link_libraries(blink pico_stdlib freertos)
pico_add_extra_outputs(blink)
其实就是一个，target_link_libraries(blink pico_stdlib freertos)，增加链接freertos的库就可以了。
好吧，好像确实也不难哈。明天再继续试试。。。
6 小结
CMake的东西确实比我想的要多多了。
个人觉得，实际上它有两个很大的作用。
1 就是跨平台的构建。比如说一套编译脚本，可以在linux，苹果，windows下都搞定了。这个之前都知道。
2 针对自动化构建，做了很多内容。比如创建宏或者函数，处理github下载这些，这些以前的makefile确实解决这些不那么方便。这部分CMake几乎是增加了半套语言。。。当然，如果能换成python语言就更好了。