RTOS基础1（FreeRTOS+树莓派PICO环境）

原创已于 2025-02-21 20:00:00 修改 · 778 阅读

4 ·

CC 4.0 BY-SA版权

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#rtos #嵌入式

于 2025-02-05 16:45:36 首次发布

RTOS 专栏收录该内容

4 篇文章

订阅专栏

1 前置阅读

最近遇到很多需要RTOS的项目，正好也有点时间，自己也有点兴趣，开发板环境啥的都有现成的，所以也就学习一下。

参考文档：

读完FreeRTOS内核源码，需要多久？

有哪些情况下是RTOS满足不了需求，必须得上嵌入式Linux系统的？

如何进行 RTOS内核的裁剪与优化？

============================

2 环境搭建和编译

这次的硬件是树莓派PICO，还有FreeRTOS，本来是打算直接下载PICO SDK还有FreeRTOS，然后自己写一个例程进行单独编译的，但是在腾讯云上实在有太多的被墙和下载的问题：

没办法，继续看一下别人是怎么解决的，后面看到树莓派热心大佬的一个帖子：

https://forums.raspberrypi.com/viewtopic.php?t=334622

还有一个懒人包：

https://github.com/LearnEmbeddedSystems/rp2040-freertos-project

里面的例程也是经典的LED眨眼，直接下下来，在ProjectFiles中创建make。配置好PICO的SDK，就可以直接用了。

ubuntu@VM-8-10-ubuntu:~/test/freertos/rp2040-freertos-project/build$ export PICO_SDK_PATH=/home/ubuntu/test/freertos/pico-sdk/
ubuntu@VM-8-10-ubuntu:~/test/freertos/rp2040-freertos-project/build$ cmake ..
Using PICO_SDK_PATH from environment ('/home/ubuntu/test/freertos/pico-sdk/')
PICO_SDK_PATH is /home/ubuntu/test/freertos/pico-sdk
Defaulting platform (PICO_PLATFORM) to 'rp2040' since not specified.
Defaulting target board (PICO_BOARD) to 'pico' since not specified.
Using board configuration from /home/ubuntu/test/freertos/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
-- 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
-- The ASM compiler identification is GNU
-- Found assembler: /usr/bin/arm-none-eabi-gcc
Build type is Release
-- Found Python3: /usr/bin/python3 (found version "3.12.3") found components: Interpreter
TinyUSB available at /home/ubuntu/test/freertos/pico-sdk/lib/tinyusb/src/portable/raspberrypi/rp2040; enabling build support for USB.
BTstack available at /home/ubuntu/test/freertos/pico-sdk/lib/btstack
cyw43-driver available at /home/ubuntu/test/freertos/pico-sdk/lib/cyw43-driver
lwIP available at /home/ubuntu/test/freertos/pico-sdk/lib/lwip
mbedtls available at /home/ubuntu/test/freertos/pico-sdk/lib/mbedtls
CMake Warning at /home/ubuntu/test/freertos/pico-sdk/tools/Findpicotool.cmake:28 (message):
  No installed picotool with version 2.1.0 found - building from source

  It is recommended to build and install picotool separately, or to set
  PICOTOOL_FETCH_FROM_GIT_PATH to a common directory for all your SDK
  projects
Call Stack (most recent call first):
  /home/ubuntu/test/freertos/pico-sdk/tools/CMakeLists.txt:138 (find_package)
  /home/ubuntu/test/freertos/pico-sdk/tools/CMakeLists.txt:485 (pico_init_picotool)
  /home/ubuntu/test/freertos/pico-sdk/src/cmake/on_device.cmake:57 (picotool_postprocess_binary)
  ProjectFiles/CMakeLists.txt:6 (pico_add_extra_outputs)


Downloading Picotool
-- Configuring done (6.8s)
-- Generating done (0.1s)
-- Build files have been written to: /home/ubuntu/test/freertos/rp2040-freertos-project/build
ubuntu@VM-8-10-ubuntu:~/test/freertos/rp2040-freertos-project/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
[  3%] Generating bs2_default.bin
[  4%] Generating bs2_default_padded_checksummed.S
[  6%] Building ASM object pico-sdk/src/rp2040/boot_stage2/CMakeFiles/bs2_default_library.dir/bs2_default_padded_checksummed.S.o
[  6%] Built target bs2_default_library
[  7%] Building C object freertos/CMakeFiles/freertos.dir/FreeRTOS-Kernel/event_groups.c.o
[  8%] Building C object freertos/CMakeFiles/freertos.dir/FreeRTOS-Kernel/list.c.o
[  9%] Building C object freertos/CMakeFiles/freertos.dir/FreeRTOS-Kernel/queue.c.o
[ 11%] Building C object freertos/CMakeFiles/freertos.dir/FreeRTOS-Kernel/stream_buffer.c.o
[ 12%] Building C object freertos/CMakeFiles/freertos.dir/FreeRTOS-Kernel/tasks.c.o
[ 13%] Building C object freertos/CMakeFiles/freertos.dir/FreeRTOS-Kernel/timers.c.o
[ 14%] Building C object freertos/CMakeFiles/freertos.dir/FreeRTOS-Kernel/portable/MemMang/heap_3.c.o
[ 16%] Building C object freertos/CMakeFiles/freertos.dir/FreeRTOS-Kernel/portable/GCC/ARM_CM0/port.c.o
[ 17%] Linking C static library libfreertos.a
[ 17%] Built target freertos
[ 17%] Built target picotoolForceReconfigure
[ 18%] Creating directories for 'picotoolBuild'
[ 19%] No download step for 'picotoolBuild'
[ 20%] No update step for 'picotoolBuild'
[ 22%] No patch step for 'picotoolBuild'
[ 23%] Performing configure step for 'picotoolBuild'
Not searching for unused variables given on the command line.
-- The C compiler identification is GNU 13.3.0
-- The CXX compiler identification is GNU 13.3.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - 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/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
.//home/ubuntu/test/freertos/rp2040-freertos-project/build/_deps/picotool/
-- Using the single-header code from /home/ubuntu/test/freertos/rp2040-freertos-project/build/_deps/picotool-src/lib/nlohmann_json/single_include/
CMake Deprecation Warning at /home/ubuntu/test/freertos/pico-sdk/lib/mbedtls/CMakeLists.txt:23 (cmake_minimum_required):
  Compatibility with CMake < 3.5 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.


-- Found Python3: /usr/bin/python3 (found version "3.12.3") found components: Interpreter
-- Performing Test C_COMPILER_SUPPORTS_WFORMAT_SIGNEDNESS
-- Performing Test C_COMPILER_SUPPORTS_WFORMAT_SIGNEDNESS - Success
PICOTOOL_NO_LIBUSB is set - no USB support will be built
-- Configuring done (1.0s)
-- Generating done (0.1s)
-- Build files have been written to: /home/ubuntu/test/freertos/rp2040-freertos-project/build/_deps/picotool-build
[ 24%] Performing build step for 'picotoolBuild'
[ 67%] Built target mbedcrypto
[ 76%] Built target mbedx509
[ 86%] Built target mbedtls
[ 88%] Built target errors
[ 89%] Built target elf
[ 92%] Built target bintool
[ 94%] Built target elf2uf2
[100%] Built target picotool
[ 25%] Performing install step for 'picotoolBuild'
[ 67%] Built target mbedcrypto
[ 76%] Built target mbedx509
[ 86%] Built target mbedtls
[ 88%] Built target errors
[ 89%] Built target elf
[ 92%] Built target bintool
[ 94%] Built target elf2uf2
[100%] Built target picotool
Install the project...
-- Install configuration: "Release"
[ 27%] Performing test step for 'picotoolBuild'
picotool v2.1.1-develop (Linux, GNU-13.3.0, Release)
[ 28%] Completed 'picotoolBuild'
[ 28%] Built target picotoolBuild
[ 29%] Building C object ProjectFiles/CMakeFiles/blink.dir/main.c.o
[ 30%] Building C object ProjectFiles/CMakeFiles/blink.dir/home/ubuntu/test/freertos/pico-sdk/src/rp2_common/pico_stdlib/stdlib.c.o
[ 32%] Building C object ProjectFiles/CMakeFiles/blink.dir/home/ubuntu/test/freertos/pico-sdk/src/rp2_common/hardware_gpio/gpio.c.o
[ 33%] Building C object ProjectFiles/CMakeFiles/blink.dir/home/ubuntu/test/freertos/pico-sdk/src/rp2040/pico_platform/platform.c.o
[ 34%] Building C object ProjectFiles/CMakeFiles/blink.dir/home/ubuntu/test/freertos/pico-sdk/src/rp2_common/pico_platform_panic/panic.c.o
[ 35%] Building C object ProjectFiles/CMakeFiles/blink.dir/home/ubuntu/test/freertos/pico-sdk/src/common/hardware_claim/claim.c.o
[ 37%] Building C object ProjectFiles/CMakeFiles/blink.dir/home/ubuntu/test/freertos/pico-sdk/src/rp2_common/hardware_sync/sync.c.o
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[ 95%] Building ASM object ProjectFiles/CMakeFiles/blink.dir/home/ubuntu/test/freertos/pico-sdk/src/rp2_common/pico_crt0/crt0.S.o
[ 96%] Building C object ProjectFiles/CMakeFiles/blink.dir/home/ubuntu/test/freertos/pico-sdk/src/rp2_common/pico_clib_interface/newlib_interface.c.o
[ 97%] Building C object ProjectFiles/CMakeFiles/blink.dir/home/ubuntu/test/freertos/pico-sdk/src/rp2_common/pico_stdio/stdio.c.o
[ 98%] Building C object ProjectFiles/CMakeFiles/blink.dir/home/ubuntu/test/freertos/pico-sdk/src/rp2_common/pico_stdio_uart/stdio_uart.c.o
[100%] Linking CXX executable blink.elf
[100%] Built target blink

生成物如下：

其中PICO要的就是blink.uf2这个文件。直接按住树莓派的BOOTSEL启动，将blink.uf2文件拷贝进去新出现的文件夹，就可以看到效果了。

3 代码阅读

代码结构如下：

其中build是自己建的。项目文件是在ProjectFiles里面。就是两个，CMakeLists.txt和main.c。这次主要关注项目代码。

BTW：cmake之前很简单写过，可以参见：CMake小结_外层cmakelists和内层cmakelists-优快云博客

CMakeLists.txt

add_executable(blink
        main.c
)

target_link_libraries(blink pico_stdlib freertos)
pico_add_extra_outputs(blink)

这里指定了blink的源代码main.c，然后链接的静态库pico_stdlib和freertos，最后是增加uf2的输出。

pico_stdlib，定义在pico-sdk\src\rp2_common\pico_stdlib\CMakeLists.txt（真感觉现在的新库cmake都用得来飞起。。。）

if (NOT TARGET pico_stdlib)
    pico_add_impl_library(pico_stdlib)
    target_sources(pico_stdlib INTERFACE
            ${CMAKE_CURRENT_LIST_DIR}/stdlib.c
    )

    set(PICO_STDLIB_LIBRARIES
            hardware_gpio
            hardware_uart
            hardware_divider
            pico_time
            pico_util
            pico_platform
            pico_runtime
            pico_stdio
    )
    foreach(LIB IN LISTS PICO_STDLIB_LIBRARIES)
        if (TARGET ${LIB})
            pico_mirrored_target_link_libraries(pico_stdlib INTERFACE ${LIB})
        endif()
    endforeach()
endif()

freerots目标定义在freerots根目录的CMakelists.txt如下：

set(PICO_SDK_FREERTOS_SOURCE FreeRTOS-Kernel)

add_library(freertos
    ${PICO_SDK_FREERTOS_SOURCE}/event_groups.c
    ${PICO_SDK_FREERTOS_SOURCE}/list.c
    ${PICO_SDK_FREERTOS_SOURCE}/queue.c
    ${PICO_SDK_FREERTOS_SOURCE}/stream_buffer.c
    ${PICO_SDK_FREERTOS_SOURCE}/tasks.c
    ${PICO_SDK_FREERTOS_SOURCE}/timers.c
    ${PICO_SDK_FREERTOS_SOURCE}/portable/MemMang/heap_3.c
    ${PICO_SDK_FREERTOS_SOURCE}/portable/GCC/ARM_CM0/port.c
)

看着好像就是几个文件。。。这么少吗？后面抽时间再多读读。。。

pico_add_extra_outputs定义如下：

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()

就是把bin转成uf2格式。感觉像是picotool里面的elf2uf2，不过现在没有证据，以后有时间再看看。。。

main.c如下：

#include <FreeRTOS.h>
#include <task.h>
#include <stdio.h>
#include "pico/stdlib.h"


void led_task()
{   
    const uint LED_PIN = PICO_DEFAULT_LED_PIN;
    gpio_init(LED_PIN);
    gpio_set_dir(LED_PIN, GPIO_OUT);
    while (true) {
        gpio_put(LED_PIN, 1);
        vTaskDelay(100);
        gpio_put(LED_PIN, 0);
        vTaskDelay(100);
    }
}

int main()
{
    stdio_init_all();

    xTaskCreate(led_task, "LED_Task", 256, NULL, 1, NULL);
    vTaskStartScheduler();

    while(1){};
}

可以看到。Freertos的使用还是很简单的。

stdio_init_all()是pico的初始化。

xTaskCreate的操作很类似增加线程，但是里面的API要使用xtask和vtask这几个。然后使用vTaskStartScheduler打开调度器。

最后一个while(1)死循环。

进一步参考：Build your first FreeRTOS project - FreeRTOS™

4 参考

如何用树莓派 Pico 学习 RTOS？

树莓派 Pico 使用 RP2040 微控制器，基于 ARM Cortex-M0+ 内核，支持各种 RTOS（实时操作系统）。如果你想学习 RTOS，Pico 是一个很好的平台，以下是系统学习路径：

1. 选择合适的 RTOS

常见的 RTOS 选项：

FreeRTOS（最流行，学习资料多）
RT-Thread（国产 RTOS，适合 IoT）
Zephyr（适用于物联网和工业）
ChibiOS（轻量级，适合小型 MCU）

推荐：FreeRTOS 最适合作为入门 RTOS，官方支持好，教程多，使用广泛。

2. 准备开发环境

硬件

Raspberry Pi Pico
Micro-USB 线
LED、按钮、传感器（扩展实验）

软件

CMake + Ninja + ARM GCC（官方推荐）
VS Code + Pico SDK（推荐）
或者 Keil / IAR（传统嵌入式开发工具）

3. 安装 FreeRTOS 并配置开发环境

(1) 下载 FreeRTOS
git clone https://github.com/FreeRTOS/FreeRTOS-Kernel.git
或者使用官方仓库：
git clone --recurse-submodules https://github.com/FreeRTOS/FreeRTOS.git
(2) 安装 Raspberry Pi Pico SDK
git clone -b master https://github.com/raspberrypi/pico-sdk.git
cd pico-sdk
git submodule update --init
export PICO_SDK_PATH=$PWD
(3) 配置 FreeRTOS 任务调度器

在 FreeRTOSConfig.h 中修改：
#define configUSE_PREEMPTION                    1
#define configUSE_TIME_SLICING                  1
#define configCPU_CLOCK_HZ                      (125000000) // RP2040 125MHz
#define configTICK_RATE_HZ                      (1000)
#define configMAX_PRIORITIES                    (5)
#define configMINIMAL_STACK_SIZE                (configSTACK_DEPTH_TYPE)128
#define configTOTAL_HEAP_SIZE                   ((size_t)(16 * 1024))
4. 编写一个 FreeRTOS 任务

创建 main.c，写入以下代码：
#include <FreeRTOS.h>
#include <task.h>
#include <stdio.h>
#include "pico/stdlib.h"

void Task1(void *pvParameters) {
    while (1) {
        printf("Task 1 running...\n");
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

void Task2(void *pvParameters) {
    while (1) {
        printf("Task 2 running...\n");
        vTaskDelay(pdMS_TO_TICKS(500));
    }
}

int main() {
    stdio_init_all();
    xTaskCreate(Task1, "Task 1", 256, NULL, 1, NULL);
    xTaskCreate(Task2, "Task 2", 256, NULL, 1, NULL);
    vTaskStartScheduler();
    while (1);
}
说明

Task1 每 1000ms 运行一次
Task2 每 500ms 运行一次
vTaskStartScheduler() 启动任务调度器

5. 编译 & 运行

(1) 编译代码
mkdir build
cd build
cmake ..
make -j4
(2) 烧录到 Pico

进入 BOOTSEL 模式（按住 BOOTSEL 按钮，插入 USB）
拷贝生成的 .uf2 文件到 Pico

(3) 观察输出

使用 minicom 或 screen 读取串口输出：
screen /dev/ttyUSB0 115200
6. 进阶学习

✅ 任务同步 & 互斥

队列（Queue）: 任务间通信
信号量（Semaphore）：资源管理
互斥量（Mutex）：防止数据竞争

✅ 中断处理

使用 ISR-safe API，如 xQueueSendFromISR()

✅ 低功耗管理

Tickless Idle 模式降低功耗

✅ 移植 & 设备驱动

在 FreeRTOS 上移植 I2C/SPI/UART 设备驱动

✅ 联网 & 远程控制

结合 LWIP（轻量级 TCP/IP） 使 Pico 具备联网功能

7. 推荐学习资源

📚 书籍

《Mastering FreeRTOS》
《嵌入式实时操作系统开发》
《实时操作系统（RTOS）基础》

🎥 视频

YouTube - FreeRTOS for Beginners

📂 官方文档

FreeRTOS 官方文档
Pico SDK 文档

总结

🔹 用 Raspberry Pi Pico 学习 FreeRTOS 是个很好的选择！ 🔹 从简单的任务调度开始，再深入学习任务间通信、中断管理、功耗优化 🔹 Pico 的双核支持，适合研究 FreeRTOS SMP（多核调度）