Raspberry Pi Pico - Setting Up FreeRTOS and Configuring an LED Task

Introduction

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You will need the Raspberry Pi Pico C SDK development environment.

This article primarily uses VS Code.

FreeRTOS Setup

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From GitHub - raspberrypi/pico-examples/freertos/,

• FreeRTOS_Kernel_import.cmake
• FreeRTOSConfig_examples_common.h
• FreeRTOSConfig.h

to your project.

Here, FreeRTOSConfig.h references the settings in FreeRTOSConfig_examples_common.h.

Since you need to configure FreeRTOS in CMakeLists.txt, add or modify the following content.

Setting the FreeRTOS-Kernel Environment Variable

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set(FREERTOS_KERNEL_PATH ${USERHOME}/.pico-sdk/FreeRTOS-Kernel CACHE PATH "Path to FreeRTOS Kernel")

Replace ${USERHOME}/.pico-sdk/FreeRTOS-Kernel with your own path.

If you haven’t installed the FreeRTOS kernel yet, download it from here.

https://github.com/FreeRTOS/FreeRTOS-Kernel

Including FreeRTOS Kernel Libraries

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# FREERTOS: include FreeRTOS Kernel libraries
include(FreeRTOS_Kernel_import.cmake)

Linking Common Dependency Libraries

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# pull in common dependencies
target_link_libraries(blink 
    pico_stdlib
    FreeRTOS-Kernel-Heap4
)
if (PICO_CYW43_SUPPORTED)
    target_link_libraries(blink 
    pico_cyw43_arch_none
    FreeRTOS-Kernel-Heap4
)
endif()

After making these changes, compile the project.

Configuring the LED Task

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In the main file, add FreeRTOS.h and task.h after setting up the basic configuration.

#include "FreeRTOS.h"
#include "task.h"

To control the LED, we use the pico_set_led(bool led_on) function from the blink demo.

// Turn the LED on or off
void pico_set_led(bool led_on) {
#if defined(PICO_DEFAULT_LED_PIN)
    // Just set the GPIO on or off
    gpio_put(PICO_DEFAULT_LED_PIN, led_on);
#elif defined(CYW43_WL_GPIO_LED_PIN)
    // Ask the Wi-Fi "driver" to set the GPIO on or off
    cyw43_arch_gpio_put(CYW43_WL_GPIO_LED_PIN, led_on);
#endif
}

The following is the part I wrote myself.

Create a task function called led_task.

void led_task() {
    int rc = pico_led_init();
    hard_assert(rc == PICO_OK);
    while (true) {
        pico_set_led(true);
        vTaskDelay(pdMS_TO_TICKS(1000));
        pico_set_led(false);
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

Here, we set a delay of 1000 ms.

Finally, add the following code to the main function.

int main() {
    stdio_init_all();
    xTaskCreate(led_task, "LED Task", 256, NULL, 1, NULL);
    vTaskStartScheduler();
}

stdio_init_all - Initializes all standard stdio types.

xTaskCreate - Creates a new task.

vTaskStartScheduler - Runs the RTOS scheduler.

The LED flashed successfully every second.