🛠 Zephyr RTOS sur la Nucleo-F401RE : west build, devicetree et west flash

Goals

Build and flash Zephyr RTOS on the Nucleo-F401RE. The board is an in-tree Zephyr target (nucleo_f401re) maintained on main, and the official board doc walks through west build -b nucleo_f401re samples/hello_world + west flash, with output on /dev/ttyACM0. Because the LED comes from the board devicetree, the same blinky source runs on every Nucleo.

Hardware

• 1× Nucleo-F401RE + micro-USB cable
• PC with the Zephyr SDK and the west workspace tool installed (Zephyr Getting Started guide)

Steps

1. Create a Zephyr workspace and initialize main (the board YAML declares 96 KiB RAM / 512 KiB flash).
2. Build the sample: west build -b nucleo_f401re samples/hello_world
3. Flash: west flash — the default runner is the STM32CubeProgrammer runner ; OpenOCD and J-Link runners also work, all driving the on-board ST-LINK over SWD.
4. Open /dev/ttyACM0 (Linux) or the ST-LINK COM port (Windows) at 115200.

Code (devicetree-driven blinky)

#include <zephyr/kernel.h>
#include <zephyr/drivers/gpio.h>

/* led0 = LD2 = PA5 comes from the board DTS, not from this file */
static const struct gpio_dt_spec led = GPIO_DT_SPEC_GET(DT_ALIAS(led0), gpios);

int main(void)
{
    if (!gpio_is_ready_dt(&led)) return -1;
    gpio_pin_configure_dt(&led, GPIO_OUTPUT_ACTIVE);

    while (1) {
        gpio_pin_toggle_dt(&led);
        k_msleep(500);              /* RTOS sleep, not busy-wait */
    }
    return 0;
}

Build it with west build -b nucleo_f401re samples/basic/blinky.

Why Zephyr on this board

• The board doc lists the full peripheral set: 12-bit ADC (16 ch), RTC, 1 advanced + 7 general-purpose timers, 2 watchdogs, 3× USART/UART, 3× I2C, 4× SPI, SDIO, USB OTG FS, DMA, I2S.
• The board YAML ships Arduino-compat GPIO/I2C/SPI bindings (arduino_gpio, arduino_i2c, arduino_spi), so shield-style code can move between the Arduino core and Zephyr.
• k_msleep yields to the kernel — your blink coexists with drivers and threads instead of hogging the CPU.

Expected result

hello_world prints Hello World! nucleo_f401re on the serial console ; blinky pulses LD2 every 500 ms. Same source, same command line, any Nucleo-64 board — only the -b target changes.

Common mistakes

• Leaving CubeProgrammer or a serial monitor open during west flash: the ST-LINK is busy and the runner fails.
• Expecting a bootloader drive: there is none — flashing is SWD through the ST-LINK.
• Following old mbed tutorials: mbed's online services were sunset in July 2026 ; Zephyr (or the Mbed CE fork) is the maintained path.