🛠 Premier sketch sur le cœur M4 : le blink qui se flash par ADB

Objectives

Program the Arduino side of the X8: you are programming the Cortex-M4 of the STM32H747XI (up to 240 MHz) from the Arduino IDE, while the Cortex-M7 of the same SoC runs the "normally invisible" bridge firmware that exposes the MCU peripherals to Linux. The main difference from a classic board: the sketch is uploaded via ADB (upload.tool=adb, VID 0x2341 / PID 0x0061, application slot 0x08100000–0x08200000), not via standard serial. You will install the core, flash a blink, and understand the roles of the three embedded systems on the board.

Hardware

• 1 × Arduino Portenta X8 + USB-C data cable (USB 3.0 port preferred)
• Arduino IDE 1.8.10+, Arduino IDE 2.x, or arduino-cli
• Board Manager: core “Arduino Mbed OS Portenta Boards”, then board “Arduino Portenta X8” (arduino:mbed_portenta:portenta_x8)
• The board must be visible to adb devices before any upload (see the getting started tutorial)

Full Code

// blink_m4.ino — coeur Cortex-M4 du STM32H747XI de la Portenta X8
// Carte : "Arduino Portenta X8" (arduino:mbed_portenta:portenta_x8)
// L'upload passe par ADB, pas par un port serie classique.

#include "SerialRPC.h"   // optionnel : monitor serie proxyfie vers Linux

int compteur = 0;

void setup {
  Serial.begin(115200);      // visible cote Linux via le service m4-proxy
  while (!Serial) {}
  pinMode(LED_BUILTIN, OUTPUT);
  Serial.println("Portenta X8 - sketch M4 en vie");
}

void loop {
  digitalWrite(LED_BUILTIN, HIGH);
  delay(500);
  digitalWrite(LED_BUILTIN, LOW);
  delay(500);
  Serial.print("tick ");
  Serial.println(compteur++);
}

Expected Verification

In the IDE, the upload displays progress via adb, then the sketch starts: the LED blinks at 1 Hz. The Serial of this sketch is not a classic USB serial port — it is proxied to Linux by the m4-proxy service (the RPC tutorial will teach you how to read it from a container). Keep an eye on the board: if the upload fails, adb devices must already respond before touching the code.

Common Errors

• Upload fails even though the code compiles: ADB upload requires the board to be seen by adb — under Linux, udev permissions are needed for VID 0x2341; historically, adb has also broken on arm64 hosts (ArduinoCore-mbed issue #492, closed).
• Selecting “Portenta H7” instead of “Portenta X8”: same core family, different target — the X8 has a different bootloader/upload tool (adb).
• Waiting for the classic IDE serial monitor: on the X8, the M4 console goes through SerialRPC/m4-proxy on the Linux side; the standard USB serial monitor is not the documented path.
• Confusing the cores: the M4 is YOUR Arduino core; the M7 of the same SoC runs Arduino’s bridge firmware (do not flash it with the IDE — it is updated via a dedicated procedure, see the firmware tutorial).
• Compilation errors in online examples such as QSPIFBlockDevice not found or WiFiAccessPoint does not name a type: known rot from old examples (ArduinoCore-mbed issues #529 open / #884 closed) — start from the examples in the installed core, not from 2022 blogs.
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