🛠 Pont série entre le MCU Arduino et le SoC x86

Objectives

Understand the internal communication channel of the board: the ATmega32U4 is a real Arduino Leonardo that enumerates on a virtual COM port connected to the x86 processor. This is the channel used internally by pinpong/Firmata; here we repurpose it with our own protocol: a C++ sketch on the MCU side that sends timestamped measurements, and a Python script on the Linux side that reads them using pyserial. By the end, you will master both languages of the board (C++ on the MCU, Python on the SoC) and the bridge between them.

Hardware

• LattePanda 3 Delta running Ubuntu 22.04 (or Windows)
• Arduino IDE (board type Arduino Leonardo) to flash the embedded MCU; use the board's Arduino reset button to enter the bootloader
• pip install pyserial on the Linux side
• LED on D13 (from tutorial 1) for a meaningful message

Complete Code

MCU side — Arduino IDE sketch (board "Arduino Leonardo", MCU port):

// Pont série : envoie une trame horodatée vers le SoC x86.
const uint8_t LED = 13;
unsigned long last = 0;
bool on = false;

void setup {
  pinMode(LED, OUTPUT);
  Serial.begin(9600);            // USB série interne vers le CPU hôte
}

void loop {
  if (millis - last >= 1000) {
    last = millis;
    on = !on;
    digitalWrite(LED, on ? HIGH : LOW);
    // Trame simple : LED=<etat>;T=<millis>
    Serial.print("LED=");
    Serial.print(on ? 1 : 0);
    Serial.print(";T=");
    Serial.println(millis);
  }
}

SoC side — pont_serie.py (Linux: /dev/ttyACM0):

import serial

port = serial.Serial("/dev/ttyACM0", 9600, timeout=1)
print("Écoute du MCU... (Ctrl+C pour quitter)")
try:
    for ligne in port:
        texte = ligne.decode("utf-8", errors="replace").strip
        if not texte:
            continue
        champs = dict(p.split("=") for p in texte.split(";"))
        etat = "ALLUMÉE" if champs.get("LED") == "1" else "éteinte"
        print(f"MCU: LED {etat} depuis {champs.get('T')} ms")
finally:
    port.close

Expected Verification

The SoC terminal displays "MCU: LED ON for … ms" every second, alternating, synchronized with the D13 LED. Both halves of the board communicate without any external cable.

Common Errors

• Conflict with pinpong: If Firmata is uploaded to the MCU, it takes over the port; re-upload your sketch to regain control.
• Wrong Arduino IDE board: Select "Arduino Leonardo", not "Uno" — the embedded ATmega32U4 is the component found in the Leonardo.
• Missed bootloader: Press the board's Arduino reset button just after uploading to re-enter the bootloader.
• Port already open: Close the Arduino IDE serial monitor before launching pyserial, otherwise the port is occupied or you get a PermissionError.
• Linux access rights: Run sudo usermod -aG dialout $USER then log out and back in, otherwise access to /dev/ttyACM0 is denied.
• Truncated frames: Read line by line (port iterator) rather than raw read, and always end with println on the MCU side.