🛠 Exploiter le double cœur : M7 pour le PLC, M4 en coprocesseur

Objectives

Understand and leverage the dual-core architecture of the Opta's STM32H747XI: Cortex-M7 up to 480 MHz (the PLC sketch) and Cortex-M4 up to 240 MHz (available as a Zephyr coprocessor, documented for the arduino_opta board). Use cases: offload intensive processing from the M7 (FFT filtering, network management, display driving) to the M4, and exchange data via shared memory. This is the "bare metal / RTOS" level of the Opta.

Hardware

• Arduino Opta (any variant)
• Zephyr SDK (west workspace) with the arduino_opta board, m7 and m4 targets
• Probe/debugger or serial port to monitor both cores
• Knowledge of RTOS and shared memory

Complete Code

/* copro_m4.c — firmware Zephyr cote M4 (board arduino_opta@m4)
 * Publie une table de mesures dans la RAM partagee ; le M7 la lit.
 */
#include <zephyr/kernel.h>
#include <zephyr/device.h>

/* Zone partagee conventionnee (adresse a adapter a votre layout memoire) */
struct partage {
  uint32_t seq;        /* numero de sequence, incremente par le M4 */
  int32_t  mesures[8]; /* 8 valeurs d'entrees 0-10 V converties */
};
volatile struct partage *shm = (volatile struct partage *)0x30060000;

void main(void) {
  uint32_t n = 0;
  while (1) {
    for (int i = 0; i < 8; i++) shm->mesures[i] = (int32_t)(n * (i + 1));
    shm->seq = ++n;                 /* ecriture de fin : le M7 teste seq */
    k_msleep(10);
  }
}

// cote_m7.ino — lecture cote sketch Arduino (core mbed_opta)
struct Partage { uint32_t seq; int32_t mesures[8]; };
volatile Partage* shm = (volatile Partage*)0x30060000; // meme zone
void loop {
  uint32_t s = shm->seq;
  Serial.printf("seq=%u m0=%d\n", s, shm->mesures[0]);
  delay(100);
}

Expected Verification

The M4 increments the sequence every 10 ms; the M7 displays increasing sequence numbers and consistent measurements. > one.

Common Errors

• Overwriting the other core's memory zone: without a validated memory layout, the two firmwares can interfere with each other (the Zephyr core loads sketches in LLEXT, already sensitive to the documented "undefined symbol" and OOM issues).
• Race condition: reading seq before the measurements corrupts the read; re-read seq afterwards and discard if changed (seqlock pattern).
• Confusing the cores: the Arduino sketch runs on the M7; the M4 is only usable with a dedicated Zephyr firmware, not from the standard Arduino IDE.
• Wrong compilation target: arduino_opta has distinct m7 and m4 targets; flashing the wrong ELF leaves one core silent.