#include <M5Core2.h>
#include <Wire.h>
#define I2C_DEV_ADDR 0x55
uint32_t i = 0;

void setup() {

M5.begin(true, true, true, true);
delay(300);

Serial.setDebugOutput(true);
Wire.begin(32,33);  // SDA SCL M5Stack Core 2

}

void loop() {
delay(5000);

//Write message to the slave
Wire.beginTransmission(I2C_DEV_ADDR);
Wire.printf("Hello World! %u", i++);
uint8_t error = Wire.endTransmission(true);
Serial.printf("endTransmission: %u\n", error);

//Read 16 bytes from the slave
error = Wire.requestFrom(I2C_DEV_ADDR, 16);
Serial.printf("requestFrom: %u\n", error);
if(error){
uint8_t temp[error];
Wire.readBytes(temp, error);
log_print_buf(temp, error);
}

}

M5Atom Matrix code here:

//#include "M5Atom.h"
#include "M5StickC.h"
#include <Wire.h>
#define I2C_DEV_ADDR 0x55

uint32_t i = 0;

void onRequest(){
Wire.print(i++);
Wire.print(" Packets.");
Serial.println("onRequest");
}

void onReceive(int len){
Serial.printf("onReceive[%d]: ", len);
while(Wire.available()){
Serial.write(Wire.read());
}
Serial.println();
}

void setup() {

M5.begin(true,true,true);
delay(300);

Serial.begin(115200);
Serial.setDebugOutput(true);
Wire.onReceive(onReceive);
Wire.onRequest(onRequest);
Wire.begin(26,32); // SDA SCL M5Atom

}

void loop() {

}