https://github.com/aaknitt/esp32_can/tree/master

Put this code in lib and change the pin designations in esp32_can.cpp:
ESP32CAN attribute((weak)) CAN0(GPIO_NUM_1, GPIO_NUM_2) ;

platformio.ini looks like this:

[env:m5stack-stamps3]
platform = espressif32
board = m5stack-stamps3
framework = arduino

lib_deps =
https://github.com/collin80/can_common
https://github.com/plapointe6/EspMQTTClient
m5stack/M5Dial
m5stack/M5Unified

upload_speed = 1500000
monitor_speed = 115200

Plug it into Port B

Setup code is like:
CAN0.setCANPins(GPIO_NUM_1, GPIO_NUM_2);
USBSerial.println("Set CAN pins...");
CAN0.begin(500000);
USBSerial.println("CAN has started...");
CAN0.watchFor();
CAN0.setCallback(0, theCanDecoder);

If you want full code I can probably clean this all up and publish on Git.

these GPIOs look ok to me. Hmm, not sure why it doesn't work on M5Core2 though. Sorry.

Thanks
Felix

and I'm able to see activity on the CAN bus using an oscilloscope.

I assume you've adapted the TX and RX GPIOs for M5Core2 accordingly, yes?

Thanks
Felix

#include "M5Atom.h"
#include <ESP32CAN.h>
#include <CAN_config.h>

#define CAN_BASE // Remove to use external CAN bus via Grove cable
//#define CAN_RECIEVER // Remove to make sender

#define CAN_MSG_ID 0x001

CAN_device_t CAN_cfg; // CAN Config.
unsigned long previousMillis = 0; // will store last time a CAN Message was sent // send. 将存储上次发送CAN消息的时间。
const int interval = 80; // interval at which send CAN Messages (milliseconds).

const int rx_queue_size = 10; // Receive Queue size.
int LedNumberCount = 0;
int waitCANData = 0;

uint8_t msgcnt = 0;

void setup()
{
M5.begin(true, true, true);
Serial.println("Atom Install OK....");
M5.dis.fillpix(CRGB(100, 0, 0)); //Fill the LED Matrix RED
delay(2000);

#ifdef CAN_BASE // CAN base is used
//default
CAN_cfg.tx_pin_id = GPIO_NUM_22;
CAN_cfg.rx_pin_id = GPIO_NUM_19;

#else
// Grove
CAN_cfg.tx_pin_id = GPIO_NUM_26;
CAN_cfg.rx_pin_id = GPIO_NUM_32;
#endif

CAN_cfg.speed = CAN_SPEED_500KBPS;

CAN_cfg.rx_queue  = xQueueCreate(rx_queue_size, sizeof(CAN_frame_t));

ESP32Can.CANInit();
Serial.println("CAN Install");
M5.dis.fillpix(CRGB(0, 100, 0));  //Fill the LED Matrix GREEN

M5.dis.fillpix(CRGB(HUE_GREEN)); //Fill the LED Matrix GREEN
#ifdef CAN_RECIEVER
Serial.println("Set as RECIEVER");
#else
Serial.println("Set as SENDER");
#endif
}

void loop()
{
unsigned long currentMillis = millis();

#ifdef CAN_RECIEVER
// recieve CAN Message
CAN_frame_t rx_frame;

if (xQueueReceive(CAN_cfg.rx_queue, &rx_frame, 3 * portTICK_PERIOD_MS) ==  pdTRUE) 
{
    if (rx_frame.FIR.B.FF == CAN_frame_std) 
    {
        Serial.printf("New standard frame");
    } 
    else
    {
        Serial.printf("New extended frame");
    }

    if (rx_frame.FIR.B.RTR == CAN_RTR) 
    {
        Serial.printf(" RTR from 0x%08X, DLC %d\r\n", rx_frame.MsgID, rx_frame.FIR.B.DLC);
    }
    else
    {
        Serial.printf(" from 0x%08X, DLC %d, Data ", rx_frame.MsgID, rx_frame.FIR.B.DLC);
        for (int i = 0; i < rx_frame.FIR.B.DLC; i++) 
        {
            Serial.printf("0x%02X ", rx_frame.data.u8[i]);
        }
        Serial.printf("\n");
        if (rx_frame.data.u8[0] == 0x01) 
        {
            CAN_frame_t tx_frame;
            tx_frame.FIR.B.FF   = CAN_frame_std;
            tx_frame.MsgID      = CAN_MSG_ID;
            tx_frame.FIR.B.DLC  = 8;
            tx_frame.data.u8[0] = 0x02;
            tx_frame.data.u8[1] = rx_frame.data.u8[1];
            tx_frame.data.u8[2] = 0x00;
            tx_frame.data.u8[3] = 0x00;
            tx_frame.data.u8[4] = 0x00;
            tx_frame.data.u8[5] = 0x00;
            tx_frame.data.u8[6] = 0x00;
            tx_frame.data.u8[7] = 0x00;
            ESP32Can.CANWriteFrame(&tx_frame);
        }
    }
}

#else
// Send CAN Message
if (currentMillis - previousMillis >= interval)
{
// ESP32Can.CANInit();
previousMillis = currentMillis;
CAN_frame_t tx_frame;
tx_frame.FIR.B.FF = CAN_frame_std;
tx_frame.MsgID = CAN_MSG_ID;
tx_frame.FIR.B.DLC = 8;
tx_frame.data.u8[0] = 0x01;
tx_frame.data.u8[1] = msgcnt;
tx_frame.data.u8[2] = 0x00;
tx_frame.data.u8[3] = 0x00;
tx_frame.data.u8[4] = 0x00;
tx_frame.data.u8[5] = 0x00;
tx_frame.data.u8[6] = 0x00;
tx_frame.data.u8[7] = 0x00;

    ESP32Can.CANWriteFrame(&tx_frame);
    // ESP32Can.CANStop();
    msgcnt++;
    if (msgcnt > 29) 
    {
        msgcnt = 0;
    }
}

CAN_frame_t rx_frame;

if (xQueueReceive(CAN_cfg.rx_queue, &rx_frame, 3 * portTICK_PERIOD_MS) == pdTRUE) 
{
    if (rx_frame.FIR.B.FF == CAN_frame_std) 
    {
        Serial.printf("New standard frame");
    } 
    else 
    {
        Serial.printf("New extended frame");
    }

    if (rx_frame.FIR.B.RTR == CAN_RTR) 
    {
        Serial.printf(" RTR from 0x%08X, DLC %d\r\n", rx_frame.MsgID,
        rx_frame.FIR.B.DLC);
    } 
    else 
    {
        Serial.printf(" from 0x%08X, DLC %d, Data ", rx_frame.MsgID,
        rx_frame.FIR.B.DLC);
        for (int i = 0; i < rx_frame.FIR.B.DLC; i++) 
        {
            Serial.printf("0x%02X ", rx_frame.data.u8[i]);
        }
        Serial.printf("\n");

        if (rx_frame.data.u8[0] == 0x02) 
        {
                if (rx_frame.data.u8[1] < 25)
            {
                M5.dis.drawpix(rx_frame.data.u8[1], CRGB(100, 0, 0));
            } 
            else if (rx_frame.data.u8[1] > 27) 
            {
                M5.dis.fillpix(CRGB(0, 0, 20));
            }
            waitCANData = 0;
        }
    }
}

#endif
// waitCANData
M5.update();
if (M5.Btn.isPressed())
{
M5.dis.clear();
M5.dis.fillpix(CRGB(0, 100, 0));
esp_restart();
}
delay(10);
}

when I modify it to work with the Core2, it compiles OK but no echo back. what am I missing?

; PlatformIO Project Configuration File
;
; Build options: build flags, source filter
; Upload options: custom upload port, speed and extra flags
; Library options: dependencies, extra library storages
; Advanced options: extra scripting
;
; Please visit documentation for the other options and examples
; https://docs.platformio.org/page/projectconf.html

[env:m5stack-stamps3]
platform = espressif32
board = m5stack-stamps3
framework = arduino
lib_deps =
m5stack/M5Dial@^1.0.2
m5stack/M5Unified@^0.1.11
m5stack/M5GFX@^0.1.11
platform_packages = framework-arduinoespressif32@https://github.com/espressif/arduino-esp32/archive/refs/tags/2.0.14.zip
upload_speed = 1500000
monitor_speed = 115200

Start of code:

/**

• @file encoder.ino
• @author SeanKwok (shaoxiang@m5stack.com)
• @brief M5Dial Encoder Test
• @version 0.2
• @date 2023-10-18
• @Hardwares: M5Dial
• @Platform Version: Arduino M5Stack Board Manager v2.0.7
• @Dependent Library:
• M5GFX: https://github.com/m5stack/M5GFX
• M5Unified: https://github.com/m5stack/M5Unified
  */

#include "M5Dial.h"

void setup()
{
auto cfg = M5.config();
M5Dial.begin(cfg, true, false);
......
.....
.....
etc

and for the M5 Core2
Platformio.ini =
; PlatformIO Project Configuration File
;
; Build options: build flags, source filter
; Upload options: custom upload port, speed and extra flags
; Library options: dependencies, extra library storages
; Advanced options: extra scripting
;
; Please visit documentation for the other options and examples
; https://docs.platformio.org/page/projectconf.html

[env:m5stack-core2]
platform = espressif32
board = m5stack-core2
framework = arduino
platform_packages =
framework-arduinoespressif32@https://github.com/espressif/arduino-esp32/archive/refs/tags/2.0.14.zip
lib_deps =
m5stack/M5Unified@^0.1.11

upload_speed = 1500000
monitor_speed = 115200

and start of code:

/*

• Minimum code to get a display on the
• M5Stack Core2
• Using PlatformIO and Arduino

*/
#include <Arduino.h>
#include <M5Unified.h>
#include <M5GFX.h>

void setup()
{
M5.begin();
....
etc

and for the M5Stack Core3S

Platformio.ini
; PlatformIO Project Configuration File
;
; Build options: build flags, source filter
; Upload options: custom upload port, speed and extra flags
; Library options: dependencies, extra library storages
; Advanced options: extra scripting
;
; Please visit documentation for the other options and examples
; https://docs.platformio.org/page/projectconf.html

[env:m5stack-cores3]
platform = espressif32
board = m5stack-cores3
framework = arduino
lib_deps =
tinyu-zhao/BMI270_Sensor@^0.0.1
m5stack/M5CoreS3@^0.0.4
m5stack/M5Unified@^0.1.11
platform_packages =
framework-arduinoespressif32@https://github.com/espressif/arduino-esp32/archive/refs/tags/2.0.14.zip

build_flags =
-DESP32S3
-DBOARD_HAS_PSRAM
upload_speed = 1500000
monitor_speed = 115200

and code start
/*

• Copyright (c) 2023 by M5Stack

•              Equipped with M5CoreS3 sample source code
  

• Visit for more information:
• https://docs.m5stack.com/en/core/CoreS3 - Docs
• https://github.com/m5stack/M5CoreS3 - GitHub
• Describe: Hello World
• Date: 2023/5/3

*/

#include <Arduino.h>
#include <M5CoreS3.h>

void setup()
{
M5.begin(true, true, false); // Init M5CoreS3.
...
etc

Yours Simon M

which examples have you tried? Maybe this example code can help?

Thanks
Felix