I understand in using this library you can successfully transmit data using port B but not port A, correct? That should mean the library itself works ok.

What speed are you trying to use? I successfully tested with 125kBits and 500kBits.

Thanks
Felix

Maybe there is more I need to do so it doesn't attempt to do any SPI on that port?

the code compiled for me after disabling the SPI chips using CAN1. I also removed all mcp* files from the libray's src directory. And yes, I successfully tested sending messages back and forth using either port.

Which CAN library are you using?

Thanks
Felix

I did a test with the 2 relay board on Port A, GPIO 15 and 13 and it does work just fine...

hmm, both M5Dial ports (A and B) work for me. I used this CAN example as basis. Below is the beginning of setup():

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

  Serial.println("Initializing ...");

  CAN0.setCANPins(GPIO_NUM_15, GPIO_NUM_13); // Port A - works
//  CAN0.setCANPins(GPIO_NUM_1, GPIO_NUM_2); // Port B - works
  CAN0.begin(500000);

  Serial.println("Ready ...!");

Thanks
Felix

CAN0.setCANPins(GPIO_NUM_1, GPIO_NUM_2);

It is just a StampS3 inside and I just wrote a sketch and confirmed that pin15 will turn on an LED when the button '0' is pushed.
The ESP32 uses an IOMUX to allow almost any pin to have any function.
Hope this helps, -Terry

and the pins are labeled as being for I2C, so just thinking that there is other circuitry that is blocking RX /TX operation or other software configured to force them in another mode?