Now I want to check if the 2 CAN buses work.

I am going to use the stm32f407.ino example from this repository : https://github.com/nopnop2002/Arduino-STM32-CAN

1/In the stm32f407.ino I add these lines (in the

"bool CANInit(BITRATE bitrate, int remap)" function) in order to match to the hardware :

  if (remap == 4) {
    // CAN1
    RCC->AHB1ENR |= 0x2;                 // Enable GPIOB clock 
    CANSetGpio(GPIOB, 8);                // Set PB8
    CANSetGpio(GPIOB, 9);                // Set PB9
    
    // CAN2
    RCC->AHB1ENR |= 0x2;                 // Enable GPIOB clock 
    CANSetGpio(GPIOB, 5);                // Set PB5
    CANSetGpio(GPIOB, 6);                // Set PB6
  }

2/In the setup add :

    bool ret = CANInit(CAN_1000KBPS, 4);

If you want to send to CAN2:

  //uint8_t send_ch = 1; //send to CAN1
  uint8_t send_ch = 2; ////send to CAN2

Both CAN work : we have the bases !