stm32u5 HAL_FDCAN_AddMessageToTxFifoQ is always full after error

[lll]

Hello

I have a code use CAN on a stm32U585 he work fine if the CAN bus have not disturbance

But if i have to many disturbance for exemple if i make a short circuit bethen CANH and CANL when i remove the short circuit the CAN no restart to send data. I need stop and restart CAN  

HAL_FDCAN_Stop(&hfdcan1);
HAL_FDCAN_Start(&hfdcan1);

After the disturbance, the return value of HAL_FDCAN_GetState() and HAL_FDCAN_GetError() remains unchanged.

How can I immediately know when there is a problem with CAN

[lll]

correction: HAL_FDCAN_GetTxFifoFreeLevel is always full after error 

[mƎALLEm · Accepted solution]

Hello,

---

@lll wrote:

if i make a short circuit bethen CANH and CANL when i remove the short circuit the CAN no restart to send data.

---

That's normal. The node is in Bus-off state and there is no automatic Bus-off recovery by hardware with FDCAN. You need to do it by software.

To implement the Bus-Off recovery by software you need to:

1. Enable the FDCAN NVIC interrupt line, either manually or using the STM32CubeMX interface.
2. Activate the Bus-Off notification interrupt with the following code: 

   HAL_FDCAN_ActivateNotification(&hfdcan1, FDCAN_IT_BUS_OFF, 0);​

3. implement the error status callback to handle the Bus-Off event:

   void HAL_FDCAN_ErrorStatusCallback(FDCAN_HandleTypeDef *hfdcan, uint32_t ErrorStatusITs)
   {
       FDCAN_ProtocolStatusTypeDef protocol_status;
       HAL_FDCAN_GetProtocolStatus(hfdcan, &protocol_status);
   
       if (protocol_status.BusOff != 0)  // If Bus-Off error occurred
       {
           CLEAR_BIT(hfdcan->Instance->CCCR, FDCAN_CCCR_INIT);  // Clear INIT bit to recover from Bus-Off
       }
   }
   ​

Hope that answers your question.