CAN node goes silent for good

The code

Embedded C for Cortex-M. It compiles. There are 3 real bugs in it: the kind that pass a bench test and fail in the field.

void MX_CAN1_Init(void)
{
    hcan1.Instance = CAN1;
    hcan1.Init.Prescaler = 5;
    hcan1.Init.Mode = CAN_MODE_NORMAL;
    hcan1.Init.SyncJumpWidth = CAN_SJW_1TQ;
    hcan1.Init.TimeSeg1 = CAN_BS1_13TQ;
    hcan1.Init.TimeSeg2 = CAN_BS2_2TQ;
    hcan1.Init.AutoBusOff = DISABLE;
    hcan1.Init.AutoRetransmission = ENABLE;
    HAL_CAN_Init(&hcan1);
    HAL_CAN_Start(&hcan1);
}

bool can_send_status(const uint8_t d[8])
{
    CAN_TxHeaderTypeDef h = { .StdId = 0x321, .IDE = CAN_ID_STD, .RTR = CAN_RTR_DATA, .DLC = 8 };
    uint32_t mb;
    while (HAL_CAN_GetTxMailboxesFreeLevel(&hcan1) == 0) { }
    HAL_CAN_AddTxMessage(&hcan1, &h, d, &mb);
    return true;
}

What an interviewer expects

• Point to each line you'd stop in a code review.
• Say what actually breaks: the failure mode, not just the rule it violates.
• Fix it, then defend the fix when asked the follow-up.

The bugs, reference fixes and the follow-up question are in the practice app, after you've tried it.

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