Understand bxCAN TX mailbox

[Ash1]

Hi all

I want to understand behavior of TX mailbox here I am trying to send three ID but only i able to see two ID at a time in TI0R. I have fewer doubts which I hope you can clear.

Doubt 1:  Do I have to use three different mail box for three ID or One is enough .

Doubt 2. Like in RX mailbox I have locking mechanism in which I can see different RX frame in RXFIFO0 so I mean to say It can hold upto three different messages. So is there any logic in TX mailbox also to locked or to see all ID because I think it is overwriting the buffer.

CAN_TxHeaderTypeDef txHeader;
uint8_t tx_data[8] = {0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 0x88};
uint32_t tx_mailbox_used;

txHeader.StdId = 0x3e8; // Example CAN ID
txHeader.RTR = CAN_RTR_DATA;
txHeader.IDE = CAN_ID_STD;
txHeader.DLC = 8;

if (HAL_CAN_AddTxMessage(&hcan1, &txHeader, tx_data, &tx_mailbox_used) != HAL_OK)
{
  Error_Handler();
}

txHeader.StdId = 0x2bc; // Example CAN ID
txHeader.RTR = CAN_RTR_DATA;
txHeader.IDE = CAN_ID_STD;
txHeader.DLC = 8;

if (HAL_CAN_AddTxMessage(&hcan1, &txHeader, tx_data, &tx_mailbox_used) != HAL_OK)
{
  Error_Handler();
}

txHeader.StdId = 0x100; // Example CAN ID
txHeader.RTR = CAN_RTR_DATA;
txHeader.IDE = CAN_ID_STD;
txHeader.DLC = 8;

if (HAL_CAN_AddTxMessage(&hcan1, &txHeader, tx_data, &tx_mailbox_used) != HAL_OK)
{
  Error_Handler();
}

HAL_Delay(1000);
}

B.R

Ashish

[SofLit]

Hello,

First, please see How to insert source code , I've edited your post.

Second, not sure what the problem is, but when sending a CAN frame you need to select an empty mailbox (it's already managed in the HAL).

Please review the reference manual:

See also the HAL implementation of HAL_CAN_AddTxMessage():

    /* Check that all the Tx mailboxes are not full */
    if (((tsr & CAN_TSR_TME0) != 0U) ||
        ((tsr & CAN_TSR_TME1) != 0U) ||
        ((tsr & CAN_TSR_TME2) != 0U))
    {
      /* Select an empty transmit mailbox */
      transmitmailbox = (tsr & CAN_TSR_CODE) >> CAN_TSR_CODE_Pos;

      /* Store the Tx mailbox */
      *pTxMailbox = (uint32_t)1 << transmitmailbox;

PS: could you please state on this thread please?