CAN Transmit Loopback Mode

[MZimm.3]

Hello all,

I would like to put the CAN2 interface into operation on a NUCLEO STM32F466RE board. For this purpose I have programmed an example in which a BYTE array HELLO is to be sent in the loopback.

If I now pass the TxHeader Struct to the HAL_CAN_AddTxMessage() method, this method is executed without error. The signal recording on the TX pin also shows a data transmission. It's just not the data I expected.

My data from the TxHeader cannot be entered in the mailbox register. It looks like the registers are locked, although all mailboxes report that they are free.

What else can I do wrong at this point?

What else could be the reason that the mailbox cannot be written to?

Greetings

Michael

[Karl Yamashita]

Post relevant code so we can see any possible issue

[Javier1]

>>What else could be the reason that the mailbox cannot be written to?

the mailbox could be already full, is your code checking before trying to send?

[MZimm.3]

This is my CAN Init method. I actually took everything from an example on the internet. 

void main_CAN2Init(void)

{

hcan2.Instance = CAN2;

hcan2.Init.Mode = CAN_MODE_LOOPBACK; // Zum testen im Loopback mode

hcan2.Init.AutoBusOff = DISABLE;

hcan2.Init.AutoRetransmission = ENABLE;

hcan2.Init.AutoWakeUp = DISABLE;

hcan2.Init.ReceiveFifoLocked = DISABLE;

hcan2.Init.TimeTriggeredMode = DISABLE;

hcan2.Init.TransmitFifoPriority = DISABLE;

// Settings related to CAN bit Timing

hcan2.Init.Prescaler = 2;

hcan2.Init.SyncJumpWidth = CAN_SJW_1TQ;

hcan2.Init.TimeSeg1 = CAN_BS1_6TQ;

hcan2.Init.TimeSeg2 = CAN_BS2_1TQ;

if(HAL_CAN_Init(&hcan2) != HAL_OK)

{

Error_Handler("Error main_CAN2Init\n");

}

}

And this is the send method

static void CAN2_Tx(void)

{

CAN_TxHeaderTypeDef TxHeader;

uint32_t TxMailbox;

uint8_t new_message[] = {'H','E','L','L','O'};

TxHeader.DLC = 5;

TxHeader.StdId = 0x65D;

TxHeader.ExtId = 0;

TxHeader.IDE = CAN_ID_STD;

TxHeader.RTR = CAN_RTR_DATA;

TxHeader.TransmitGlobalTime = DISABLE;

if(HAL_CAN_AddTxMessage(&hcan2, &TxHeader, new_message, &TxMailbox) != HAL_OK)

{

Error_Handler("Error in Methode CAN2_Tx\n");

}

while(HAL_CAN_IsTxMessagePending(&hcan2, TxMailbox));

sprintf(uartText,"CAN Message Transmitted\n");

uart2Transmit(0, (uint8_t*)uartText, strlen(uartText));

}

And the Transmit Mailbox Bits indicate that there is no transmit request pending

 

[Javier1]

try this

	howmanyTXmailboxes = HAL_CAN_GetTxMailboxesFreeLevel(hcan_object_reference);
	if (howmanyTXmailboxes > 0) {
		status = HAL_CAN_AddTxMessage(hcan_object_reference, &canTxheader,
				messageTxData, &pTxMailbox);
		if (status != HAL_OK) {
			//Error_handler(); error de transmision
		}
	}else{
		status=HAL_BUSY;
	}
	return status;

[MZimm.3]

Thanks for the idea

When I look at the answer in the debugger, all three mailboxes are free.

Name : howmanyTXmailboxes

Details:3

Default:3

Decimal:3

Hex:0x3

Binary:11

Octal:03

[Javier1]

what about removing that Loopback and properly wiring the canbus somewhere

[MZimm.3]

I have also tried it with a CAN bus and a CAN analyser. Unfortunately with the same result.

Now I have done the whole CAN initialisation on CAN1. On CAN1 my test software runs immediately. I can see in the debugger how the mailboxes are written with my data and the data I expect is transmitted.

Now I am asking myself why it works on CAN1 and not on CAN2.

[SofLit · Accepted solution]

Hello,

Try to enable also RCC CAN1 clock even using CAN2 only and see what happen.

[MZimm.3]

Hello all,

that was the important tip. Now it works on both CAN interfaces. Document RM0390 also says that CAN2 is only a slave and has no direct access to the SRAM. That was probably the reason why I could not write to the mailboxes.

Many thanks to all for your time and effort. 

Greetings Michael