TM4C123G CAN TX update data bytes only

Yes, I know CANMessageSet will send a message. It also configures the message object completely and it is a blocking function (while not busy loop inside).

I do not need the overhead of setting the complete message. I want to configure the message object once and have a short quick function to update the data bytes when needed and transmit the message with its current settings, as described in datasheet "17.3.5 Updating a Transmit Message Object".

Mariano

One of the problems I found:

I send two messages back to back using TIVA's CANMessageSet with AutoRetry set to off:

tCANMsgObject msgobject;

CANRetrySet(CAN0_BASE, false);

can.txdata = data;
can.ptxdata = (uint8_t *) (&can.txdata);
msgobject.pui8MsgData = can.ptxdata;
msgobject.ui32MsgIDMask= 0;
msgobject.ui32Flags = 0;
msgobject.ui32MsgLen = 4;
msgobject.ui32MsgID = 1365;
CANMessageSet(CAN0_BASE, 1, &msgobject, MSG_OBJ_TYPE_TX);
msgobject.ui32MsgID = 10;
CANMessageSet(CAN0_BASE, 2, &msgobject, MSG_OBJ_TYPE_TX);

Half of the time only one message goes through, the rest of the time both go out. When only ONE goes out, I get no error flag, no error count and no TX pending bit (checking CAN_STS_CONTROL, CAN_STS_TXREQUEST and CANErrCntrGet). So why is the micro not sending the second object? and why is it not flagging an error? Am I missing something here?

Mariano

The example in Tivaware uses interrupts, I am not using interrupts. I have tested both BUSY flag and TXOK flag through CANStatusGet to send two messages back to back, still lose a message and get no error back. I have tested CANTXRQ1 and still lose messages. What other flag am I missing?

	tCANMsgObject msgobject;

	CANRetrySet(CAN0_BASE, false);
	can.txdata = data;
	can.ptxdata = (uint8_t *) (&can.txdata);
	msgobject.pui8MsgData = can.ptxdata;
	msgobject.ui32MsgIDMask= 0;
	msgobject.ui32Flags = 0;
	msgobject.ui32MsgLen = 4;

	while ((CANStatusGet(CAN0_BASE, CAN_STS_CONTROL)&CAN_STS_TXOK)!=0);
	msgobject.ui32MsgID = 1365;
	CANMessageSet(CAN0_BASE, 1, &msgobject, MSG_OBJ_TYPE_TX);

	while ((CANStatusGet(CAN0_BASE, CAN_STS_CONTROL)&CAN_STS_TXOK)!=0);
	msgobject.ui32MsgID = 10;
	CANMessageSet(CAN0_BASE, 2, &msgobject, MSG_OBJ_TYPE_TX);

Amit, your response seems to have fixed the problem. In TIVA's library can.c CANStatusGet() function, the following is executed:

        case CAN_STS_CONTROL:
        {
            ui32Status = HWREG(ui32Base + CAN_O_STS);
            HWREG(ui32Base + CAN_O_STS) = ~(CAN_STS_RXOK | CAN_STS_TXOK |
                                            CAN_STS_LEC_M);
            break;
        }

The register is read and cleared after it is read, regardless whether the flags where set or not when first read. I believe this created a race condition where it is possible that the TXOK bit is set between the read process and the clear process. As soon as I modified this function to avoid the race condition, I was unable to replicate the problem.

I am going to rewrite my software to use register access directly and void using the TIVA library, hopefully I will get everything to work. You can close this thread. Thanks for your help!