RTOS: F28M36x: CAN status after CANMessageSet - shows still TX'ing even though data was sent

Steve Goodrich

Tool/software: TI-RTOS

I have a project using two F28M36x parts on separate PCBs, connected via CAN bus. My CAN::Send() method boils down to this:

    CANMessageSet(CAN0_BASE, 32, &msgObject, MSG_OBJ_TYPE_TX);
    status = CANStatusGet(CAN0_BASE, CAN_STS_TXREQUEST);
    long ulTimer = 2500 * CAN_SEND_TIMEOUT_MS;
    timeout = false;
    while (status != 0) {
        if (--ulTimer < 0) {
            timeout = true;
            break;
        }
        status = CANStatusGet(CAN0_BASE, CAN_STS_TXREQUEST);
    }

If 'timeout' is true, this code will be re-executed.

The problem is that CANStatusGet() is sometimes returning 0x80000000, which I believe indicates that the transmit has not yet completed. Since I need to guarantee delivery, the code re-sends the message. The odd part is that the data is actually sent, regardless of the value returned by CANStatusGet().

Am I using the CANStatusGet() API call correctly? Is there a different way to determine that the data was actually sent?

Hmm... is there some errata that I've missed regarding either the CAN API or the F28M36x CAN controller?

Thanks!
-- Steve G.

over 8 years ago

0 Christopher Chiarella over 8 years ago

TI__Mastermind 30255 points

Steve,

Yes, the bit being set for message object 32 indicates the transmission of the message object is requested and not yet done. This is the correct way to determine if the message object has transmitted. There is also a TxOK bit in the error and status register that can be read but that doesn't provide information regarding which message object it is referring to.

Best Regards
Chris

0 Steve Goodrich over 8 years ago in reply to Christopher Chiarella

Intellectual 515 points

Chris,
The odd thing is that the status bit is still set, but my interrupt handler has fired and indicates that the message object has been sent. I changed my code to use interrupts (as I've seen in several other posts on these forums) and it works. The status bit still says that the message was not sent, but the interrupt flag indicates that the message was sent and the message is seen at the CAN receiver.

Hmm... could this be a silicon bug?

0 Adam Haun over 8 years ago in reply to Steve Goodrich

TI__Expert 8950 points

Steve,

It's doubtful that this is a silicon bug. This CAN module has been in the field for many years now.

Are you transmitting in a loop? It is possible that you're starting a new transmission right as the old one is finishing?

0 Steve Goodrich over 8 years ago in reply to Adam Haun

Intellectual 515 points

We are transmitting in a loop. The code transmits a messages, waits for the bit to be clear in the status register (indicating that the message was sent), then sends the next message. The problem is that the message is sent but the status bit doesn't clear (or appears not to clear).

0 Adam Haun over 8 years ago in reply to Steve Goodrich

TI__Expert 8950 points

Is only one message sent, or are you able to transmit continuously?

We'll look into the timing of the status bits and interrupt.

0 Steve Goodrich over 8 years ago in reply to Adam Haun

Intellectual 515 points

Every 250 ms or so I check to see if the message was sent. If not sent, I decrease a count. When the count reaches zero, I resend.

Messages continue to be sent on every retry, even though the status bit says the message has not been sent.

0 Adam Haun over 8 years ago in reply to Steve Goodrich

TI__Expert 8950 points

Steve,

The interrupt is indeed triggered before the TXRQ bit is cleared. I will put in a ticket to update the documentation with clearer timings for the interrupts and status bits.

Sorry for the confusion,

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RTOS: F28M36x: CAN status after CANMessageSet - shows still TX'ing even though data was sent