TMS320F2812: CAN Transmission Acknowledge register (CANTA)

Marcio Borges

Expert 1950 points

Part Number: TMS320F2812

I´d like to know whether the Transmission Acknowledge register (CANTA) must be cleared by the CPU before starting a new transmission or not.

My software does not use interrupts and performs the piece of code bellow before starting a new transmission on mailbox 0.

ECanaShadow.CANTA.all = ECanaRegs.CANTA.all;
ECanaShadow.CANTA.all |= 1;
ECanaRegs.CANTA.all = ECanaShadow.CANTA.all;
do
{
ECanaShadow.CANTA.all = ECanaRegs.CANTA.all;
} while ((ECanaShadow.CANTA.all & 1) == 0);

I ran a test and the software got trapped in the "while loop". In this test there were other nodes on the CAN bus, but no one was operational (acknowledging the message).

Thanks

over 4 years ago

0 Hareesh Janakiraman over 4 years ago

TI__Guru* 95315 points

If you are not using interrupts, you would be polling. In this case, you would want to ensure that the previous transmission is complete before initiating the next transmission. For this reason, you should clear the TA bit when it is set. Otherwise, how would you ensure that the previous transmission was completed successfully.

0 Marcio Borges over 4 years ago in reply to Hareesh Janakiraman

Expert 1950 points

Thank you for the response.

I understand that if the software reads TA it will know that previous transmission was not completed successfully.

But what about the "while loop"? Why the software does not leave it? Is it because eCAN keeps repeating the transmission?

Thanks,

+1 Hareesh Janakiraman over 4 years ago in reply to Marcio Borges

TI__Guru* 95315 points

Marcio Borges said:
But what about the "while loop"? Why the software does not leave it? Is it because eCAN keeps repeating the transmission?

eCAN will keep repeating the transmission until at least one node on the network has sent an ACK. When that happens (and only after that happens), the TA bit of the transmitting mailbox will be set. I have explained this in www.ti.com/lit/SPRA876.

+1 Hareesh Janakiraman over 4 years ago in reply to Hareesh Janakiraman

TI__Guru* 95315 points

In CAN, transmission is not considered successful unless the reception is successful. Reception is considered successful when at least one node received the transmitted frame without any errors and transmitted the ACK bit to the transmitter. Hope this clarifies.

+1 Marcio Borges over 4 years ago in reply to Hareesh Janakiraman

Expert 1950 points

Ok. Thanks for you answrer.

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TMS320F2812: CAN Transmission Acknowledge register (CANTA)