TMS320F280049: Report Bit0 Error

Hi Cherry,

First of all, when CAN communication is used we strongly discourage customers to use the internal oscillators as the main clock source as the accuracy of the internal oscillator may not be able to meet the clocking requirements of CAN.  This has been emphasized in the TRM as a note and maybe point this out to the customer.

As for the bit0 error and bus off condition these conditions should not happen in loopback mode.  For the customer's code, can you please check if they have retained the below statement:

          CAN_enableTestMode(CANA_BASE, CAN_TEST_EXL);

A bit0 error and a bus-off condition occurring at the instant the ISR is serviced is an indication that CAN is probably not in loopback mode.  A bit 0 error occurs when CAN needs to transmit a dominant '0' state but the bus is monitoring a recessive '1' state so somehow, it looks like external CAN connections are still involved in the code.  When enough errors occur (maybe a series of bit 0 errors happening due to unsuccessful re transmission attempts), the CAN module would isolate the bus by putting in in bus off state.  Again, these are indications that test is probably not in loopback mode.

Regards,

Joseph

Hi Joseph,

Thanks for your help.

They've tried 50K baud rate, and remain the same error.

The program has called CAN_disableTestModule(CANA_BASE) before calling CAN_startModule(CANA_BASE) (that is, before entering normal operating mode).

Joseph Casuga said:

CAN_enableTestMode(CANA_BASE, CAN_TEST_EXL);

No, they didn't retain this statement, which can also be seen from the register value CAN_CTL.TEST=0.

Yes, the Tx waveform in loopback mode is normal and there is no bit0 error, the ISR error interrupt is entered in normal mode.

The Tx waveform in the screenshot is not high for approximately 135 us after the first falling edge occurs (approximately 16 to 17 bittimes), so a bit0 error is reported.

Why does this waveform occur as soon as it enters normal mode? In theory, the loopback mode test is OK, and this should also be transmitted properly because the TX is floating.

Thanks and regards,

Cherry

And the following is the code that has been removed from loopback mode. The problem is still as the same.

    // Initialize GPIO and configure GPIO pins for CANTX/CANRX on module A
    GPIO_setPinConfig(DEVICE_GPIO_CFG_CANRXA);
    GPIO_setPinConfig(DEVICE_GPIO_CFG_CANTXA);
    GPIO_setMasterCore(DEVICE_GPIO_PIN_CANRXA, GPIO_CORE_CPU1);
    GPIO_setMasterCore(DEVICE_GPIO_PIN_CANTXA, GPIO_CORE_CPU1);
    GPIO_setPadConfig(DEVICE_GPIO_PIN_CANRXA, GPIO_PIN_TYPE_PULLUP /*GPIO_PIN_TYPE_STD*/);  // for Rx pin is uncornnect.
    GPIO_setQualificationMode(DEVICE_GPIO_PIN_CANRXA, GPIO_QUAL_ASYNC);
    GPIO_setQualificationMode(DEVICE_GPIO_PIN_CANTXA, GPIO_QUAL_ASYNC);

    CAN_initModule(CANA_BASE);// Initialize the CAN controllers

    CAN_setBitRate(CANA_BASE, DEVICE_SYSCLK_FREQ, 50000, 20);// Set up the CAN bus bit rate to 50kHz.  CAN_Clock = 80M.  bitTime = 20(Tq)

    CAN_enableInterrupt(CANA_BASE, (CAN_INT_IE0 | CAN_INT_ERROR | CAN_INT_STATUS));// Enable interrupts on the CAN A peripheral.

    Interrupt_register(INT_CANA0, &CanAISR);// This registers the interrupt handler in PIE vector table.

    // Enable the CAN-A interrupt signal
    Interrupt_enable(INT_CANA0);
    CAN_enableGlobalInterrupt(CANA_BASE, CAN_GLOBAL_INT_CANINT0);
    
    CAN_clearInterruptStatus(CANA_BASE, 31);
    CAN_getStatus(CANA_BASE);
    CAN_setupMessageObject(CANA_BASE, 31, 0x0000, CAN_MSG_FRAME_STD, CAN_MSG_OBJ_TYPE_TX, 0, CAN_MSG_OBJ_NO_FLAGS, 0);
    CAN_clearGlobalInterruptStatus(CANA_BASE, CAN_GLOBAL_INT_CANINT0);
    
    CAN_startModule(CANA_BASE);// Start CAN module A operations
    
    uint16_t senddata[8] = {0};
    CAN_sendMessage(CANA_BASE, 31, 0, senddata);