Tiva C CAN bit Timing error

Do-Myung Kim

Hi, Ti employed.

If the Tiva series still implements the Bosch C_CAN module, I think that there are several error in Tiva C ware CAN driver.

typedef struct
{
    //
    //! This value holds the sum of the Synchronization, Propagation, and Phase
    //! Buffer 1 segments, measured in time quanta. The valid values for this
    //! setting range from 2 to 16.
    //
    uint32_t ui32SyncPropPhase1Seg;

    //
    //! This value holds the Phase Buffer 2 segment in time quanta. The valid
    //! values for this setting range from 1 to 8.
    //
    uint32_t ui32Phase2Seg;

    //
    //! This value holds the Resynchronization Jump Width in time quanta. The
    //! valid values for this setting range from 1 to 4.
    //
    uint32_t ui32SJW;

    //
    //! This value holds the CAN_CLK divider used to determine time quanta.
    //! The valid values for this setting range from 1 to 1023.
    //
    uint32_t ui32QuantumPrescaler;
}
tCANBitClkParms;

The source code CANBitTimingGet() shows psClkParms->ui32SyncPropPhase1Seg = ((ui32BitReg & CAN_BIT_TSEG1_M) >> CAN_BIT_TSEG1_S) + 1;

This means that ui32SyncPropPhase1Seg => CAN_BIT_TSEG1_S = Prop + Phase1Seg, it does't include Sync.

As a result, CANBitTimingSet() function incorrectly set the can bit timing parameter.

For Example,

SystemClock : 80Mhz, BitRate: 500 kbps

CANBitRateSet(CAN0_BASE, 80000000, 500000);

CANBitTimingGet(CAN0_BASE, &g_sCANBitClkParms);

This code set the g_sCANBitClkParms as follows.

g_sCANBitClkParms ->ui32SyncPropPhase1Seg = 8

g_sCANBitClkParms->ui32Phase2Seg = 6

g_sCANBitClkParms->ui32QuantumPrescaler = 9

These are real value( resister value + 1 ).

#define CAN_BIT_VALUE(seg1, seg2, sjw)                                        \
                                ((((seg1 - 1) << CAN_BIT_TSEG1_S) &           \
                                  CAN_BIT_TSEG1_M) |                          \
                                 (((seg2 - 1) << CAN_BIT_TSEG2_S) &           \
                                  CAN_BIT_TSEG2_M) |                          \
                                 (((sjw - 1) << CAN_BIT_SJW_S) &              \
                                  CAN_BIT_SJW_M))

static const uint16_t g_ui16CANBitValues[] =
{
    CAN_BIT_VALUE(2, 1, 1),     // 4 clocks/bit
    CAN_BIT_VALUE(3, 1, 1),     // 5 clocks/bit
    CAN_BIT_VALUE(3, 2, 2),     // 6 clocks/bit
    CAN_BIT_VALUE(4, 2, 2),     // 7 clocks/bit
    CAN_BIT_VALUE(4, 3, 3),     // 8 clocks/bit
    CAN_BIT_VALUE(5, 3, 3),     // 9 clocks/bit
    CAN_BIT_VALUE(5, 4, 4),     // 10 clocks/bit
    CAN_BIT_VALUE(6, 4, 4),     // 11 clocks/bit
    CAN_BIT_VALUE(6, 5, 4),     // 12 clocks/bit
    CAN_BIT_VALUE(7, 5, 4),     // 13 clocks/bit
    CAN_BIT_VALUE(7, 6, 4),     // 14 clocks/bit
    CAN_BIT_VALUE(8, 6, 4),     // 15 clocks/bit
    CAN_BIT_VALUE(8, 7, 4),     // 16 clocks/bit
    CAN_BIT_VALUE(9, 7, 4),     // 17 clocks/bit
    CAN_BIT_VALUE(9, 8, 4),     // 18 clocks/bit
    CAN_BIT_VALUE(10, 8, 4)     // 19 clocks/bit
};