NOV_B-RAWDMI (Deprecated)

To send wheelspeed data through UART, please ensure the correct baud rate is set up. For more information on the UART port configuration, please refer to section 5.4.1 of the Integration Manual.

For streaming wheelspeed information via the UART serial or TCP ports, the message format NOV_B-RAWDMI, introduced by Fixposition, is used. The message format is as follows:

Framing:

The structure of the NOV_B-RAWDMI message frame is:

Measurement types (dmi1_type, dmi2_type, dmi3_type and dmi4_type):

The checksum is a 32 bit cyclic redundancy check (CRC) with the polynomial 0x04c11db7.

Notes:

• All fields are little-endian

• Signed fields are 2’s complement

• Possible integer types are: int8_t, uint8_t, int16_t, uint16_t, int32_t, uint32_t, int64_t, uint64_t

• Possible float types are: float (32 bits) and double (64 bits), as per IEEE 754

As a struct:

/**
 * @brief NOV_B-RAWDMI payload
 *
 * See https://docs.novatel.com/OEM7/Content/SPAN_Logs/RAWDMI.htm
 */
struct NovbRawdmi {  // clang-format off
    int32_t  dmi1;            //!< DMI1 value (RC wheel or FR wheel)
    int32_t  dmi2;            //!< DMI2 value (FL wheel or YW sensor)
    int32_t  dmi3;            //!< DMI3 value (RR wheel)
    int32_t  dmi4;            //!< DMI4 value (RL wheel)
    uint32_t dmi1_valid : 1;  //!< DMI1 value valid flag (1 = dmi1 value is valid)
    uint32_t dmi2_valid : 1;  //!< DMI2 value valid flag (1 = dmi2 value is valid)
    uint32_t dmi3_valid : 1;  //!< DMI3 value valid flag (1 = dmi3 value is valid)
    uint32_t dmi4_valid : 1;  //!< DMI4 value valid flag (1 = dmi4 value is valid)
    uint32_t dmi1_type  : 7;  //!< DMI1 value type (0 = linear speed, 1 = angular velocity)
    uint32_t dmi2_type  : 7;  //!< DMI2 value type (0 = linear speed, 1 = angular velocity)
    uint32_t dmi3_type  : 7;  //!< DMI3 value type (0 = linear speed, 1 = angular velocity)
    uint32_t dmi4_type  : 7;  //!< DMI4 value type (0 = linear speed, 1 = angular velocity)
};  // clang-format on

static_assert(sizeof(NovbRawdmi) == 20, "");

Details:

The mask is divided into eight fields and determines which of the dmi1..4 values contain valid data and also the type of data the value is represented.

The dmiX_mask fields can be either 0 or 1, depending if the dmiX value is invalid or valid, respectively.

The dmiX_type is a 7-bit unsigned integer representing the type of represented value in the dmiX field. Currently, only two values are supported: 0 for a linear speed or 1 for an angular velocity.

Some example masks:

• 0x00000001 = dmi1 value is valid and represents a linear velocity

• 0x00000802 = dmi2 value is valid and represents an angular velocity

• 0x00000004 = dmi3 value is valid and represents a linear velocity

• 0x02000008 = dmi4 value is valid and represents an angular velocity

The dmi1…4 values are speed values in an arbitrary unit. The resolution should be chosen such that small movements produce a useful signal. Ideally, these values will come in [mm/s], and [mrad/s]. Coarse resolution, such as [km/h], will not work well, in particular at slow speeds.

• dmi1 is for RC wheel or FR wheel

• dmi2 is for FL wheel or YW sensor

• dmi3 is for RR wheel

• dmi4 is for RL wheel

An example message with hexdump of the binary data:

• dmi1 = 111 = 0x0000006f = 6f 00 00 00 (at offset 12)

• dmi2 = -22222 = 0xfffff752 = 32 a9 ff ff (at offset 16)

• dmi3 = 333333 = 0x00051615 = 15 16 05 00 (at offset 20)

• dmi4 = -44 = 0xffffffd4 = d4 ff ff ff (at offset 24)

• mask = 0x00000001 | 0x00000002 | 0x00000004 | 0x00000008 = 0x0000000f = 0f 00 00 00 (at offset 28)

0x0000 00000   aa 44 13 14  dd 08 00 00  00 00 00 00  6f 00 00 00
               ^^^^^^^^^^^constant header^^^^^^^^^^^  ^^^^dmi1^^^
0x0010 00016   32 a9 ff ff  15 16 05 00  d4 ff ff ff  0f 00 00 00
               ^^^^dmi2^^^  ^^^^dmi3^^^  ^^^^dmi4^^^  ^^^^mask^^^
0x0020 00032   69 9d 53 7b
               ^^checksum^

Code:

Here is an example implementation in C: make_nov_b_rawdmi.c