Help on SensorTag accelerometer resolution prolbem

Update: I changed the source code to let the accelerometer on all the time, then I got all six outputs successfully. I make it by putting the code below to the HalAccSetRange function in hal_acc.c file and delete the turn on/off code in the HalAccRead function

// Select this sensor
HalAccSelect();
//Turn off sensor first
HalSensorWriteReg(ACC_REG_ADDR_CTRL_REG1, &accSensorOff, sizeof(accSensorOff));
// Turn on sensor
HalSensorWriteReg(ACC_REG_ADDR_CTRL_REG1, &accSensorConfig, sizeof(accSensorConfig));

However, I am still confused why the accelerometer cannot work as the usual way (wake up - measure - sleep). Does anyone have any suggestion? I am new to this area, please point out if I made any mistakes and I will appreciate your help :)

Thank you.

Chunmeng

I think the issue lies with the power-up and start-up times. Since Vdd is not switched the power-up time is not an issue; however with a default Tilt Output Data Rate of 12.5Hz there is a start-up time from “PC1 set” to valid outputs of 81mSecs when RES=1 (ie. 12-bit mode). This may apply even when not specifically enabling the tilt timer and the delay in the supplied code is much shorter than this.

 

I’ve added an optional 12-bit mode, where FEATURE_ADC_12BIT can be added to Project->Options->C/C++ Compiler->Preprocessor::Defined Symbols for each project, eg _A and _B if using OAD:

 

// Optional resolution setting, use high-power (12-bit) or low-power (8-bit)

#if defined ( FEATURE_ACC_12BIT )

  #define ACC_REG_RESOLUTION           ACC_REG_CTRL_RES

#else

  #define ACC_REG_RESOLUTION           0

#endif

 

// Range +- 2G

#define ACC_REG_CTRL_ON_2G             ( ACC_REG_CTRL_PC | ACC_REG_RESOLUTION )

#define ACC_REG_CTRL_OFF_2G            (               0 | ACC_REG_RESOLUTION )

 

// Range +- 4G

#define ACC_REG_CTRL_ON_4G             ( ACC_REG_CTRL_PC | ACC_REG_CTRL_GSEL_LO | ACC_REG_RESOLUTION )

#define ACC_REG_CTRL_OFF_4G            (               0 | ACC_REG_CTRL_GSEL_LO | ACC_REG_RESOLUTION )

 

// Range +- 8G

#define ACC_REG_CTRL_ON_8G             ( ACC_REG_CTRL_PC | ACC_REG_CTRL_GSEL_HI | ACC_REG_RESOLUTION )

#define ACC_REG_CTRL_OFF_8G            (               0 | ACC_REG_CTRL_GSEL_HI | ACC_REG_RESOLUTION )

 

The data length needs to be set, depending on the compile option:

// Length of sensor data in bytes, 12-bit requires 2 bytes per axis

#if defined ( FEATURE_ACC_12BIT )

  #define ACCELEROMETER_DATA_LEN 6

#else

  #define ACCELEROMETER_DATA_LEN 3

#endif

 

TI also uses a local define the usage of which which needs to be checked:

#define SENSOR_SERVICE          ACCELEROMETER_SERVICE

#define SENSOR_DATA_LEN         ACCELEROMETER_DATA_LEN

 

Leading to potential bugs such as here:

// Characteristic Value: data

#if (SENSOR_DATA_LEN == 3)

static uint8 sensorData[SENSOR_DATA_LEN] = { 0, 0, 0};

#elif (SENSOR_DATA_LEN == 6)

static uint8 sensorData[SENSOR_DATA_LEN] = { 0, 0, 0, 0, 0, 0};

#endif

 

Compile-time asserts in C code can detect this kind of issue:

COMPILE_ASSERT(sizeof(sensorData) == ACCELEROMETER_DATA_LEN );

 

Using your suggestion on initialization:

 

/**************************************************************************************************

* @fn          HalAccSetRange

*

* @brief       Set the range of the accelerometer

*

* @param       range: HAL_ACC_RANGE_2G, HAL_ACC_RANGE_4G, HAL_ACC_RANGE_8G

*

* @return      None

*/

void HalAccSetRange(uint8 range)

{

  accRange = range;

 

  switch (accRange)

  {

  case HAL_ACC_RANGE_2G:

    accSensorConfig = ACC_REG_CTRL_ON_2G;

    accSensorOff = ACC_REG_CTRL_OFF_2G;

    break;

  case HAL_ACC_RANGE_4G:

    accSensorConfig = ACC_REG_CTRL_ON_4G;

    accSensorOff = ACC_REG_CTRL_OFF_4G;

    break;

  case HAL_ACC_RANGE_8G:

    accSensorConfig = ACC_REG_CTRL_ON_8G;

    accSensorOff = ACC_REG_CTRL_OFF_8G;

    break;

  default:

    // Should not get here

    break;

  }

#if defined ( FEATURE_ACC_12BIT )

  // Select this sensor

  HalAccSelect();

  // Turn off sensor

  HalSensorWriteReg(ACC_REG_ADDR_CTRL_REG1, &accSensorOff, sizeof(accSensorOff));

  // Turn on sensor

  HalSensorWriteReg(ACC_REG_ADDR_CTRL_REG1, &accSensorConfig, sizeof(accSensorConfig));

#endif

}

 

Keep HalAccRead() to the same as before for 8-bit mode, but changing to your suggestion plus reading 6 bytes in 16-bit mode:

 

/**************************************************************************************************

* @fn          HalAccRead

*

* @brief       Read data from the accelerometer - X, Y, Z - 6 bytes 16-bit

*

* @return      TRUE if valid data, FALSE if not

*/

bool HalAccRead(uint8 *pBuf )

{

  uint8 buf[ACCELEROMETER_DATA_LEN];

  bool success;

 

  // Select this sensor

  HalAccSelect();

 

  // Read the six registers

  success = HalSensorReadReg( ACC_REG_ADDR_XOUT_L, buf, sizeof(buf) );

  if (success)

  {

    // Result is already in LE, don't need to reverse bytes

    uint8 *pDst = pBuf, *pSrc = buf, Index;

    for (Index=0; Index < sizeof(buf); Index++)

    {

      *pDst++ = *pSrc++;

    }

  }

  return success;

}

 

 

I’ve added more detail to the description:

 

/* ------------------------------------------------------------------------------------------------

 *                                         Description

 * ------------------------------------------------------------------------------------------------

 */

// CTRL_REG1 - I2C Address: 0x1Bh

// ==============================

// Read/write control register that controls the main feature set

// ===== ===== ===== ===== ===== ===== ===== =====

// R/W   R/W   R/W   R/W   R/W   R/W   R/W   R/W  

// ===== ===== ===== ===== ===== ===== ===== =====

// PC1   RES   DRDYE GSEL1 GSEL0 TDTE  WUFE  TPE   Reset Value

// Bit7  Bit6  Bit5  Bit4  Bit3  Bit2  Bit1  Bit0  00000000

// ===== ===== ===== ===== ===== ===== ===== =====

//

// PC1 controls the operating mode of the KXTIK

//    PC1 = 0 - stand-by mode

//    PC1 = 1 - operating mode

// RES determines the performance mode of the KXTIK. Note that to change the value

// of this bit, the PC1 bit must first be set to 0

//    RES = 0 - low current, 8-bit valid

//    RES = 1 - high current, 12-bit valid

// DRDYE enables the reporting of the availability of new acceleration data on the

// interrupt. Note that to change the value of this bit, the PC1 bit must first be set to 0

//    DRDYE = 0 - availability of new acceleration data not reflected on interrupt pin (11)

//    DRDYE = 1 - availability of new acceleration data reflected on interrupt pin (11)

// GSEL1, GSEL0 selects the acceleration range of the accelerometer outputs per Table 12.

// Note that to change the value of this bit, the PC1 bit must first be set to 0

// ± 2g / 4g / 8g Tri-axis Digital

//

//    GSEL1 GSEL0  Range

//    ===== =====  =====

//      0      0   +/-2g

//      0      1   +/-4g

//      1      0   +/-8g

//      1      1      NA

//    Table 12. Selected Acceleration Range

//

// TDTE enables the Directional TapTM function that will detect single and double tap events.

// Note that to change the value of this bit, the PC1 bit must first be set to 0

//    TDTE = 0 - disable

//    TDTE = 1 - enable

// WUFE enables the Wake Up (motion detect) function that will detect a general motion event.

// Note that to change the value of this bit, the PC1 bit must first be set to 0

//    WUFE = 0 - disable

//    WUFE = 1 - enable

// TPE enables the Tilt Position function that will detect changes in device orientation.

// Note that to change the value of this bit, the PC1 bit must first be set to 0

//    TPE  = 0 - disable

//    TPE  = 1 - enable

 

// Accelerometer Registers

// =======================

// 1 - Read Back Acceleration Data - 8-bit

//   - Write 0x80 to Control Register 1 to assert PC1 (Power Control bit), set the G-range to

//     +/-2g, and set the resolution to 8 bits

//

//     Register Name     Address         Value

//         CTRL_REG1     0x1B  0001 1011 0x80 1000 0000

//   - Acceleration data can now be read from the XOUT_H, YOUT_H, and ZOUT_H registers.

// 2 - Read Back Acceleration Data - 16-bit

//   - Write 0x80 to Control Register 1 to assert PC1 (Power Control bit), set the G-range to

//     +/-2g, and set the resolution to 16 bits

//

//     Register Name     Address         Value

//         CTRL_REG1     0x1B  0001 1011 0xC0 1100 0000

//   - Acceleration data can now be read from the XOUT_L/H, YOUT_L/H, and ZOUT_L/H registers.

 

// Free-fall Sensing

// =================

// When a tri-axis accelerometer is stationary, its total acceleration it measures is 1g

// (9.8m/s2), regardless of orientation. This total acceleration can be calculated from

// the X, Y, and Z outputs of the accelerometer using Eq. 1 below. When a tri-axis

// accelerometer is dropped in any orientation, it is in free-fall and the measured

// acceleration on all three axes is 0g. Therefore, the total acceleration is zero

// as well. Total acceleration can be monitored to sense that the accelerometer has been

// dropped, and to measure its free-fall time. Note that this signature cannot accurately

// be observed when using a dual axis accelerometer because, when horizontally oriented,

// the X and Y-axis outputs are the same (0g), whether the accelerometer is stationary or

// in free-fall.

//

// Total Acceleration atot = root(ax^2 + ay^2 + az^2)

 

/* ------------------------------------------------------------------------------------------------

*                                           Constants

* ------------------------------------------------------------------------------------------------

*/

// Sensor I2C address

#define HAL_KXTI9_I2C_ADDRESS          0x0F

 

// KXTI9 register addresses

//                                                                      I2C Address

//      Register Name                  Addr    Register Name    * Rd/Wr Hex  Binary

//      ===========================    ====    ================ = ===== ==== =========

#define ACC_REG_ADDR_XOUT_HPF_L        0x00 // XOUT_HPF_L           R   0x00 0000 0000

#define ACC_REG_ADDR_XOUT_HPF_H        0x01 // XOUT_HPF_H           R   0x01 0000 0001

#define ACC_REG_ADDR_YOUT_HPF_L        0x02 // YOUT_HPF_L           R   0x02 0000 0010

#define ACC_REG_ADDR_YOUT_HPF_H        0x03 // YOUT_HPF_H           R   0x03 0000 0011

#define ACC_REG_ADDR_ZOUT_HPF_L        0x04 // ZOUT_HPF_L           R   0x04 0000 0100

#define ACC_REG_ADDR_ZOUT_HPF_H        0x05 // ZOUT_HPF_H           R   0x05 0000 0101

#define ACC_REG_ADDR_XOUT_L            0x06 // XOUT_L               R   0x06 0000 0110

#define ACC_REG_ADDR_XOUT_H            0x07 // XOUT_H               R   0x07 0000 0111

#define ACC_REG_ADDR_YOUT_L            0x08 // YOUT_L               R   0x08 0000 1000

#define ACC_REG_ADDR_YOUT_H            0x09 // YOUT_H               R   0x09 0000 1001

#define ACC_REG_ADDR_ZOUT_L            0x0A // ZOUT_L               R   0x0A 0000 1010

#define ACC_REG_ADDR_ZOUT_H            0x0B // ZOUT_H               R   0x0B 0000 1011

#define ACC_REG_ADDR_DCST_RESP         0x0C // DCST_RESP            R   0x0C 0000 1100

                                            // Not Used             -   0x0D 0000 1101

                                            // Not Used             -   0x0E 0000 1110

#define ACC_REG_ADDR_WHO_AM_I          0x0F // WHO_AM_I             R   0x0F 0000 1111

#define ACC_REG_ADDR_TILT_POS_CUR      0x10 // TILT_POS_CUR         R   0x10 0001 0000

#define ACC_REG_ADDR_TILT_POS_PRE      0x11 // TILT_POS_PRE         R   0x11 0001 0001

                                            // Kionix Reserved      -   0x12 0001 0010

                                            // Kionix Reserved      -   0x13 0001 0011

                                            // Kionix Reserved      -   0x14 0001 0100

#define ACC_REG_ADDR_INT_SRC_REG1      0x15 // INT_SRC_REG1         R   0x15 0001 0101

#define ACC_REG_ADDR_INT_SRC_REG2      0x16 // INT_SRC_REG2         R   0x16 0001 0110

                                            // Not Used             -   0x17 0001 0111

#define ACC_REG_ADDR_STATUS_REG        0x18 // STATUS_REG           R   0x18 0001 1000

                                            // Not Used             -   0x19 0001 1001

#define ACC_REG_ADDR_INT_REL           0x1A // INT_REL              R   0x1A 0001 1010

#define ACC_REG_ADDR_CTRL_REG1         0x1B // CTRL_REG1        *   R/W 0x1B 0001 1011

#define ACC_REG_ADDR_CTRL_REG2         0x1C // CTRL_REG2        *   R/W 0x1C 0001 1100

#define ACC_REG_ADDR_CTRL_REG3         0x1D // CTRL_REG3        *   R/W 0x1D 0001 1101

#define ACC_REG_ADDR_INT_CTRL_REG1     0x1E // INT_CTRL_REG1    *   R/W 0x1E 0001 1110

#define ACC_REG_ADDR_INT_CTRL_REG2     0x1F // INT_CTRL_REG2    *   R/W 0x1F 0001 1111

#define ACC_REG_ADDR_INT_CTRL_REG3     0x20 // INT_CTRL_REG3    *   R/W 0x20 0010 0000

#define ACC_REG_ADDR_DATA_CTRL_REG     0x21 // DATA_CTRL_REG    *   R/W 0x21 0010 0001

                                            // Not Used             -   0x22-0x27

#define ACC_REG_ADDR_TILT_TIMER        0x28 // TILT_TIMER       *   R/W 0x28 0010 1000

#define ACC_REG_ADDR_WUF_TIMER         0x29 // WUF_TIMER        *   R/W 0x29 0010 1001

                                            // Not Used             -   0x2A 0010 1010

#define ACC_REG_ADDR_TDT_TIMER         0x2B // TDT_TIMER        *   R/W 0x2B 0010 1011

#define ACC_REG_ADDR_TDT_H_THRESH      0x2C // TDT_H_THRESH     *   R/W 0x2C 0010 1100

#define ACC_REG_ADDR_TDT_L_THRESH      0x2D // TDT_L_THRESH     *   R/W 0x2D 0010 1101

#define ACC_REG_ADDR_TDT_TAP_TIMER     0x2E // TDT_TAP_TIMER    *   R/W 0x2E 0010 1110

#define ACC_REG_ADDR_TDT_TOTAL_TIMER   0x2F // TDT_TOTAL_TIMER  *   R/W 0x2F 0010 1111

#define ACC_REG_ADDR_TDT_LATENCY_TIMER 0x30 // TDT_LATENCY_TIME *   R/W 0x30 0011 0000

#define ACC_REG_ADDR_TDT_WINDOW_TIMER  0x31 // TDT_WINDOW_TIMER *   R/W 0x31 0011 0001

#define ACC_REG_ADDR_BUF_CTRL1         0x32 // BUF_CTRL1        *   R/W 0x32 0011 0010

#define ACC_REG_ADDR_BUF_CTRL2         0x33 // BUF_CTRL2        *   R/W 0x33 0011 0011

#define ACC_REG_ADDR_BUF_STATUS_REG1   0x34 // BUF_STATUS_REG1      R   0x34 0011 0100

#define ACC_REG_ADDR_BUF_STATUS_REG2   0x35 // BUF_STATUS_REG2      R ? 0x35 0011 0101

#define ACC_REG_ADDR_BUF_CLEAR         0x36 // BUF_CLEAR            W   0x36 0011 0110

                                            // Reserved             -   0x37-0x39

#define ACC_REG_ADDR_SELF_TEST         0x3A // SELF_TEST            R/W 0x3A 0011 1010

                                            // Reserved             -   0x3B-0x59

#define ACC_REG_ADDR_WUF_THRESH        0x5A // WUF_THRESH       *   R/W 0x5A 0101 1010

                                            // Reserved             -   0x5B 0101 1011

#define ACC_REG_ADDR_TILT_ANGLE        0x5C // TILT_ANGLE       *   R/W 0x5C 0101 1100

                                            // Reserved             -   0x5D-0x5E

#define ACC_REG_ADDR_HYST_SET          0x5F // HYST_SET         *   R/W 0x5F 0101 1111

#define ACC_REG_ADDR_BUF_READ          0x7F // BUF_READ             R   0x7F 0111 1111

 

// Select register valies

#define REG_VAL_WHO_AM_I               0x08 // (data sheet says 0x04)

 

// CTRL1 BIT MASKS

#define ACC_REG_CTRL_PC                0x80 // Power control  '1' On    '0' Off

#define ACC_REG_CTRL_RES               0x40 // Resolution     '1' High  '0' Low

#define ACC_REG_CTRL_DRDYE             0x20 // Data Ready     '1' On    '0' Off

#define ACC_REG_CTRL_GSEL_HI           0x10 // Range     '00' +/-2g    '01' +/-4g

#define ACC_REG_CTRL_GSEL_LO           0x08 //           '10' +/-8g    '11' N/A

#define ACC_REG_CTRL_GSEL_TDTE         0x04 // Directional Tap '1' On   '0' Off

#define ACC_REG_CTRL_GSEL_WUFE         0x02 // Wake Up         '1' On   '0' Off

#define ACC_REG_CTRL_GSEL_TPE          0x01 // Tilt Position   '1' On   '0' Off