RTOS/LAUNCHXL-CC2650: ADXL345 - Some problem with I2C transaction

Tool/software: TI-RTOS

Hello everyone,

I'm having a very similar issue like in this post (https://e2e.ti.com/support/embedded/tirtos/f/355/t/538836) except that I'm using CC2650 connects with ADXL345 via I2C interface. My first read/write transaction always fails and I have to send a dummy transaction as a work-around. After my first transaction, my other transactions that write/read to registers works properly. Unfortunately, that post is pretty old, so I don't know if the OP finds out the solution for this or not. Does anyone experience with the same issue or know what cause this?

I ran a couple tests to make sure that my CC2650 and ADXL345 can communicate properly, including a 'read' transaction to get the device id, and it returns the value of 0xE5 (correct as stated in the data sheet).

At this moment, I'm trying to find the solution as I mentioned above and also implement a function to read raw input data of 3 axis x, y ,z and converts it to g,

void ADXL345_GetGxyz(float* x,
             float* y,
             float* z)
{
    System_printf("\t%s IS CALLED\n", __FUNCTION__); System_flush();
    unsigned short xData = 0;  // X-axis's output data.
    unsigned short yData = 0;  // Y-axis's output data.
    unsigned short zData = 0;  // Z-axis's output data.

    ADXL345_GetXyz(&xData, &yData, &zData);
    *x = (float)(fullResolutionSet ? (xData * ADXL345_SCALE_FACTOR) :
            (xData * ADXL345_SCALE_FACTOR * (selectedRange >> 1)));
    *y = (float)(fullResolutionSet ? (yData * ADXL345_SCALE_FACTOR) :
            (yData * ADXL345_SCALE_FACTOR * (selectedRange >> 1)));
    *z = (float)(fullResolutionSet ? (zData * ADXL345_SCALE_FACTOR) :
            (zData * ADXL345_SCALE_FACTOR * (selectedRange >> 1)));
}

void ADXL345_GetXyz(unsigned short* x,
            unsigned short* y,
            unsigned short* z)
{
    System_printf("\t%s IS CALLED\n", __FUNCTION__); System_flush();
    *x = ADXL345_GetRegisterValue(ADXL345_DATAX1) << 8;
    *x += ADXL345_GetRegisterValue(ADXL345_DATAX0);
    *y = ADXL345_GetRegisterValue(ADXL345_DATAY1) << 8;
    *y += ADXL345_GetRegisterValue(ADXL345_DATAY0);
    *z = ADXL345_GetRegisterValue(ADXL345_DATAZ1) << 8;
    *z += ADXL345_GetRegisterValue(ADXL345_DATAZ0);
}

uint32_t ADXL345_GetRegisterValue(uint32_t registerAddress)
{
    System_printf("\t%s IS CALLED\n", __FUNCTION__); System_flush();
    uint32_t readData[2] = {0};
    uint32_t writeData[2] = {0};
    uint32_t registerValue = 0;

    I2C_Transaction i2cTransaction;
    // set up transaction
    writeData[0] = registerAddress;
    i2cTransaction.slaveAddress = ADXL345_ADDRESS;
    i2cTransaction.writeBuf = writeData;
    i2cTransaction.writeCount = 1;
    i2cTransaction.readBuf = readData;
    i2cTransaction.readCount = 1;

    if (I2C_transfer(i2c, &i2cTransaction)){
        registerValue = readData[0];
        System_printf("We received this 1 byte from ACC: %04x\n", registerValue); System_flush();
        System_printf("Read Work \n"); System_flush();
    } else {
        System_printf("I2C Bus fault .... Read Register Function \n");
        System_flush();
    }
    return registerValue;

}

But calling ADXL_GetGxyz only give me the same value of X Y Z: c083 9d8b 1759 although I tried to move the accelerometer with different positions? What did I possibly do wrong?

Any help would be greatly appreciated. Thanks,

Henry