i2c_transfer() reads all zeros

[Learner]

Hello,

I am trying to read data from LS2DE12 accelerometer MEMS chip via I2C bus and I am seeing only zeros for all 3 axes.

I can write to the various registers successfully and read back their content to check the write was successful using this function.

static int32_t lis2de12_readb(uint8_t add, uint8_t *b)
{
    struct i2c_msg msgs[2];

    /* Send the address to read from */
    msgs[0].buf = &add;
    msgs[0].len = 1U;
    msgs[0].flags = I2C_MSG_WRITE | I2C_MSG_STOP;

    /* Read from device. STOP after this. */
    msgs[1].buf = b;
    msgs[1].len = 1U;
    msgs[1].flags = I2C_MSG_READ | I2C_MSG_STOP;

    return i2c_transfer(accelerometer.handle, &msgs[0], 2, LIS2DE12_I2C_ADD);
}

The above is called at initialisation to configure the various registers as shown in the snippets of code below, and all seems to be working ok...

accelerometer_t *lis2de12_initialise(void *dev)
{
    accelerometer.handle = dev;
    uint8_t b,d[8];

    accelerometer.moved = false;
    lis2de12_readb( LIS2DE12_WHO_AM_I,&d[0] );
    if ( d[0] != LIS2DE12_ID )
    {
        LOG_INF( "Fail LIS2" );
        return( NULL );
    }
    else
    {
        LOG_DBG( "OK LIS2" );
        accelerometer.present = true;

        lis2de12_writeb( LIS2DE12_CTRL_REG1, 0x2f ); //0x1f);
        lis2de12_readb( LIS2DE12_CTRL_REG1, &d[0] );
        if ( d[0] != 0x2f )
        {
            LOG_INF( "Fail LIS2" );
            return( NULL );
        }

        lis2de12_writeb( LIS2DE12_CTRL_REG4, 0x80 );
        lis2de12_readb( LIS2DE12_CTRL_REG4, &d[1] );
        if (d[1] != 0x80)
        {
            LOG_INF( "Fail LIS2" );
            return( NULL );
        }

        //High pass filter enabled
//      lis2de12_writeb(LIS2DE12_CTRL_REG2,0x40);

        // Normal mode + HPF cutoff freq 0.02 Hz @1 Hz ODR + Enable the internal filter
        lis2de12_writeb( LIS2DE12_CTRL_REG2,0xB8 );
        lis2de12_readb( LIS2DE12_CTRL_REG2,&d[2] );
        if ( d[2] != 0xB8 )
        {
            LOG_INF( "Fail LIS2" );
            return( NULL );
        }

        // Enable FIFO operation
        lis2de12_writeb( LIS2DE12_CTRL_REG5, 0x40 );
        lis2de12_readb( LIS2DE12_CTRL_REG5, &d[3] );
        if (d[3] != 0x40)
        {
            LOG_INF( "Fail LIS2" );
            return( NULL );
        }

        // Enable FIFO Mode
        lis2de12_writeb( LIS2DE12_FIFO_CTRL_REG, 0x40 );
        lis2de12_readb( LIS2DE12_FIFO_CTRL_REG, &d[4] );
        if (d[4] != 0x40)
        {
            LOG_INF( "Fail LIS2" );
            return( NULL );
        }

        LOG_DBG( "C1 %x:C4 %x:C2 %x:C5 %x:FIFO %x:",d[0],d[1],d[2],d[3],d[4] );
        k_sleep(K_MSEC(20));

        return( &accelerometer );
    }

}//lis2de12_initialise()

However, when I read the x,y,z data I am getting all zeros.

The function that reads the x,y,z data is shown below,

static int32_t lis2de12_read_fifo(uint8_t add, uint8_t *b)
{
    struct i2c_msg msgs[2];

    /* Send the address to read from */
    msgs[0].buf = &add;
    msgs[0].len = 1U;
    msgs[0].flags = I2C_MSG_WRITE | I2C_MSG_STOP;

    /* Read from device. STOP after this. */
    msgs[1].buf = b;
    msgs[1].len = 6U;
    msgs[1].flags = I2C_MSG_READ | I2C_MSG_STOP;

    return i2c_transfer(accelerometer.handle, &msgs[0], 2, LIS2DE12_I2C_ADD);
}

The above function lis2de12_read_fifo() is called from the function shown below which itself gets called from an executive loop running in a forever loop.

typedef struct accel{
            void        * handle;
            int16_t     x;
            int16_t     y;
            int16_t     z;
            uint32_t    vector;
            uint32_t    oldvector;
            uint8_t     present:1;
            uint8_t     moved:1;
            uint32_t    LastMovementTime;

        } accelerometer_t;

accelerometer_t accelerometer;

boolean_t lis2de12_getxyz(void)
{
    uint8_t     status;
    uint8_t     d[6],i;
    union {
            uint8_t  b[2];
            int16_t  i;
          } iandb;

    accelerometer.vector = accelerometer.oldvector;

    if (accelerometer.present)
    {
        lis2de12_readb( LIS2DE12_STATUS_REG, &status );
        if ( status & ZYX_DATA_READY )
        {
#if 0
            for ( i = 0; i < 6; i++ )
            {
                if ( lis2de12_readb( LIS2DE12_FIFO_READ_START + i, &d[i] ) != 0 )
                {
                    break;
                }
            }
            if ( i == 6 )
#endif //#if 0

            if ( lis2de12_read_fifo( LIS2DE12_FIFO_READ_START, d ) != 0 )
            {
                iandb.b[1] = d[0];
                iandb.b[0] = d[1];
                accelerometer.x = iandb.i;

                iandb.b[1] = d[2];
                iandb.b[0] = d[3];
                accelerometer.y = iandb.i;

                iandb.b[1] = d[4];
                iandb.b[0] = d[5];
                accelerometer.z = iandb.i;

                accelerometer.vector = (uint32_t)accelerometer.x * (uint32_t)accelerometer.x +
                                       (uint32_t)accelerometer.y * (uint32_t)accelerometer.y +
                                       (uint32_t)accelerometer.z * (uint32_t)accelerometer.z;
                
                printf( "[%u s] ", timer_GetOneSecondTime() ); //DBG
                printf( "STATUS_REG = 0x%02x acc_x = 0x%04x acc_y = 0x%04x acc_z = 0x%04x v = %d acc_oldv = %d\n",
                        status,
                        accelerometer.x, accelerometer.y, accelerometer.z,
                        accelerometer.vector,
                        accelerometer.oldvector                             );
            }
        }
        return true;
    }
    else
    {
        return false;
    }

}//lis2de12_getxyz()

 

Here is a sample of the debug output

[14 s] STATUS_REG = 0xff acc_x = 0x0000 acc_y = 0x0000 acc_z = 0x0000 v = 0 acc_oldv = 0
[15 s] STATUS_REG = 0xff acc_x = 0x0000 acc_y = 0x0000 acc_z = 0x0000 v = 0 acc_oldv = 0

[15 s] STATUS_REG = 0xff acc_x = 0x0000 acc_y = 0x0000 acc_z = 0x0000 v = 0 acc_oldv = 0
[15 s] STATUS_REG = 0xff acc_x = 0x0000 acc_y = 0x0000 acc_z = 0x0000 v = 0 acc_oldv = 0
[15 s] STATUS_REG = 0xff acc_x = 0x0000 acc_y = 0x0000 acc_z = 0x0000 v = 0 acc_oldv = 0
[15 s] STATUS_REG = 0xff acc_x = 0x0000 acc_y = 0x0000 acc_z = 0x0000 v = 0 acc_oldv = 0
[15 s] STATUS_REG = 0xff acc_x = 0x0000 acc_y = 0x0000 acc_z = 0x0000 v = 0 acc_oldv = 0

It must be something to do with the way I am reading the FIFO content because when I read individual registers content all seems to be OK.

Please advise.

Kind regards

Mohamed

[Simon]

Hello,

I'll take a look at this tomorrow.

Best regards,

Simon

[Learner]

Thank you Simon.

I am looking forward to read your findings.

Kind regards

Mohamed

[Simon]

Try setting struct i2c_msg msgs[2] to static, like shown below:

static int32_t lis2de12_read_fifo(uint8_t add, uint8_t *b)
{
    static struct i2c_msg msgs[2];

    /* Send the address to read from */
    msgs[0].buf = &add;
    msgs[0].len = 1U;
    .
    .

Do you have a logic analyzer? That is quite useful to see what's actually going on, on the lines. If you have one, could you you attach it to the SDA and SCL lines and upload the trace here?

Best regards,

Simon

[Learner]

Thank you Simon.

I tried your suggestion to make the struct declaration static but it did not make any difference.

Hooking up a logic analyser to SDA and SCL lines was going to be my next move but I was hoping you may be able to find what could be wrong in my code without resorting to a logic analyser. I am not suspecting the hardware, are you?

The reason I am saying this is because I can read the control and status registers content without any problem. If there was something wrong with the hardware setup it would have affected them too.

Anyway, I am working from home today and the logic analyser is in the office. So, I will do it on Monday and will give you some feedback.

Kind regards

Mohamed

[Simon]

Hey, did you capture a trace?

I'll take a closer look at this tomorrow.

What happens if you try to read the data in the same way it's done in the lis2ds12 driver, by using i2c_burst_read()?

https://github.com/nrfconnect/sdk-zephyr/blob/v2.6.99-ncs1/drivers/sensor/lis2ds12/lis2ds12_i2c.c#L28-L29