LSM6DSV IMU sensor hub with external 3-axis 18-bit high precision magnetometer sensor

[NWang.1]

Hello,

We want to use LSM6DSV IMU sensor with external 3-axis 18-bit high-precision magnetometer sensor through IMU sensor hub function also with its FIFO function. We refer to following LSM6DSV sensor hub example:

https://github.com/STMicroelectronics/STMems_Standard_C_drivers/blob/master/lsm6dsv_STdC/examples/lsm6dsv_sensor_hub.c

We found that we can't get 3-axis 18-bit (3 x 3 = 9 bytes) mag sensor data from above example. It seemed that we can only get 3-axis 16-bit (3 x 2 = 6 bytes) through sensor hub with FIFO function. Because our total sensor data size has 9 bytes more than 6 bytes, we don't know how to use sensor hub to get 9 bytes mag sensor data with LSM6DSV. Could you give us some suggestion to acquire 9 bytes data from sensor hub or workaround method? 

Thank you very much.

Nan

[Federica Bossi]

Hi @NWang.1 ,

Unfortunately we don't have an example with a 3-axis 18bit, however you will have to put 3 bytes to read for the 18 bits and then as subadd you will have to put the register from which the data starts. If the data are non-contiguous, you could configure several readings separated by the right points.

[NWang.1]

Hi Bossi,

Thank you for your information. For our purpose, we want to acquire 3-axis(18-bit data for each axis) 9 bytes at once. We use following code to initialize IMU:

sh_cfg_read.slv_add = (MAGNETOMETER_SLAVE_ADDR & 0xFEU) >> 1; /* 7bit I2C address */
sh_cfg_read.slv_subadd = MAG_REG_HXL;  
sh_cfg_read.slv_len = 6;   // HXL,HXM,HXH,HYL,HYM,HYH,HZL,HZM,HZH
lsm6dsv_sh_slv_cfg_read(&dev_ctx, 0, &sh_cfg_read);
lsm6dsv_fifo_sh_batch_slave_set(&dev_ctx, 0, PROPERTY_ENABLE);

Then we want to acquire 9 bytes mag sensor data from while loop or drdy interrupt signal.

int imu_sensor_data_poll()
{
    ...
    ret = lsm6dsv_fifo_status_get(&dev_ctx, &fifo_status);
    num = fifo_status.fifo_level;
    while (num--) 
    {
         /* Read FIFO sensor value */
	 lsm6dsv_fifo_out_raw_get(&dev_ctx, &f_data);
         switch (f_data.tag) 
	 {
             case LSM6DSV_SENSORHUB_SLAVE0_TAG:
                 // Here We want to handle 9 bytes mag sensor data
             break;
             ......
         }
    }
    ...
}

But we found that the above code slv_len(Slave0_numop[2:0]) shouldn't exceed 7 according to following figure from datasheet:

What does this sentence "If the data are non-contiguous, you could configure several readings separated by the right points." mean? Can you provide some more detail information about it? Thank you very much.

[NWang.1]

Hi, ST guys:

Can we initialize sensor hub function to read 3-axis 18bit mag data on LSM6DSV IMU as following code:

......
# Note connect only one mag sensor but use same address
sh_cfg_read.slv_add = (MAGNETOMETER_SLAVE_ADDR & 0xFEU) >> 1; /* 7bit I2C address */
sh_cfg_read.slv_subadd = REG_ST1;   // Read fix 6 bytes for status and X,Y axis
sh_cfg_read.slv_len = 6;
lsm6dsv_sh_slv_cfg_read(&dev_ctx, 0, &sh_cfg_read);
lsm6dsv_fifo_sh_batch_slave_set(&dev_ctx, 0, PROPERTY_ENABLE);

sh_cfg_read.slv_add = (MAGNETOMETER_SLAVE_ADDR & 0xFEU) >> 1; /* 7bit I2C address */
sh_cfg_read.slv_subadd = REG_HYH;   // Read remaining 6 bytes for Z axis and status
sh_cfg_read.slv_len = 6;
lsm6dsv_sh_slv_cfg_read(&dev_ctx, 1, &sh_cfg_read);
lsm6dsv_fifo_sh_batch_slave_set(&dev_ctx, 1, PROPERTY_ENABLE);
......

imu_sensor_data_poll()
{
   ......
   while (num--) {
      switch(f_data.tag)
      {
          ......
          case LSM6DSV_SENSORHUB_SLAVE0_TAG:
             // Get mag sensor first 6 bytes data for status and X, Y axis 
             break;
          case LSM6DSV_SENSORHUB_SLAVE1_TAG:
             // Get mag sensor remaining 6 bytes for Z axis and status
             break;
      }
   }
}

Can we use above method to acquire 12 bytes data from mag sensor? Thank you very much. Note: We have only one mag sensor.

BRs.