ADXL355 no-OS driver#

Supported Devices#

ADXL355

Overview#

The digital output ADXL355 is low noise density, low 0 g offset drift, low power, 3-axis accelerometer with selectable measurement ranges. The ADXL355 supports the ±2 g, ±4 g, and ±8 g ranges. The ADXL355 offer industry leading noise, minimal offset drift over temperature, and long-term stability enabling precision applications with minimal calibration.

Highly integrated in a compact form factor, the low power ADXL355 is ideal in an Internet of Things (IoT) sensor node and other wireless product designs.

The ADXL355 multifunction pin names may be referenced by their relevant function only for either the serial peripheral interface (SPI) or I2C interface.

Applications#

  • Inertial measurement units (IMUs)/altitude and heading reference systems (AHRS)

  • Platform stabilization systems

  • Structural health monitoring

  • Seismic imaging

  • Tilt sensing

  • Robotics

  • Condition Monitoring

ADXL355 Device Configuration#

Driver Initialization#

In order to be able to use the device, you will have to provide the support for the communication protocol (SPI or I2C) as mentioned above.

The first API to be called is adxl355_init. Make sure that it returns 0, which means that the driver was initialized correctly.

After, it is recommended to perform a soft reset, by calling adxl355_soft_reset, in order to put the device in a known state.

Range Configuration#

By default, the device uses +/- 2g range configuration. You may modify this value to +/- 4g or +/- 8g by using adxl355_set_range API.

Filters Configuration#

The ADXL355 uses an analog, low-pass, antialiasing filter to reduce out of band noise and to limit bandwidth. The ADXL355 provides further digital filtering options to maintain optimal noise performance at various output data rates (ODRs). The default configuration for output data rate and low-pass filter corner is 4000Hz and 1000 Hz respectively. You may modify the ODR and low-pass filter configuration using adxl355_set_odr_lpf API.

The ADXL355 also includes an optional digital high-pass filter with a programmable corner frequency. By default, the high-pass filter is disabled. You may enable it with the desired configuration by using adxl355_set_hpf_corner API.

Axis Calibration Configuration#

You may set an offset for each axis for calibration purposes by using adxl355_set_offset.

The offset is disabled by default.

The data provided in adxl355_set_offset all be in two’s complement format.

The offset is added after all other signal processing is taking place.

FIFO Configuration#

There are 96 locations in the FIFO. Each location contains an acceleration data point on an axis.

In case you want to use the FIFO, you are able to modify the number of FIFO samples to be stored in the FIFO. The default and maximum value is 96, but can be modified using adxl355_set_fifo_samples API.

Activity Detection Configuration#

In case you want to use the activity detection algorithm, you can enable this feature on any axis using adxl355_conf_act_en API. By default the activity detection feature is disabled.

If activity detection feature is enabled, you will also have to specify a threshold for the activity detection using adxl355_conf_act_thr API and a number of consecutive measurements above the threshold which would trigger the detection of an activity. This number has to be set using adxl355_set_act_cnt_reg. The default value is 1.

Interrupts Configuration#

The device allows the usage of interrupts which can be mapped to INT1 or INT2 pins.

In case you want to use interrupts, make sure you configure the interrupt map by using adxl355_config_int_pins API. You may also configure the polarity of the interrupt, whether is active high or active low, by using adxl355_set_int_pol API.

The following events can be mapped to the interrupt pins:

  • DATA READY interrupt - it is triggered when new acceleration data is available to the interface and it is cleared on a read of the status register, using adxl355_get_sts_reg API.

  • FIFO FULL interrupt - it is triggered when the entries in the FIFO are equal to the setting made when calling adxl355_set_fifo_samples API. It is cleared when the number of entries in the FIFO is less than the number of samples indicated by adxl355_get_nb_of_fifo_entries API, which is only the case if sufficient data is read from the FIFO. It can also be cleared on a read of the status register, using adxl355_get_sts_reg API, but only when the entries in the FIFO are less than the value returned by adxl355_get_nb_of_fifo_entries API.

  • FIFO OVERFLOW interrupt - it is triggered when the FIFO is so far overrange that data is lost. The specified side of the FIFO is 96 locations. The interrupt is triggered only when there is an attempt to write past this 96-location limit. A read to the status register, using adxl355_get_sts_reg API clears the interrupt.

  • ACTIVITY interrupt - it is set when the measured acceleration on any axis is above the set threshold, using adxl355_conf_act_thr API for a number of consecutive measurement, equal with the value set using adxl355_set_act_cnt_reg API. A read of the status register, using adxl355_get_sts_reg API clears the interrupt, but this interrupt is triggered again at the end of the next measurement if the activity conditions are still satisfied.

ADXL355 Device Measurements#

Operation Mode Setting#

After the specific configuration was performed as mentioned above, you can set the device in the desired measurement mode, using adxl355_set_op_mode API. The available operation modes for measurement are as follows:

  • ADXL355_MEASUREMENT_TEMP_ON_DRDY_ON - measurement mode, with temperature measurement enabled and data ready pin functionality enabled.

  • ADXL355_MEASUREMENT_TEMP_OFF_DRDY_ON - measurement mode, with temperature measurement disabled and data ready pin functionality enabled.

  • ADXL355_MEASUREMENT_TEMP_ON_DRDY_OFF - measurement mode, with temperature measurement enabled and data ready pin functionality disabled.

  • ADXL355_MEASUREMENT_TEMP_OFF_DRDY_OFF - measurement mode, with temperature measurement disabled and data ready pin functionality disabled.

Temperature Data#

In case the operation mode selected includes the temperature measurement, then data can be obtained by calling adxl355_get_temp API. The temperature is in millidegrees Celsius, with scaling already applied.

If you want to obtain the raw temperature data without any scaling applies, simply call adxl355_get_raw_temp API.

Acceleration Data#

Single Data Set#

If you want to obtain a single data set, you may use adxl355_get_xyz API to obtain the data converted to g, or adxl355_get_raw_xyz API to obtain the raw data. The raw data is in two’s complement format and it does not have the scaling applied.

FIFO Data#

If you want to read from the FIFO, you may use adxl355_get_fifo_data API to obtain the data converted to g, or adxl355_get_raw_fifo_data api to obtain the raw data. The raw data is in two’s complement format and it does not have the scaling applied.

The parameter fifo_entries shows the number of valid measurements in the FIFO which were read.

ADXL355 Driver Initialization Example#

SPI Communication Example#

struct adxl355_dev *adxl355;
// Particular SPI configuration
struct no_os_spi_init_param sip = {
        .max_speed_hz = 10000000,
        .bit_order = SPI_BIT_ORDER_MSB_FIRST,
        .mode = SPI_CPOL0_SPI_CPHA0,
};
struct adxl355_init_param init_data_adxl355 = {
        .comm_init.spi_init = sip,
        .comm_type = ADXL355_SPI_COMM,
};

ret = adxl355_init(&adxl355, init_data_adxl355);
if (ret < 0)
        goto error;
ret = adxl355_soft_reset(adxl355);
if (ret < 0)
        goto error;
ret = adxl355_set_odr_lpf(adxl355, ADXL355_ODR_4000HZ);
if (ret < 0)
        goto error;
ret = adxl355_set_op_mode(adxl355, ADXL355_MEAS_TEMP_ON_DRDY_OFF);
if (ret < 0)
        goto error;

// Read single accel data
struct adxl355_frac_repr x;
struct adxl355_frac_repr y;
struct adxl355_frac_repr z;

ret = adxl355_get_xyz(adxl355,&x[0], &y[0], &z[0]);
if (ret < 0)
        goto error;

// Read FIFO accel data
struct adxl355_frac_repr x[32] = {0};
struct adxl355_frac_repr y[32] = {0};
struct adxl355_frac_repr z[32] = {0};
uint8_t fifo_entries = 0;
ret = adxl355_get_fifo_data(adxl355, &fifo_entries,
                            &x[0], &y[0], &z[0]);
if (ret < 0)
        goto error;

// Read temperature data
struct adxl355_frac_repr temp;
ret = adxl355_get_temp(adxl355, &temp);
if (ret < 0)
        goto error;

ADXL355 no-OS IIO support#

The ADXL355 IIO driver comes on top of ADXL355 driver and offers support for interfacing IIO clients through IIO lib.

ADXL355 IIO Device Configuration#

Device Attributes#

ADXL355 IIO device does not have any device specific attributes.

Device Channels#

ADXL355 IIO device has 0 output channels and 4 input channels: 3 acceleration channels and 1 temperature channel.

Acceleration channels#

The acceleration channels are:

  • Channel 0: accel_x

  • Channel 1: accel_y

  • Channel 2: accel_z

Each acceleration channel has 7 attributes. 5 of these attributes are shared in value with the other acceleration channels and 2 of these attributes can have different values for each channel.

The attributes are:

  • calibbias - offset added to the axis after all other signal processing. The calibbias value will be applied as an offset to the raw value bits [19:4]. See formula bellow.

  • filter_high_pass_3db_frequency (shared) - is the current setting for the high pass filter corner frequency. This value is common for all three acceleration channels and the value is influenced by the current sampling frequency (see table below).

  • filter_high_pass_3db_frequency_available (shared) - is the list of available high pass filter corner frequency values. This list is common for all three acceleration channels and the values are influenced by the current sampling frequency (see table below).

  • raw - is the raw acceleration value read from the device.

  • sampling_frequency (shared) - is the sampling frequency for acceleration data. This value is common for all three acceleration channels.

  • sampling_frequency_available (shared) - is the list of available sampling frequency values. This list is common for all three acceleration channels.

  • scale (shared) - is the scale that has to be applied to the raw value in order to obtain the converted real value in m/s^2 (see formula below). It has a constant value equal to: 0.000038245.

Sampling frequency (Hz)

High Pass Filter Corner Frequency available values (Hz)

4000.000000

0.000000

9.880000

2.483360

0.621800

0.154480

0.038160

0.009520

2000.000000

0.000000

4.940000

1.241680

0.310900

0.077240

0.019080

0.004760

1000.000000

0.000000

2.470000

0.620840

0.155450

0.038620

0.009540

0.002380

500.000000

0.000000

1.235000

0.310420

0.077725

0.019310

0.004770

0.001190

250.000000

0.000000

0.617500

0.155210

0.038862

0.009655

0.002385

0.000595

125.000000

0.000000

0.308750

0.077605

0.019431

0.004827

0.001192

0.000297

62.500000

0.000000

0.154375

0.038802

0.009715

0.002413

0.000596

0.000148

31.250000

0.000000

0.077187

0.019401

0.004857

0.001206

0.000298

0.000074

15.625000

0.000000

0.038593

0.009700

0.002428

0.000603

0.000149

0.000037

7.813000

0.000000

0.019298

0.004850

0.001214

0.000301

0.000074

0.000018

3.906000

0.000000

0.009647

0.002425

0.000607

0.000150

0.000037

0.000009

In order to obtain the value in the m/s^2 units, raw has to be scaled by scale:

converted_accel [m/s^2] = (raw + calibbias << 4) * scale
converted_accel [m/s^2] = (raw + calibbias << 4) * 0.000038245

Temperature channel#

The temperature channel is:

  • Channel 4: temp

The channel has 3 attributes, as follows:

  • offset - is the offset that has to be applied to the raw value in order to obtain the converted real value in degrees Celsius (see formula below). It has a constant value equal to -2111.250000.

  • raw - is the raw temperature value read from the device.

  • scale - is the scale that has to be applied to the raw value in order to obtain the converted real value in degrees Celsius (see formula below). It has a constant value equal to: -110.497238.

In order to obtain the value in the degrees Celsius units, offset has to be added to raw prior to scaling by scale:

converted_temp [degrees Celsius] = (raw + offset) * scale
converted_temp [degrees Celsius] = (2111.25 - raw) * 110.497238

Device buffers#

The ADXL355 IIO devices driver supports the usage of a data buffer for reading purposes.

ADXL355 IIO Driver Initialization Example#

#define DATA_BUFFER_SIZE 400
uint8_t iio_data_buffer[DATA_BUFFER_SIZE*4*sizeof(int)];

struct adxl355_iio_dev *adxl355_iio_desc;
struct adxl355_iio_init_param adxl355_init_par;

// Particular SPI configuration
struct no_os_spi_init_param sip = {
        .max_speed_hz = 10000000,
        .bit_order = SPI_BIT_ORDER_MSB_FIRST,
        .mode = SPI_CPOL0_SPI_CPHA0,
};

struct iio_data_buffer accel_buff = {
        .buff = (void *)iio_data_buffer,
        .size = DATA_BUFFER_SIZE*4*sizeof(int)
};

struct adxl355_init_param init_data_adxl355 = {
        .comm_init.spi_init = sip,
        .comm_type = ADXL355_SPI_COMM,
};

ret = adxl355_iio_init(&adxl355_iio_desc, &adxl355_init_par);
if (ret != SUCCESS)
        return ret;

struct iio_app_device iio_devices[] = {
        {
                .name = "adxl355",
                .dev = adxl355_iio_desc,
                .dev_descriptor = adxl355_iio_desc->iio_dev,
                .read_buff = &accel_buff,
                .write_buff = NULL
        }
};

return iio_app_run(iio_devices, NO_OS_ARRAY_SIZE(iio_devices));