Interacting with i.MX6UL EVK sensors

The imx6ulevk baseboard includes the following NXP sensors connected to the I2C1 bus.

• MAG3110: High Accuracy, 3D Magnetometer
• FXLS8471Q: ±2g/±4g/±8g, Low g, 14-Bit Digital Accelerometer

This post shows how to enable the sensors and read their data using the Linux terminal.

This tutorial is based in the tag rel_imx_4.1.15_2.0.0_ga on linux-imx repository.

Configuring kernel to add the sensors

In menu configuration or in the defconfig file enable the sensors driver. (This step is not necessary when building with imx_v7_defconfig):

SENSORS_MAG3110
 Device Drivers > Hardware Monitoring support > Freescale MAG3110 e-compass
sensor

SENSOR_FXLS8471
 Device Drivers > Input device support > Generic input layer > Miscellaneous
devices > FXLS8471 motion sensor device driver.

Enabling the sensors

The sensors are disabled by default, once your board is running it’s necessary to enable the sensors by running the following command lines:

Enabling MAG3110 eCOMPASS:
root@imx6ulevk:~# echo 1 > /sys/devices/virtual/input/input3/enable

Enabling FXLS8471Q accelerometer:
root@imx6ulevk:~# echo 1 > /sys/devices/virtual/misc/FreescaleAccelerometer/enable
mma enable setting actived

Reading sensors data

The sensors can be tested in the Linux terminal through evtest or by reading the sensors raw data. Run the commands below and move your board in different directions to interact with the sensor.

Reading MAG3110 eCOMPASS through evtest

During this example, please use the board as a compass. The outputted coordinates (x,y,z) represent the vector pointing to the North.

root@imx6ulevk:~# evtest /dev/input/event3

Input driver version is 1.0.1
Input device ID: bus 0x18 vendor 0x0 product 0x0 version 0x0
Input device name: "mag3110"
Supported events:
  Event type 0 (EV_SYN)
  Event type 3 (EV_ABS)
    Event code 0 (ABS_X)
      Value   -987
      Min   -15000
      Max    15000
    Event code 1 (ABS_Y)
      Value   -921
      Min   -15000
      Max    15000
    Event code 2 (ABS_Z)
      Value    519
      Min   -15000
      Max    15000
Properties:
Testing ... (interrupt to exit)
Event: time 1476799745.395772, type 3 (EV_ABS), code 1 (ABS_Y), value -929
Event: time 1476799745.395772, type 3 (EV_ABS), code 2 (ABS_Z), value 524
Event: time 1476799745.395772, -------------- SYN_REPORT ------------
Event: time 1476799745.517924, type 3 (EV_ABS), code 0 (ABS_X), value -933
Event: time 1476799745.517924, type 3 (EV_ABS), code 1 (ABS_Y), value -931
Event: time 1476799745.517924, type 3 (EV_ABS), code 2 (ABS_Z), value 513
Event: time 1476799745.517924, -------------- SYN_REPORT ------------
Event: time 1476799745.636064, type 3 (EV_ABS), code 0 (ABS_X), value -863
Event: time 1476799745.636064, type 3 (EV_ABS), code 1 (ABS_Y), value -968
Event: time 1476799745.636064, type 3 (EV_ABS), code 2 (ABS_Z), value 495

Reading FXLS8471Q accelerometer raw data

As an alternative to evtest the sensors raw data can be read, for this example we are going to use a loop to read the data every 0.5s.

The value measured is the acceleration at each coordinate.

root@imx6ulevk:~# while true; do usleep 500000 | cat
/sys/devices/virtual/misc/FreescaleAccelerometer/data; done
240,64,-16496
256,48,-16512
224,64,-16424
392,-984,-17400
-3760,24,-7896
-2016,-7088,-10208
2360,2776,-15864
376,-256,-14448
176,-40,-16528
304,-32,-15944