How to interface NXP FXAS2100X gyroscope with the VisionSOM-6ULL

How to interface NXP FXAS2100X gyroscope with the VisionSOM-6ULL

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Description

FXAS2100x is a triple-axis digital gyroscope with 16-bit resolution and adjustable range from 250°/s to 2000°/s, and up to 800 Hz sample rate. In the example, we will use the FRDM-STBC-AGM01 module to show how to communicate with this sensor on the I²C bus.

Prerequisites

This tutorial is based on a pre-prepared image for VisionSOM-6ULL module. The image is available here: SoMLabs-VisionSOM-6ULL-training-02-2018-sdcard-2gb.zip.

Then you need to write the image file to microSD card. More information you can find in manuals: How to prepare SD Card with Debian 9.2 for VisionSOM-6ULL on Linux or How to prepare SD Card with Debian 9.2 for VisionSOM-6ULL on Windows. Please remember to use a proper image file: SoMLabs-VisionSOM-6ULL-training-02-2018-sdcard-2gb.zip.

In the ready-to-use OS image, the kernel driver for the gyroscope has already been enabled in the kernel config, and the device has been added to the devicetree.

If you want to enable the sensor's driver in the kernel by yourself, the following options have to be selected:

Device Drivers  --->
	Misc devices  --->
		<*> Freescale FXAS2100X gyroscope sensor

The gyroscope needs to be declared in the devicetree:

&i2c2 { 
    status = "okay"; 
    fxas2100x@20 {
         compatible = "fsl,fxas2100x"; 
         reg = <0x20>; 
      };
};

For more info how to customize, build and upload Device Tree file, please visit How to customize Debian 9.2 device tree.

Hardware set-up

Do not connect the shield to the Arduino-style connector on VisionCB. The connector on VisionCB has a 5V supply and uses 5V logic. The shield accepts only 3.3V.

Firstly, make sure the jumpers J6 and J7 are both set to positions 1-2:

Connect the FRDM-STBC-AGM01 module according to the photo below:

Reading the values

To run the gyroscope, you need to enable it:

root@localhost:~# cd fxas2100x
root@localhost:~/fxas2100x# ./fxas2100x_enable.sh
[ 1470.052799] misc FreescaleGyroscope: mma enable setting active 

and then, you should build and run the test application:

root@localhost:~/fxas2100x# make
make: Warning: File 'Makefile' has modification time 2963329 s in the future
cc -Wall -O0 -g -funsigned-char -I.  -c fxas2100x.c -o fxas2100x.o
cc -g -O0 -Wl,--gc-sections,--relax -L/usr/local/lib -lnfc_nci_linux -lpthread fxas2100x.o -o gyro-i2c
make: warning:  Clock skew detected.  Your build may be incomplete.

Now, it's time to run the application. The readings of three axis values will be displayed after executing:

root@localhost:~/fxas2100x# ./gyro-i2c 
0.0 0.0 0.0
0.1 0.0 -3.0
-0.3 0.3 -6.9
^C
root@localhost:~/fxas2100x# 

Any move of the sensor board will be related with the readings changes: