I am trying to interface a LSM330 accelerometer/gyroscope module on an i.MX6 board. The module is connected to an I2C bus, the relevant parts of the device tree file are as follows:
&i2c1 {
clock-frequency = <100000>;
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_i2c1_2>;
status = "okay";
/* LSM330 motion detector (accelerometer) */
lsm330_accel: lsm330_accel@0x1e {
compatible = "st,lsm330-accel";
st,drdy-int-pin = <1>;
reg = <0x1e>;
};
/* LSM330 motion detector (gyroscope) */
lsm330_gyro: lsm330_gyro@0x6a {
compatible = "st,lsm330-gyro";
st,drdy-int-pin = <2>;
reg = <0x6a>;
};
};
The module shows up as /dev/iio:device0 for the accelerometer and /dev/iio:device1 for the gyroscope. They also show up as /sys/bus/iio/devices/iio:device0and /sys/bus/iio/devices/iio:device1. I can get the sensor readings via cat in_accel_x_raw etc. However, running cat /dev/iio:device0 immediately returns and produce no output.
After searching around the Internet, I also tried the commands:
cd /sys/bus/iio/devices/iio_sysfs_trigger
echo 0 > add_trigger
cd /sys/bus/iio/devices/iio:device0
echo 1 > scan_elements/in_accel_x_en
echo 1 > scan_elements/in_accel_y_en
echo 1 > scan_elements/in_accel_z_en
echo 1 > scan_elements/in_timestamp_en
echo sysfstrig0 > trigger/current_trigger
echo 100 > buffer/length
echo 1 > buffer/enable
echo 1 > /sys/bus/iio/devices/trigger0/trigger_now
This should set the channels, enable the buffer and get some readings into the buffer. As far as I know, cat /dev/iio:device0 should display the buffer, but it is giving me Device or resource busy. Further reads from the kernel with cat /sys/bus/iio/devices/iio:device0/in_accel_x_raw no longer works and give the same error message.
I am very new to the linux kernel, my goal is to expose the sensor data to the Android system so the user can rotate the screen etc. How do I get Android to obtain sensor readings from the module?
After looking at the android logcat, it turns out the Android HAL does not have permissions to read or write to the directories in the sysfs. I ended up putting a bunch of chmod commands in the init.rc file so Android can access the sensor data.
# Change permissions for the LSM330 sysfs entries (accelerometer)
chmod 0666 /sys/bus/iio/devices/iio\:device0/sampling_frequency
chmod 0666 /sys/bus/iio/devices/iio\:device0/buffer/enable
chmod 0666 /sys/bus/iio/devices/iio\:device0/buffer/length
chmod 0666 /sys/bus/iio/devices/iio\:device0/trigger/current_trigger
chmod 0666 /sys/bus/iio/devices/iio\:device0/scan_elements/in_accel_x_en
chmod 0666 /sys/bus/iio/devices/iio\:device0/scan_elements/in_accel_y_en
chmod 0666 /sys/bus/iio/devices/iio\:device0/scan_elements/in_accel_z_en
chmod 0666 /sys/bus/iio/devices/iio\:device0/scan_elements/in_timestamp_en
chmod 0666 /dev/iio\:device0
Hope this helps someone.