Enabling an Industrial I/O Driver on Raspberry Pi 3 running Arch Linux ARM

MPU9250 from TDK is a three in one Gyro + Accelerometer + Compass sensor with an I²C interface. Mainline Linux kernel has the source code for it's driver which reads values from the sensor via I²C and exposes it via the filesystem using the Industrial I/O subsystem. Arch Linux ARM for Raspberry Pi does not come with the driver for this pre-compiled and enabled. Here is how to compile and enable the driver on Raspberry Pi 3 Model B.

Raspberry Pi 3 Model B with MPU9250 connected to it's I2C interface
and a USB-Serial widget to access console over serial

Connections

Buy the MPU9250 Widget from Amazon and hook it up to your Raspberry Pi as per the table

RPi3 (2.54mm)	MPU9250 Module (2.54mm)
3.3V PWR Pin 1	VCC
GND Pin 9	GND
I2C1_SCL GPIO 3 Pin 5	SCL
I2C1_SDA GPIO 2 Pin 3	SDA
GPIO4 Pin 7	INT

Preparations

Prepare and boot Arch Linux ARM from SD Card: instructions are here.
Connect the Raspberry Pi to your home network using an ethernet cable.
Look up the DHCP assigned IP address from your router’s configuration web interface, it will show as a new device named "alarmpi".
Gain access to the console over SSH using PuTTY or MobaXterm or physically using keyboard/mouse/monitor. Login: alarm and Password: alarm
While following the instructions below, switch to root user whenever required using:

su root
Password: root

Enable Console over USB-Serial [Optional]

Follow instructions over at https://gist.github.com/yeokm1/d6c3ca927919c61257cd

Install required packages on Arch Linux ARM running on RPi3B

pacman-key --init
pacman-key --populate archlinuxarm
pacman -Syu
pacman -S curl bash ca-certificates nano i2c-tools jq iio-utils
pacman -S base-devel
pacman -S dtc git
pacman -S linux-raspberrypi-headers
pacman -S python python-pip

Enable I²C on Raspberry Pi 3 Model B running Arch Linux ARM

su root
nano /etc/modules-load.d/raspberrypi.conf
Append:

i2c-dev
Save and Reboot

nano /boot/config.txt
Append:

dtparam=i2c=on
Save and Reboot

Test (0x68 is MPU9250):

[root@alarmpi alarm]# i2cdetect -y 1

0 1 2 3 4 5 6 7 8 9 a b c d e f

00: -- -- -- -- -- -- -- -- -- -- -- -- --

10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

60: -- -- -- -- -- -- -- -- 68 -- -- -- -- -- -- --

70: -- -- -- -- -- -- -- --

Python Library for reading from MPU9250 over I²C

Install python packages (Latest version from its git repository, replace the version numbers with latest one)

python -m pip install git+https://github.com/FaBoPlatform/FaBo9AXIS-MPU9250-Python.git@78e4da28e176a07cc1c22c2f61a5be7ffe6c2c28

Clone the git repository to fetch the example code

git clone https://github.com/FaBoPlatform/FaBo9AXIS-MPU9250-Python.git

First test in text mode using example from FaBo9AXIS-MPU9250-Python repo (This uses raw I²C bus without the need for MPU9250 Industrial I/O Driver):

[root@alarmpi ~]# python FaBo9AXIS-MPU9250-Python/example/read9axis.py

ax = -0.871

ay = 0.39

az = 0.31

gx = -0.793

gy = 0.725

gz = -0.099

mx = 30.289

my = 44.197

mz = -24.791

ax = -0.872

ay = 0.392

az = 0.312

gx = -0.801

gy = 0.71

gz = -0.069

mx = 30.647

my = 43.475

mz = -25.832

Enabling MPU9250 Industrial I/O interface on ArchLinux running on Raspberry Pi 3

Fetch (from mainline kernel repository) the latest sources of inv-mpu6050 which has support for MPU9250 through shallow clone/sparse checkout, execute the following commands while in /root:

su root
mkdir linux_main_src
cd linux_main_src
git init
git remote add origin https://github.com/torvalds/linux.git
git config core.sparsecheckout true
echo "drivers/iio/*" >> .git/info/sparse-checkout
git pull --depth=3 origin master

Create the Makefile for compiling the driver:

Get into /root/linux_main_src/drivers/iio/imu/inv_mpu6050
And modify the Makefile present there for the inv_mpu6080 driver to compile on and for Raspberry Pi 3 platform (lines in blue will be present already, lines in red are the ones that need to be appended, make sure to use a single tab and not spaces at the beginning of the lines below “all:’ and “clean:”) :

Makefile

# SPDX-License-Identifier: GPL-2.0

# Makefile for Invensense MPU6050 device.

obj-$(CONFIG_INV_MPU6050_IIO) += inv-mpu6050.o

inv-mpu6050-y := inv_mpu_core.o inv_mpu_ring.o inv_mpu_trigger.o \

inv_mpu_aux.o inv_mpu_magn.o

obj-$(CONFIG_INV_MPU6050_I2C) += inv-mpu6050-i2c.o

inv-mpu6050-i2c-y := inv_mpu_i2c.o inv_mpu_acpi.o

obj-$(CONFIG_INV_MPU6050_SPI) += inv-mpu6050-spi.o

inv-mpu6050-spi-y := inv_mpu_spi.o

all:

make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

gzip -f inv-mpu6050-i2c.ko

gzip -f inv-mpu6050-spi.ko

gzip -f inv-mpu6050.ko

clean:

make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

rm inv-mpu6050-i2c.ko.gz

rm inv-mpu6050-spi.ko.gz

rm inv-mpu6050.ko.gz

Change to /root
cd /root
Create an device tree overlay source file for MPU9250:
nano /root/mpu9250.dts
Add the contents and save:

// Definitions for MPU9250
// Combination of:
// https://github.com/raspberrypi/linux/blob/rpi-4.9.y/arch/arm/boot/dts/overlays/mpu6050-overlay.dts
// and https://github.com/torvalds/linux/blob/master/Documentation/devicetree/bindings/iio/imu/inv_mpu6050.txt

// Driver codes:
// https://github.com/torvalds/linux/blob/master/drivers/iio/imu/inv_mpu6050/
// and
// https://github.com/torvalds/linux/tree/master/drivers/iio/magnetometer

/dts-v1/;
/plugin/;

/ {
compatible = "brcm,bcm2708";

fragment@0 {
target = <&i2c1>;
__overlay__ {
#address-cells = <1>;
#size-cells = <0>;
status = "okay";
clock-frequency = <400000>;

mpu9250: mpu9250@68 {
compatible = "invensense,mpu9250";
reg = <0x68>;
interrupt-parent = <&gpio>;
interrupts = <4 1>;
mount-matrix = "1", /* x0 */
"0", /* y0 */
"0", /* z0 */
"0", /* x1 */
"1", /* y1 */
"0", /* z1 */
"0", /* x2 */
"0", /* y2 */
"1"; /* z2 */

i2c-gate {
#address-cells = <1>;
#size-cells = <0>;
ak8963@c {
compatible = "asahi-kasei,ak8963";
reg = <0x0c>;
};
};
};
};
};

__overrides__ {
interrupt = <&mpu9250>,"interrupts:0";
};
};

Compile the device tree source and place it in overlays folder:
dtc -I dts -O dtb -o /boot/overlays/mpu9250.dtbo -b 0 -@ /root/mpu9250.dts
Update /boot/config.txt and add the following lines to it, save it and reboot:
dtoverlay=mpu9250
Read the Accelerometer and Magnetometer values like so:

[alarm@alarmpi ~]$ cat /sys/bus/iio/devices/iio\:device0/in_accel_x_raw

-794

[alarm@alarmpi ~]$ cat /sys/bus/iio/devices/iio\:device0/in_accel_y_raw

271

[alarm@alarmpi ~]$ cat /sys/bus/iio/devices/iio\:device0/in_accel_z_raw

16950

[alarm@alarmpi ~]$ cat /sys/bus/iio/devices/iio\:device1/in_magn_x_raw

[alarm@alarmpi ~]$ cat /sys/bus/iio/devices/iio\:device1/in_magn_y_raw

-14

[alarm@alarmpi ~]$ cat /sys/bus/iio/devices/iio\:device1/in_magn_z_raw

Python Bar Graph with Industrial I/O Driver

Install python packages (Latest versions from its git repository, replace the version number with latest one)

pacman -S libjpeg
python -m pip install git+https://github.com/peterbrittain/asciimatics.git@476159c95c5b6e34a782ea97503785ad95683805

Clone the git repository to fetch the example code

git clone https://github.com/peterbrittain/asciimatics.git

Then run following code using python for live bar graph:

from asciimatics.effects import Print

from asciimatics.renderers import BarChart, FigletText, SpeechBubble, Box

from asciimatics.scene import Scene

from asciimatics.screen import Screen

from asciimatics.exceptions import ResizeScreenError

import os

import sys

import math

import time

accel_x = open('/sys/bus/iio/devices/iio:device0/in_accel_x_raw', 'r')

accel_y = open('/sys/bus/iio/devices/iio:device0/in_accel_y_raw', 'r')

accel_z = open('/sys/bus/iio/devices/iio:device0/in_accel_z_raw', 'r')

gyro_x = open('/sys/bus/iio/devices/iio:device0/in_anglvel_x_raw', 'r')

gyro_y = open('/sys/bus/iio/devices/iio:device0/in_anglvel_y_raw', 'r')

gyro_z = open('/sys/bus/iio/devices/iio:device0/in_anglvel_z_raw', 'r')

mag_x = open('/sys/bus/iio/devices/iio:device1/in_magn_x_raw', 'r')

mag_y = open('/sys/bus/iio/devices/iio:device1/in_magn_y_raw', 'r')

mag_z = open('/sys/bus/iio/devices/iio:device1/in_magn_z_raw', 'r')

def _speak(screen, text, pos, start):

return Print(

screen,

SpeechBubble(text, None, uni=screen.unicode_aware),

x=pos[0] + 4, y=pos[1] - 4,

colour=Screen.COLOUR_WHITE,

clear=True,

start_frame=start,

stop_frame=start+50)

def accelx():

accel_x.seek(0)

accel = int(accel_x.readline())

accel = accel/16000 + 1

return accel if accel < 2 else 2

def accely():

accel_y.seek(0)

accel = int(accel_y.readline())

accel = accel/16000 + 1

return accel if accel < 2 else 2

def accelz():

accel_z.seek(0)

accel = int(accel_z.readline())

accel = accel/16000 + 1

return accel if accel < 2 else 2

def gyrox():

gyro_x.seek(0)

gyro = int(gyro_x.readline())

gyro = gyro/300 + 1

return gyro if gyro < 2 else 2

def gyroy():

gyro_y.seek(0)

gyro = int(gyro_y.readline())

gyro = gyro/300 + 1

return gyro if gyro < 2 else 2

def gyroz():

gyro_z.seek(0)

gyro = int(gyro_z.readline())

gyro = gyro/300 + 1

return gyro if gyro < 2 else 2

def magx():

mag_x.seek(0)

mag = int(mag_x.readline())

mag = mag/100 + 1

return mag if mag < 2 else 2

def magy():

mag_y.seek(0)

mag = int(mag_y.readline())

mag = mag/100 + 1

return mag if mag < 2 else 2

def magz():

mag_z.seek(0)

mag = int(mag_z.readline())

mag = mag/100 + 1

return mag if mag < 2 else 2

def demo(screen):

scenes = []

effects = [

Print(screen,

BarChart(

10, 40,

[accelx, accely, accelz],

colour=[c for c in range(1, 4)],

bg=[c for c in range(1, 4)],

scale=2.0,

axes=BarChart.X_AXIS,

intervals=0.5,

labels=True,

border=False),

x=0, y=0, transparent=False, speed=2),

_speak(screen, "Accelerometer", (0, 14), 0),

Print(screen,

BarChart(

10, 40,

[gyrox, gyroy, gyroz],

colour=[c for c in range(7, 10)],

bg=[c for c in range(7, 10)],

scale=2.0,

axes=BarChart.X_AXIS,

intervals=0.5,

labels=True,

border=False),

x=0, y=15, transparent=False, speed=2),

_speak(screen, "Gyroscope", (0, 29), 0),

Print(screen,

BarChart(

10, 40,

[magx, magy, magz],

colour=[c for c in range(4, 8)],

bg=[c for c in range(4, 8)],

scale=2.0,

axes=BarChart.X_AXIS,

intervals=0.5,

labels=True,

border=False),

x=44, y=0, transparent=False, speed=2),

_speak(screen, "Magnetometer", (50, 14), 0),

]

scenes.append(Scene(effects, -1))

screen.play(scenes, stop_on_resize=True)

while True:

try:

Screen.wrapper(demo)

sys.exit(0)

except ResizeScreenError:

pass

Try rotating the MPU9250 widget and watch the bars change.

Enable WiFi on your Raspberry Pi 3 Running Arch Linux ARM [Optional]

su root
sudo pacman -S netctl
nano /etc/netctl/wireless-home
Copy and paste the following contents and modify the SSID and passphrase to match your WiFi network

Description='A simple WPA encrypted wireless connection'

Interface=wlan0

Connection=wireless

Security=wpa

IP=dhcp

ESSID='MyNetwork'

# Prepend hexadecimal keys with \"

# If your key starts with ", write it as '""<key>"'

# See also: the section on special quoting rules in netctl.profile(5)

Key='WirelessKey'

# Uncomment this if your ssid is hidden

#Hidden=yes

# Set a priority for automatic profile selection

#Priority=10

netctl enable /etc/netctl/wireless-home
reboot

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