linux-mpu9150

An implementation of 9-axis data fusion on Linux using the InvenSense MPU-9150 IMU

The linux-mpu9150 code uses the InvenSense Embedded Motion Driver v5.1.1 SDK to obtain fused 6-axis quaternion data from the MPU-9150 DMP. The quaternion data is then further corrected in the linux-mpu0150 code with magnetometer data collected from the IMU.

Because it is primarily intended for use on small-board ARM computers, the linux-mpu9150 code uses 32-bit floats rather then doubles for all floating point operations.

Testing has been done with Raspberry Pi and Gumstix Overo and Duovero systems. The code should work fine with other small board systems like the BeagleBones.

We have our own boards incorporating the MPU9150s, but we also tested with the Sparkfun MPU9150 Breakout Boards

Fetch

Use git to fetch the linux-mpu9150 project. You may have to install git on your system first.

For RPi users running Raspbian, use this command

    sudo apt-get install git

Then to clone the repository assuming you have an Internet connection

    git clone https://github.com/Pansenti/linux-mpu9150.git

Build

The linux-mpu9150 code is written in C. There is a make file called Makefile-native for use when building directly on the system.

There is also a Makefile-cross makefile for use when using Yocto Project built tools and cross-building linux-mpu9150 on a workstation. This is more for Gumstix and Beagle users.

A recommendation is to create a soft-link to the make file you want to use.

    root@duovero:~$ cd linux-mpu9150
    root@duovero:~/linux-mpu9150$ ln -s Makefile-native Makefile

After that you can just type make to build the code.

    root@duovero:~/linux-mpu9150$ make
    gcc -Wall -DEMPL_TARGET_LINUX -DMPU9150 -DAK8975_SECONDARY -I eMPL -I glue -c eMPL/inv_mpu.c
    gcc -Wall -DEMPL_TARGET_LINUX -DMPU9150 -DAK8975_SECONDARY -I eMPL -I glue -c eMPL/inv_mpu_dmp_motion_driver.c
    gcc -Wall -DEMPL_TARGET_LINUX -DMPU9150 -DAK8975_SECONDARY -I eMPL -I glue -c glue/linux_glue.c
    gcc -Wall -DEMPL_TARGET_LINUX -DMPU9150 -DAK8975_SECONDARY -I eMPL -I glue -c mpu9150/mpu9150.c
    gcc -Wall -DEMPL_TARGET_LINUX -DMPU9150 -DAK8975_SECONDARY -c mpu9150/quaternion.c
    gcc -Wall -DEMPL_TARGET_LINUX -DMPU9150 -DAK8975_SECONDARY -c mpu9150/vector3d.c
    gcc -Wall -I eMPL -I glue -I mpu9150 -DEMPL_TARGET_LINUX -DMPU9150 -DAK8975_SECONDARY -c imu.c
    gcc -Wall inv_mpu.o inv_mpu_dmp_motion_driver.o linux_glue.o mpu9150.o quaternion.o vector3d.o imu.o -lm -o imu
    gcc -Wall -I eMPL -I glue -I mpu9150 -DEMPL_TARGET_LINUX -DMPU9150 -DAK8975_SECONDARY -c imucal.c
    gcc -Wall inv_mpu.o inv_mpu_dmp_motion_driver.o linux_glue.o mpu9150.o quaternion.o vector3d.o imucal.o -lm -o imucal

The result is two executables called imu and imucal.

For those using Makefile-cross, you will need to export an environment variable called OETMP that points to your OE temp directory (TMPDIR in build/conf/local.conf).

For example:

    scott@hex:~/linux-mpu9150$ export OETMP=/oe1
    scott@hex:~/linux-mpu9150$ ln -s Makefile-cross Makefile
    scott@hex:~/linux-mpu9150$ make
    /oe1/sysroots/`uname -m`-linux/usr/bin/armv7a-vfp-neon-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc -Wall -DEMPL_TARGET_LINUX -DMPU9150 -DAK8975_SECONDARY -I eMPL -I glue -c eMPL/inv_mpu.c
    /oe1/sysroots/`uname -m`-linux/usr/bin/armv7a-vfp-neon-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc -Wall -DEMPL_TARGET_LINUX -DMPU9150 -DAK8975_SECONDARY -I eMPL -I glue -c eMPL/inv_mpu_dmp_motion_driver.c
    /oe1/sysroots/`uname -m`-linux/usr/bin/armv7a-vfp-neon-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc -Wall -DEMPL_TARGET_LINUX -DMPU9150 -DAK8975_SECONDARY -I eMPL -I glue -c glue/linux_glue.c
    /oe1/sysroots/`uname -m`-linux/usr/bin/armv7a-vfp-neon-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc -Wall -DEMPL_TARGET_LINUX -DMPU9150 -DAK8975_SECONDARY -I eMPL -I glue -c mpu9150/mpu9150.c
    /oe1/sysroots/`uname -m`-linux/usr/bin/armv7a-vfp-neon-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc -Wall -DEMPL_TARGET_LINUX -DMPU9150 -DAK8975_SECONDARY -c mpu9150/quaternion.c
    /oe1/sysroots/`uname -m`-linux/usr/bin/armv7a-vfp-neon-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc -Wall -DEMPL_TARGET_LINUX -DMPU9150 -DAK8975_SECONDARY -c mpu9150/vector3d.c
    /oe1/sysroots/`uname -m`-linux/usr/bin/armv7a-vfp-neon-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc -Wall -I eMPL -I glue -I mpu9150 -DEMPL_TARGET_LINUX -DMPU9150 -DAK8975_SECONDARY -c imu.c
    /oe1/sysroots/`uname -m`-linux/usr/bin/armv7a-vfp-neon-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc -Wall inv_mpu.o inv_mpu_dmp_motion_driver.o linux_glue.o mpu9150.o quaternion.o vector3d.o imu.o -lm -o imu
    /oe1/sysroots/`uname -m`-linux/usr/bin/armv7a-vfp-neon-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc -Wall -I eMPL -I glue -I mpu9150 -DEMPL_TARGET_LINUX -DMPU9150 -DAK8975_SECONDARY -c imucal.c
    /oe1/sysroots/`uname -m`-linux/usr/bin/armv7a-vfp-neon-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc -Wall inv_mpu.o inv_mpu_dmp_motion_driver.o linux_glue.o mpu9150.o quaternion.o vector3d.o imucal.o -lm -o imucal

local_defaults.h

You can modify some default parameter settings in local_defaults.h to avoid having to pass command line switches to the applications every run.

After modifying local_defaults.h, you will have to run make again.

The defaults in local_defaults.h are for the RPi.

Enable i2c

Raspberry Pi

The RPi Raspbian distribution does not load the I2C kernel drivers by default.

You can check with this command:

    pi@raspberrypi:~/linux-mpu9150$ dmesg | grep i2c
    [   15.683106] i2c /dev entries driver
    [   15.767128] bcm2708_i2c bcm2708_i2c.0: BSC0 Controller at 0x20205000 (irq 79) (baudrate 100k)
    [   15.785938] bcm2708_i2c bcm2708_i2c.1: BSC1 Controller at 0x20804000 (irq 79) (baudrate 100k)

If you don't see output like the above, edit /etc/modules and add these lines

    i2c-bcm2708
    i2c-dev

The I2C device on the RPi P1 header will be /dev/i2c-1.

Gumstix

The I2C kernel driver for the Gumstix boards is usually loaded by default.

The I2C device on the Gumstix Overo expansion header is /dev/i2c-3.

On the Duovero the device it is /dev/i2c-2.

Any System

The permissions on the /dev/i2c-X device are usually set so that only the root user has permissions.

To avoid having to use sudo to run the code a udev rule can be used to change the permissions on startup.

Create a file:

    /etc/udev/rules.d/90-i2c.rules

and add the line:

    KERNEL=="i2c-[0-3]",MODE="0666"

Reboot to make sure everything is set correctly.

If you are running as root you don't need the udev rule.

Calibration

The IMU gyros have a built in calibration mechanism, but the accelerometers and the magnetometer require manual calibration.

Calibration, particularly magnetometer calibrations, is a complicated topic. We've provided a simple utility application called imucal that can get you started.

    pi@raspberrypi:~/linux-mpu9150$ ./imucal -h
     
    Usage: ./imucal <-a | -m> [options]
      -b <i2c-bus>          The I2C bus number where the IMU is. The default is 1 for /dev/i2c-1.
      -s <sample-rate>      The IMU sample rate in Hz. Range 2-50, default 10.
      -a                    Accelerometer calibration
      -m                    Magnetometer calibration
                            Accel and mag modes are mutually exclusive, but one must be chosen.
      -f <cal-file>         Where to save the calibration file. Default ./<mode>cal.txt
      -h                    Show this help
    
    Example: ./imucal -b3 -s20 -a

You'll need to run this utility twice, once for the accelerometers and again for the magnetometer.

Here is how to generate accelerometer calibration data on an RPi. The default bus and sample rate are used.

    pi@raspberrypi:~/linux-mpu9150$ ./imucal -a
    
    Initializing IMU .......... done
    
    
    Entering read loop (ctrl-c to exit)
    
    X -16368|16858|16858    Y -16722|-2490|16644    Z -17362|-562|17524             ^C

The numbers shown are min|current|max for each of the axes.

What you want to do is slowly move the RPi/imu through all orientations in three dimensions. Slow is the the key. We are trying to measure gravity only and sudden movements will induce unwanted accelerations.

The values will update whenever there is a change in one of the min/max values, so when you see no more changes you can enter ctrl-c to exit the program.

When it finishes, the program will create an accelcal.txt file recording the min/max values.

    pi@raspberrypi:~/linux-mpu9150$ cat accelcal.txt 
    -16368
    16858
    -16722
    16644
    -17362
    17524

Do the same thing for the magnetometers running imucal with the -m switch.

    pi@raspberrypi:~/linux-mpu9150$ ./imucal -m
    
    Initializing IMU .......... done
    
    
    Entering read loop (ctrl-c to exit)
    
    X -179|-54|121    Y -154|199|199    Z -331|-124|15             ^C

Again move the device through different orientations in all three dimensions until you stop seeing changes. You can move faster during this calibration since we aren't looking at accelerations.

After ending the program with ctrl-c, a calibration file called magcal.txt will be written.

    pi@raspberrypi:~/linux-mpu9150$ cat magcal.txt 
    -179
    121
    -154
    199
    -331
    15

If these two files, accelcal.txt and magcal.txt, are left in the same directory as the imu program, they will be used by default.

Run

The imu application is a small example to get started using linux-mpu9150 code.

    pi@raspberrypi ~/linux-mpu9150 $ ./imu -h

    Usage: ./imu [options]
      -b <i2c-bus>          The I2C bus number where the IMU is. The default is 1 to use /dev/i2c-1.
      -s <sample-rate>      The IMU sample rate in Hz. Range 2-50, default 10.
      -y <yaw-mix-factor>   Effect of mag yaw on fused yaw data.
                            0 = gyro only
                            1 = mag only
                            > 1 scaled mag adjustment of gyro data
                            The default is 4.
      -a <accelcal file>    Path to accelerometer calibration file. Default is ./accelcal.txt
      -m <magcal file>      Path to mag calibration file. Default is ./magcal.txt
      -v                    Verbose messages
      -h                    Show this help

    Example: ./imu -b3 -s20 -y10

The defaults will work for an RPi with the two calibration files picked up automatically.

    pi@raspberrypi ~/linux-mpu9150 $ ./imu

    Initializing IMU .......... done


    Entering read loop (ctrl-c to exit)

     X: -2 Y: -62 Z: -4        ^C

The default output of the imu program are the fused Euler angles. Other outputs are available such as the fused quaternion and the raw gyro, accel and mag values. See the source code.

Keep in mind imu is just a demo app not optimized for any particular use. The idea is that you'll write your own program to replace imu.

All of the functions in the Invensense SDK under the eMPL directory are available. See mpu9150/mpu9150.c for some examples.