Real-Time Kernel for RaspberryPi 2

This post will describe how to compile a RT-kernel for RaspberryPi 2.

I'm using UBUNTU 14.04 LTS 64bit for compiling Raspbian Jessie.

After a long time, I needed a RT kernel for a new project with the new RaspberryPi2. Realizing My old post has broken links, I struggled again with the task. This time, after a successful attempt, I'm determined to put it all here step by step.

following:

https://github.com/emlid/linux-rt-rpi

https://www.raspberrypi.org/documentation/linux/kernel/building.md and https://www.raspberrypi.org/documentation/linux/kernel/configuring.md and http://wiki.linuxcnc.org/cgi-bin/wiki.pl?RaspbianXenomaiBuild#Post_install

##### Tested on UBUNTU 14.04 LTS with Rasbian Jessie 4.1

# install needed packages for compiling the kernel

sudo apt-get install libncurses5-dev libncursesw5-dev

#Download Raspberry Pi tools:

git clone https://github.com/raspberrypi/tools.git

# Download source files and patches

git clone -b rpi-4.1.y --depth 1 git://github.com/raspberrypi/linux.git linux-rpi-4.1.y

# Download RT patch 

wget https://www.kernel.org/pub/linux/kernel/projects/rt/4.1/patch-4.1.15-rt17.patch.xz

xz -d patch-4.1.15-rt17.patch.xz

# patch the kernel. This step might produce errors

# if rt-patch and the kernel don't match

cd linux-rpi-4.1.y

cat ../patch-4.1.15-rt17.patch | patch -p1

#Export the following variables to specify cross-compilation options:

export ARCH=arm 

#to compile on a x64-machine you need to export:

export CROSS_COMPILE=~/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/bin/arm-linux-gnueabihf-

#create a config file for Raspberry Pi 2:

make CROSS_COMPILE=${CROSS_COMPILE} ARCH=arm bcm2709_defconfig

# make changes to the config

make CROSS_COMPILE=${CROSS_COMPILE} ARCH=arm menuconfig

enable Preemption model -> Fully preemptible Kernel (RT)

change timer freq to 1000Hz

enable device tree (all options)

#Compile the kernel:

make CROSS_COMPILE=${CROSS_COMPILE} ARCH=arm -j5

#Install modules, will result in "lib" folder with modules and firmware:

mkdir kernel-rt

INSTALL_MOD_PATH=kernel-rt make CROSS_COMPILE=${CROSS_COMPILE} ARCH=arm modules_install

## Install the kernel to non-RT image:

Copy arch/arm/boot/Image to /boot/kernel7.img on SD card.

Copy arch/arm/boot/dts/bcm2709-rpi-2-b.dtb to /boot/bcm2709-rpi-2-b.dtb on SD card

# add to /boot/config.txt

echo “device_tree=bcm2709-rpi-2-b.dtb” >> /boot/config.txt

Copy (merge if necessary) kernel-rt/lib to / on SD card.

## Testing RT-Image

Insert SD card and connect RPI to power, keyboard and screen. 

Login with user pi and password raspberry

#Installing cyclictest utility on Raspberry Pi:

git clone http://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git 

cd rt-tests

make all

cp ./cyclictest /usr/bin/

cd ~

sudo cyclictest -l100000 -m -n -a0 -t1 -p99 -i400 -h400 -q

# WITH NO RT RESULT:

# Total: 000100000

# Min Latencies: 00015

# Avg Latencies: 00021

# Max Latencies: 00118

# Histogram Overflows: 00000

# Histogram Overflow at cycle number:

# Thread 0:

# WITH RT RESULT:

# Total: 000100000

# Min Latencies: 00013

# Avg Latencies: 00020

# Max Latencies: 00066

# Histogram Overflows: 00000

# Histogram Overflow at cycle number:

# Thread 0:

Real-Time Kernel for RaspberryPi (Take II)

After unsuccessful attempt to compile Archlinux-rt kernel,
I encountered a very good guide describing how to compile a Debian Linux-rt kernel with Xenomai for the RaspberryPi. and a completing page for creating the RPI image.
I can't say I understand it completely, but I managed to combine to two guides and compile my own RaspberryPi Linux-rt kernel.

I'm sure some of the steps are missing and things change very quickly (e.g. links, kernel versions and patches) so anyone following my steps should take that into consideration and adapt to changes.

I started by installing a fresh Debian 32bit x86 on a virtual box.
Follow the picnc guides but remember to adapt the patches and kernel version differences.

I'll try to redo the process and give here a complete guide at a later stage.

Machinoid Real-Time Linux for RaspberryPi

Download and install Machinoid following: http://www.machinoid.com/?p=10
apt-get install libtool gfortran
apt-get install libusb-1.0
install xenomai following the instructions in the link above.
sysctl vm.min_free_kbytes=8192
vi /etc/ld.so.conf.d/xenomai.conf
add 2 lines:
  # xenomai default configuration
  /usr/xenomai/lib
ldconfig
install wifi drivers (after I got problems with rt2800usb driver):
apt-get install firmware-ralink

create new file /etc/modprobe.d/8192cu.conf
add:
# Disable power saving
options 8192cu rtw_power_mgnt=0 rtw_enusbss=1 rtw_ips_mode=1

in /etc/dhcp/dhcp.conf

uncomment the timeout line and edit:

timeout 100;

LSM303 accelerometer on RaspberryPi

After getting my new LSM303 accelerometer, I got my great electronics tec. Daviv Shtibelman to wire it up for RPI.
Connecting LSM303 pins 1 (SCL), 2 (SDA), 6 (GND) and 8 (V3V) to pins 5 (SCL), 3 (SDA), 6 (GND) and 1 (V3V) on the Pi board.
On my ArchlinuxARM OS I had to install i2c-tools:
> pacman -S i2c-tools
And add i2c modules:
> echo i2c-dev > /etc/modules-load.d/ i2c.conf
> echo i2c-bcm2708 >> /etc/modules-load.d/ i2c.conf
> reboot

now to check it works:
> i2cdetect -y 1
got a message like this:
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- 19 -- -- -- -- 1e --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

Now, following this, I test it and it works. Now I'm up for creating my own code.

Made some changes to the code:

main.cpp

#include"LSM303DLHC.h"
#include<stdio.h>
#include <unistd.h>


/*
   getHeading() calculates a tilt-compensated heading.
   A float between 0 and 360 degrees is returned. You need
   to pass this function both a magneto and acceleration array.
 
   Headings are calculated as specified in AN3192:
   http://www.sparkfun.com/datasheets/Sensors/Magneto/Tilt%20Compensated%20Compass.pdf
 
*/

float getHeading(LSM303& lsm303dlhc);

#define PI 3.141592654


int main(void)
{
    uint8_t bajt;
    const char *fileN = "/dev/i2c-1";
    LSM303 lsm303dlhc(fileN);

    lsm303dlhc.enalbe();

    while(1)
    {
        lsm303dlhc.readAccelerationRaw();
        lsm303dlhc.readMagnetometerRaw();
        printf("acc [m/s^2]: \e[27;1;31m %f \e[m \e[27;1;32m %f \e[m \e[27;1;34m %f \e[m mag:  \e[27;1;31m %d \e[m  \e[27;1;32m %d \e[m \e[27;1;34m %d\e[m %fdeg\n",
               (int16_t)lsm303dlhc.acc_x_raw*0.00957,(int16_t)lsm303dlhc.acc_y_raw*0.00957,-(int16_t)lsm303dlhc.acc_z_raw*0.00957,
               (int16_t)lsm303dlhc.mag_x_raw, (int16_t)lsm303dlhc.mag_y_raw, (int16_t)lsm303dlhc.mag_z_raw,getHeading(lsm303dlhc));
        usleep(10);
       }

    }


float getHeading(LSM303& lsm303dlhc)
{
  float heading,pitch,roll,xh,yh,zh;
  // see section 1.2 in app note AN3192
  int magValue[3];
  float accelValue[3];
  magValue[0] = (int16_t)lsm303dlhc.mag_x_raw;
  magValue[1] = (int16_t)lsm303dlhc.mag_y_raw;
  magValue[2] = (int16_t)lsm303dlhc.mag_z_raw;
  accelValue[0] = (int16_t)lsm303dlhc.acc_x_raw*0.000976531;
  accelValue[1] = (int16_t)lsm303dlhc.acc_y_raw*0.000976531;
  accelValue[2] = -(int16_t)lsm303dlhc.acc_z_raw*0.000976531;

    // see appendix A in app note AN3192
  pitch = asin(-accelValue[0]);
  roll = asin(accelValue[1]/cos(pitch));

  xh = magValue[0] * cos(pitch) + magValue[2] * sin(pitch);
  yh = magValue[0] * sin(roll) * sin(pitch) + magValue[1] * cos(roll) - magValue[2] * sin(roll) * cos(pitch);
  zh = -magValue[0] * cos(roll) * sin(pitch) + magValue[1] * sin(roll) + magValue[2] * cos(roll) * cos(pitch);

  heading = 180*atan2(yh,xh)/PI;

  if (heading <0)
    heading += 360;

  return heading;
}

LSM303DLHC.cpp:

#include"LSM303DLHC.h"
#include<math.h>
#include<stdio.h>

/*Conection to Raspberry PI:
 LSM303     Raspberry PI
 VDD    ->  3V3(PIN 1)
 SDA    ->  SDA(PIN 3)
 SCL    ->  SCL(PIN 5)
 GND    ->  GND(PIN 6)
*/

#define LSM303DLHC_MAG_ADDRESS            (0x3C >> 1)
#define LSM303DLHC_ACC_ADDRESS            (0x32 >> 1)

LSM303::LSM303(const char * i2cDeviceName) : i2c_lsm303(i2cDeviceName)
{

}

uint8_t LSM303::readAccRegister(uint8_t regAddr)
{
    i2c_lsm303.addrSet(LSM303DLHC_ACC_ADDRESS);
    return i2c_lsm303.readByte(regAddr);
}

uint8_t LSM303::readMagRegister(uint8_t regAddr)
{
    i2c_lsm303.addrSet(LSM303DLHC_MAG_ADDRESS);
    return i2c_lsm303.readByte(regAddr);
}

void LSM303::writeAccRegister(uint8_t regAddr,uint8_t byte)
{
    i2c_lsm303.addrSet(LSM303DLHC_ACC_ADDRESS);
    i2c_lsm303.writeByte(regAddr, byte);

}

void LSM303::writeMagRegister(uint8_t regAddr, uint8_t byte)
{
    i2c_lsm303.addrSet(LSM303DLHC_MAG_ADDRESS);
    i2c_lsm303.writeByte(regAddr, byte);

}

void LSM303::enalbe(void)
{
   writeAccRegister(LSM303_CTRL_REG1, 0b10010111);
   writeAccRegister(LSM303_CTRL_REG4, 0b00001000);

   writeMagRegister(LSM303_MR_REG, 0x00);
}

void LSM303::readAccelerationRaw(void)
{
    uint8_t block[6];

    i2c_lsm303.addrSet(LSM303DLHC_ACC_ADDRESS);

    i2c_lsm303.readBlock(0x80 | LSM303_OUT_X_L_A, sizeof(block), block);
    acc_x_raw = (int16_t)(block[0] | (block[1] << 8)) >> 4;
    acc_y_raw = (int16_t)(block[2] | block[3] << 8) >> 4;
    acc_z_raw = (int16_t)(block[4] | block[5] << 8) >> 4;

}

void LSM303::readMagnetometerRaw(void)
{
    uint8_t block[6];

    i2c_lsm303.addrSet(LSM303DLHC_MAG_ADDRESS);
    i2c_lsm303.readBlock(0x80 | LSM303_OUT_X_H_M, sizeof(block), block);

    mag_x_raw = (int16_t)(block[1] | block[0] << 8);
    mag_y_raw = (int16_t)(block[5] | block[4] << 8);
    mag_z_raw = (int16_t)(block[3] | block[2] << 8);

}

void LSM303::readAcceleration(void)
{
    readAccelerationRaw();
}

Real-Time Kernel for RaspberryPi

After installing and running ArchLinuxARM on my RaspberryPi, I tried to compile a real-time kernel.
With the help of moonman, following this ArchLinuxARM forum thread, I downloaded the RT patch:
https://www.kernel.org/pub/linux/kernel/projects/rt/3.6/patch-3.6.11.4-rt36.patch.gz
and the PKGBUILD:
# git clone https://github.com/archlinuxarm/PKGBUILDs.git
following this, I updated pacman:
# pacman -Syy
and installed some packages:
# pacman -S kernel26-headers file base-devel abs
next
# cd PKGBUILDs/core/linux-raspberrypi
and edit the PKGBUILD file to include the patch in the source array:

source=('config'
        'change-default-console-loglevel.patch'
        'usb-add-reset-resume-quirk-for-several-webcams.patch'
        'args-uncompressed.txt'
        'boot-uncompressed.txt'
        'imagetool-uncompressed.py'
        'https://raspy-juice.googlecode.com/svn/trunk/linux-rtc/0001-rtc-pcf8523.patch'
        'https://raspy-juice.googlecode.com/svn/trunk/linux-rtc/0002-pcf8523-i2c-register-dt.patch'
        'patch-3.6.11.4-rt36.patch')

add a patch line:

patch -Np1 -i "${srcdir}/patch-3.6.11.4-rt36.patch"

and add md5sums at the end of the PKGBUILD file. to get the correct number run:

# md5sum patch-3.6.11.4-rt36.patch

next for the build:

# makepkg --asroot -Acs

The process has failed with some rejections of patches. So we need to manually apply the patches:

first look for rejections:

# find . -name "*.rej"

then edit the file and the .rej file:

# vim XXX.c XXX.c.rej

replacing XXX with the file path and name.

Then use :split to split the screen :next to change one screen to .rej file and ctrl+ww to switch between files.

add the lines marked by + and remove lines marked by - (lines with no +- sign are used for orientation.

after manually patching all files, edit the PKGBUILD file to ignore the kernel git and the patches (adding # at the start of the line)
add a line to src/linux/security/apparmor/sid.c:
"#include <linux/cache.h>"

re-run:

# makepkg --asroot

Now for the installation part:
# pacman -U linux-headers-raspberrypi-3.6.11-11-armv6h.pkg.tar.xz linux-raspberrypi-3.6.11-11-armv6h.pkg.tar.xz

And reboot.

Well, it didn't work.

RaspberryPi initial steps

I initiated a new project involving low-cost micro-computer RaspberryPi.
In order to begin I ordered some basic parts (costs are in USD for Israeli market, should be cheaper elsewhere):
a RaspberryPi (55$)
5v charger with microusb adapter (10$)
8GB SD card (12$)
HDMI cable (8$)

and some extra parts:
3.5" LCD screen (45$)
micro-keyboard (62$)
micro-sd low profile adapter (11.9$)
wifi dongle (18.6$)

Not so cheap but might be worth it.

after I got a couple of RaspberryPi (model B rev2 512MB RAM) devices for a project I'm working on (details about the project will come later if it will work).
I bought a SD 8GB card and hooked it to the my desktop computer.
I downloaded the ARCLinux image unzipped it and followed the instructions:

Replacing sdX with the location of the SD card, run:
dd bs=1M if=/path/to/archlinux-hf-2013-06-15.img of=/dev/sdX

In order to increase the SD space to it's full 8GB I used gparted.

upgrade system:
> pacman -Sy pacman
> pacman-key --init
> pacman -Syu
sync (3 times):
# sync
reboot:
# reboot
Now I can add packages using pacman. to look for a package use:
> pacman -Ss <package name>
then select the one you need and install by:
> pacman -S <package name>

I am currently testing the Pi with the screen and 8 AA batteries to see how long it can work. I plan to build a case with a built-in 3.5" screen and a miniature keyboard so I can have a control unit for other RaspberryPi devices. My initial thoughts of using an old Gamboy case are now switched (with the encouragement of my electronic tec. guy David Shtibelman) to build a costume made case. Of course, David is the one to build it, since I have no skills to do that.