---
title: Xenomai
categories: embedded, arm, raspberrypi
toc: no
...

組員
----
* 向澐
* 林家宏
* 呂科進
* 趙愷文
* 阮志偉
* 陳建霖

Building an RPi Xenomai Kernel
------------------------------
* Install Cross complier

.. code-block:: c

    cd <working dir>
    wget https://github.com/raspberrypi/tools/archive/master.tar.gz
    tar xzf master.tar.gz

* Download source files and patches
  - Download kernel

  .. code-block:: c

      git clone -b rpi-3.8.y --depth 1 git://github.com/raspberrypi/linux.git linux-rpi-3.8.y
  - Download Xenomai 

  .. code-block:: c

      git clone git://git.xenomai.org/xenomai-head.git xenomai-head
  - Download minimal config 

  .. code-block:: c

      wget https://www.dropbox.com/s/dcju74md5sz45at/rpi_xenomai_config

* Apply patches

  - Apply ipipe core pre-patch

  .. code-block:: c

    cd linux-rpi-3.8.y
    patch -Np1 < ../xenomai-head/ksrc/arch/arm/patches/raspberry/ipipe-core-3.8.13-raspberry-pre-2.patch

  - Apply Xenomai ipipe core patch 

  .. code-block:: c

    xenomai-head/scripts/prepare-kernel.sh --arch=arm --linux=linux-rpi-3.8.y --adeos=xenomai-head/ksrc/arch/arm/patches/ipipe-core-3.8.13-arm-3.patch

  - Apply ipipe core post-patch 

  .. code-block:: c

    cd linux-rpi-3.8.y
    patch -Np1 < ../xenomai-head/ksrc/arch/arm/patches/raspberry/ipipe-core-3.8.13-raspberry-post-2.patch

* Compile kernel

  - Create build directory 

  .. code-block:: c

    mkdir linux-rpi-3.8.y/build

  - Configure kernel

  .. code-block:: c

    cp rpi_xenomai_config linux-rpi-3.8.y/build/.config
    cd linux-rpi-3.8.y
    make mrproper
    make ARCH=arm O=build oldconfig

  - Compile 

  .. code-block:: c

    make ARCH=arm O=build CROSS_COMPILE=../../tools-master/arm-bcm2708/arm-bcm2708hardfp-linux-gnueabi/bin/arm-bcm2708hardfp-linux-gnueabi-
   
  - Install modules

  .. code-block:: c

    make ARCH=arm O=build INSTALL_MOD_PATH=dist modules_install

  - Install headers

  .. code-block:: c

    make ARCH=arm O=build INSTALL_HDR_PATH=dist headers_install
    find build/dist/include \( -name .install -o -name ..install.cmd \) -delete

* 編譯好的kernelImage,移到SD卡的 ``/boot/`` 路徑下並更改名稱為kernel.img
* 將``linux-rpi-3.8.y/build/dist``中的Module,移到SD卡中的``/lib/modules``
* Cyclictest
  - Linux

  .. code-block:: c
    

  - Xenomai

  .. code-block:: c
    
    cd xenomai-head
    export PATH=<your path>/tools-master/arm-bcm2708/arm-bcm2708hardfp-linux-gnueabi/bin/:$PATH
    ./configure --host=arm-bcm2708hardfp-linux-gnueabi
    cd src
    mkdir dist
    make install DIST_DIR=dist

  dist中會出現``usr/xenomai``
  將這個資料夾移到sd卡中 ``/usr/``

  在raspberry pi中

  .. code-block:: c

    export PATH=/usr/xenomai/bin:$PATH  
    export LD_LIBRARY_PATH=/usr/xenomai/lib
    sudo modprobe xeno_posix

   接著就能跑使用xenomai機制的cyclictest

  - RT_preempt


作業系統架構
------------
* 與 RT-PREEMPT 途徑的差異？

nucleus 編出來的.o檔中關於sched的有
    - xenomai/nucleus/sched-rt.o
    - xenomai/nucleus/sched-idle.o
    - xenomai/nucleus/sched.o

因此在nucleus source code中
    - sched-tp.c
    - sched-sporadic.c
這兩個應該是沒被用到

硬體驅動原理
------------
* 硬體使用 Raspberry Pi

效能表現
--------
* `Cyclictest<https://rt.wiki.kernel.org/index.php/Cyclictest>`_
* Test case: POSIX interval timer, Interval 500 micro seconds,. 100000 loops, 100% load.
  - Commandline: cyclictest -t1 -p 80 -i 500 -l 100000

* 使用 PREEMPT LINUX

.. code-block:: prettyprint

    root@raspberrypi:/home/pi# sudo ./cyclictest -t1 -p 80 -i 500 -l 100000
    # /dev/cpu_dma_latency set to 0us
    policy: fifo: loadavg: 0.00 0.01 0.05 1/61 2064          
    T: 0 ( 2063) P:80 I:500 C: 100000 Min:     27 Act:   49 Avg:   42 Max:    1060

* 使用 RT-PREEMPT

.. code-block:: prettyprint

    Linux raspberrypi 3.6.11+ #474 PREEMPT Thu Jun 13 17:14:42 BST 2013 armv6l GNU/Linux
    Min:     22 Act:   31 Avg:   32 Max:     169

* 使用 Xenomai

.. code-block:: prettyprint

    Linux raspberrypi 3.8.13-core+ #1 Thu Feb 27 03:02:16 CST 2014 armv6l GNU/Linux
    Min:      1 Act:    5 Avg:    6 Max:      41

.. code-block:: prettyprint

    root@raspberrypi:/home/pi# /usr/xenomai/bin/cyclictest -t1 -p 80 -i 500 -l 10000 
    0.08 0.06 0.05 1/61 2060          
    T: 0 ( 2060) P:80 I:     500 C:  100000 Min:      -4 Act:      -2 Avg:       0 Max:      30

* cyclictest 做法

概念:
    取得現在時間接著讓process睡一個間隔
    等process醒來後再取一次時間
    比對兩次取得的時間差與設定的間隔差距

pseudocode:

.. code-block:: prettyprint

    clock_gettime((&now))
    next = now + par->interval
    while (!shutdown) {
        clock_nanosleep((&next))
        clock_gettime((&now))
        diff = calcdiff(now, next)
        # update stat-> min, max, total latency, cycles
        # update the histogram data
        next += interval
    }

造成這時間差的可能原因:

    timer精準度

    interrupt latency

    interrupt handler duration

    scheduler latency

    scheduler duration

    context switch

討論用
--------
https://embedded2014.hackpad.com/Xenomai-raspberry-note-XwJtuQn9nkD

參考資料
--------
* https://code.google.com/p/picnc/wiki/RPiXenomaiKernel
* https://code.google.com/p/picnc/wiki/CreateRaspbianLinuxCNC
* http://www.camelsoftware.com/firetail/blog/raspberry-pi/real-time-operating-systems/
* `Quadruped Linux robot feels its way over obstacles<http://linuxgizmos.com/hyq-quadruped-robot-runs-real-time-linux/>`_
* ` Choosing between Xenomai and Linux for real-time applications<https://www.osadl.org/fileadmin/dam/rtlws/12/Brown.pdf>`_
* `Real Time Systems<http://www.slideshare.net/anil_pugalia/real-time-systems>`_
* `http://www.cs.ru.nl/lab/xenomai/exercises/`_