Xenomai

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=/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

Xenomai是一個linux kernel的patch 藉由在底層增加一個架構 負責硬體與接收interrupt 並將interrupt 傳給上層的OS(這邊稱為domain)

這個底層的架構是Adeos 是另一個open source的project

基本架構示意圖 http://dchabal.developpez.com/tutoriels/linux/xenomai/images/image04.png 在api呼叫上可以看到不同層級的抽象化 ipipe_XXX -> rthal_XXX -> xnXXX 上一層對下一層的操作方式基本上會固定 但下一層的實作一硬體或config有所差異

負責傳送interrupt的程式稱為ipipe 示意圖 http://www.xenomai.org/documentation/xenomai-2.6/html/pictures/life-with-adeos-img4.jpg 可以找到ipipe_raise_irq()將interrupt推到pipeline

在ipipe上每個domain都有自己的優先度 高優先度的domain會先接收到interrupt 高優先度的domain的thread 可以preempt 低優先度domain的thread

• 與 RT-PREEMPT 途徑的差異？

依據預設 Xenomai 組態，nucleus 程式碼的兩個檔案未被編譯進去： - sched-tp.c - sched-sporadic.c

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/_