---
title: Xenomai
categories: embedded, arm, raspberrypi
...


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
===========

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？



實作
==================


Context switch

.. code-block:: prettyprint

    ksrc/arch/arm/switch.S
    /*
    /*
     * Switch context routine.
     *
     * Registers according to the ARM procedure call standard:
     *   Reg    Description
     *   r0-r3  argument/scratch registers
     *   r4-r9  variable register
     *   r10=sl stack limit/variable register
     *   r11=fp frame pointer/variable register
     *   r12=ip intra-procedure-call scratch register
     *   r13=sp stack pointer (auto preserved)
     *   r14=lr link register
     *   r15=pc program counter (auto preserved)
     *
     * Copied from __switch_to, arch/arm/kernel/entry-armv.S.
     * Right now it is identical, but who knows what the
     * future reserves us...
     *
     * XXX: All the following config options are NOT tested:
     *      CONFIG_IWMMXT
     *
     *  Calling args:
     * r0 = previous task_struct, r1 = previous thread_info, r2 = next thread_info
     */
    ENTRY(rthal_thread_switch)
            add     ip, r1, #TI_CPU_SAVE
     ARM(        stmia        ip!, {r4 - sl, fp, sp, lr} )        @ Store most regs on stack
     THUMB(        stmia        ip!, {r4 - sl, fp}           )        @ Store most regs on stack
     THUMB(        str        sp, [ip], #4                   )
     THUMB(        str        lr, [ip], #4                   )
            load_tls r2, r4, r5
    #ifdef USE_DOMAINS
        ldr     r6, [r2, #TI_CPU_DOMAIN]
    #endif
            clear_exclusive_monitor
            switch_tls r1, r4, r5, r3, r7
    #ifdef USE_DOMAINS
            mcr     p15, 0, r6, c3, c0, 0           @ Set domain register
    #endif
            fpu_switch r4
     ARM(        add        r4, r2, #TI_CPU_SAVE           )
     ARM(        ldmia        r4, {r4 - sl, fp, sp, pc}  )        @ Load all regs saved previously
     THUMB(        add        ip, r2, #TI_CPU_SAVE           )
     THUMB(        ldmia        ip!, {r4 - sl, fp}           )        @ Load all regs saved previously
     THUMB(        ldr        sp, [ip], #4                   )
     THUMB(        ldr        pc, [ip]                   )
    ENDPROC(rthal_thread_switch)

Timer
+++++++++++

Scheduler
+++++++++++
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

xnpod
+++++++++++

.. code-block:: prettyprint

    struct xnpod {

    xnflags_t status;	/*!< Status bitmask. */

    xnsched_t sched[XNARCH_NR_CPUS];	/*!< Per-cpu scheduler slots. */

    xnqueue_t threadq;	/*!< All existing threads. */
    #ifdef CONFIG_XENO_OPT_VFILE
    struct xnvfile_rev_tag threadlist_tag;
    #endif
    xnqueue_t tstartq,	/*!< Thread start hook queue. */
    tswitchq,		/*!< Thread switch hook queue. */
    tdeleteq;		/*!< Thread delete hook queue. */

    atomic_counter_t timerlck;	/*!< Timer lock depth.  */

    xntimer_t tslicer;	/*!< Time-slicing timer for aperiodic mode  */
    int tsliced;		/*!< Number of threads using the slicer */

    int refcnt;		/*!< Reference count.  */

    #ifdef __XENO_SIM__
    void (*schedhook) (xnthread_t *thread, xnflags_t mask);	/*!< Internal scheduling hook. */
    #endif	/* __XENO_SIM__ */
    };

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

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


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/`_