版本 79d9635563657b6f2221a450e1b1e32bd13c3d4e
Xenomai
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
Real Time 定義
作業系統架構
.. image:: /xenoarch2.jpg
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__ */
};
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/
_