kernel build & preempt-rt patch & xenomai

提前准备好 linux 内核源代码，假设是 x86 系统。能够去下载原生内核（Vanilla kernel）：
wget https://www.kernel.org/pub/linux/kernel/v3.x/linux-3.18.17.tar.gz

假设是arm系统，或者其它系统，则下载厂商定制过的内核源代码。

假设有须要。patch内核。如 preempt-rt 补丁：（注意补丁版本号必须与内核版本号相应，此处均为 3.18.17 版本号。假设是定制过的内核。则必须找到相应定制过的补丁.）

wget https://www.kernel.org/pub/linux/kernel/projects/rt/3.18/patch-3.18.17-rt14.patch.gz   // 注意 patch 和 patchs

cd linux-3.18.17    //内核源代码根文件夹
zcat ../patch-3.18.17-rt14.patch.gz | patch -p1     // 打补丁，假设.bz2压缩格式则使用 bzcat；
// 假设在源代码根文件夹的上层文件夹。则 patch -p0 < xxx.patch

在现有系统上改动配置：

make mrproper   //清理一下
scp pi@raspberrypi:/proc/config.gz .    //复制现有系统的配置文件，x86系统则能够找到 /boot/config-3.18.17-32-generic 文件

gunzip -c config.gz > .config

// 由于你的交叉编译器可能不叫gcc。而是 arm-linux-gnueabihf-gcc，所以：
export CCPREFIX=/home/raspberry/tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian/bin/arm-linux-gnueabihf-
// 这样子执行你的交叉编译器：
${CCPREFIX}gcc -v

//依据须要改动.config文件，或者 make menuconfig 图形化改动内核配置
ARCH=arm CROSS_COMPILE=${CCPREFIX} make menuconfig

ARCH=arm CROSS_COMPILE=${CCPREFIX} make -jx        // build kernel, 多核系统

mkdir module_build_directory
INSTALL_MOD_PATH=module_build_directory make modules_install  // build modules
// 这里是交叉编译。所以不能直接安装。假设是x86系统，直接 make && sudo make modules_install && sudo make install && sudo update-grub 就可以

复制新的内核到sd卡（树莓派2）

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

cd linux/arch/arm/boot
scp Image pi@raspberrypi:/tmp
scp dtb/bcm2709-rpi-2-b.dtb pi@raspberrypi:/tmp

cd module_build_directory
tar czf modules.tgz *
scp modules.tgz pi@raspberrypi:/tmp

// ssh to raspberry
ssh pi@your_ip_address_to_rasp
cd /
sudo mv /tmp/Image /boot/kernel7.img        // 忽略属性不同的信息
scp mv /tmp/bcm2709-rpi-2-b.dtb /boot/bcm2709-rpi-2-b.dtb   
sudo tar xzf /tmp/modules.tgz           // 解压后能够通过ls /lib/modules查看

关于内核配置

Symbol(s) Description：
[ ], [*]    Options in square brackets can be activated or deactivated. The asterisk marks the menu entry as activated. The value can be changed with the space key. It is also possible to press Y key (Yes) to activate or N key (No) to deactivate the selected entry.

If the option is activated, the selected feature/driver will be built into the kernel and will always be available at boot time.

< >, <M>, <*>   Options in angle brackets can be activated or deactivated, but also activated as module (indicated by a M). The values can be modified by pressing Y/N keys as before or by pressing the M key to activate the feature/driver as a module.

See the Kernel Modules article for differentiation.

{M}, {*}    Options in curly brackets can be activated or activated as module but not be deactivated. This happens because another feature/driver is dependent on this feature.
-M-, -*-    Options between hyphens are activated in the shown way by another feature/driver. There is no choice.

Tag Description:
(NEW)   This driver is new in the kernel and is maybe not stable enough.
(EXPERIMENTAL)  This driver is experimental and most likely not stable enough.
(DEPRECATED)    This driver is deprecated and not needed for most systems.
(OBSOLETE)  This driver is obsolete and should not be activated.

关于 x86 的 preemt-rt patch & kernel build，见连接：

https://ubuntuforums.org/showthread.php?
t=2273355
http://askubuntu.com/questions/72964/how-can-i-install-a-realtime-kernel
https://sourceforge.net/p/emc/mailman/message/33665819/ 这个注意是使用 64 位系统还是 32位。可能须要改动 .config 文件。

假设有哪个 kernel config 不懂的话。能够在这个里头搜:

https://cateee.net/lkddb/

preempt-rt kernel config:

CONFIG_PREEMPT_RT_FULL: Kernel Features > Preemption Model > Fully Preemptible Kernel (RT)
Enable HIGH_RES_TIMERS: General Setup > Timers subsystem > High Resolution Timer Support (already enabled)

去掉某些 ACPI 和 PowerManage 相关选项，不能所有去掉，由于高精度时钟可能会依赖当中某些配置
去掉 CPU 频率调整选项等
去掉 Device Driver 中的 Staging Drivers 选项
去掉 Kernel Hacking 中的某些 debug 选项（假设不须要debug内核的话）

推荐配置例如以下（xenomai-2.6.5）：

 * General setup
  --> Local version - append to kernel release: -xenomai-2.6.5
  --> Timers subsystem
      --> High Resolution Timer Support (Enable)
 * Real-time sub-system
  --> Xenomai (Enable)
  --> Nucleus (Enable)
 * Power management and ACPI options
  --> Run-time PM core functionality (Disable)
  --> ACPI (Advanced Configuration and Power Interface) Support
      --> Processor (Disable)
  --> CPU Frequency scaling
      --> CPU Frequency scaling (Disable)
  --> CPU idle
      --> CPU idle PM support (Disable)
 * Pocessor type and features
  --> Processor family
      --> Core 2/newer Xeon (if "cat /proc/cpuinfo | grep family" returns 6, set as Generic otherwise)
 * Power management and ACPI options
  --> Memory power savings
      --> Intel chipset idle memory power saving driver

假设遇到问题，查看 linux log ( dmesg | grep -i xenomai )，查找相应问题 see link: http://www.xenomai.org/documentation/xenomai-head/TROUBLESHOOTING.txt
假设是 xeno latency 測试，发现 周期性高延时，那么非常可能是遇到了 SMI 的问题。

About how to fix it:

kernel build &amp; preempt-rt patch &amp; xenomai

preempt-rt kernel config:

kernel build & preempt-rt patch & xenomai