[[labs.beatcraft.com]]~
[[Raspberry Pi]]~
[[Raspbian]]~
#contents

*Raspberry Pi 2 kernel self-compile [#y849a1c8]
>
This is a process to compile the kernel on Raspberry 2, which is currently working on a Raspberry Pi.~
~
To create Linux environment for ARM architecture, a x86/x86_64 based cross-compile host environment is often used since its speed of compiling. Recently, since faster ARM machines such as Raspberry Pi 2 have been developed, self-compiling on ARM is a reasonable alternative to cross-compiling on x86/x86_64.~
As you need a pre-built kernel source, such as USB Wifi driver or you like to change a build option for the kernel, you can complete these tasks only on Raspberry Pi 2. You do not need any other platforms.~
~
The self-compiling process is the same to both Raspbian Wheezy and Jessie.~

**Required packages [#w3b76267]
>
Please install required packages for building kernel.
 $ sudo apt-get install bc ncurses-dev
gcc, make, and git are already included. For Wheezy, the version of gcc is 4.6.3, and the version of gcc for Jessie is 4.9.2.~
~
The differences between versions do not affect on the build process of kernel source, but this would affects on the build of kernel sources for external drivers. Since the differences in gcc options and macro, the driver sources due to differences in version of gcc are needed to be modified.~

** Obtaining kernel source [#t054625e]
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Moving to the directory of /usr/src, obtain the kernel source with git.~
 beat@raspberrypi ~ $ cd /usr/src/
 beat@raspberrypi /usr/src $ sudo -s
~
The main part of kernel~
 root@raspberrypi:/usr/src# git clone --depth 1 https://github.com/raspberrypi/linux.git -b rpi-4.1.y
 Cloning into 'linux'...
 remote: Counting objects: 52876, done.
 remote: Compressing objects: 100% (50356/50356), done.
 remote: Total 52876 (delta 4012), reused 17583 (delta 1851), pack-reused 0
 Receiving objects: 100% (52876/52876), 142.62 MiB | 1.96 MiB/s, done.
 Resolving deltas: 100% (4012/4012), done.
 Checking connectivity... done.
 Checking out files: 100% (49946/49946), done.
~
Firmware~
 root@raspberrypi:/usr/src# git clone --depth 1 https://github.com/raspberrypi/fi
 rmware.git
 Cloning into 'firmware'...
 remote: Counting objects: 4077, done.
 remote: Compressing objects: 100% (2200/2200), done.
 remote: Total 4077 (delta 1702), reused 2305 (delta 1576), pack-reused 0
 Receiving objects: 100% (4077/4077), 75.59 MiB | 1.21 MiB/s, done.
 Resolving deltas: 100% (1702/1702), done.
 Checking connectivity... done.
 Checking out files: 100% (3777/3777), done.
~
As of October 15 2015, the kernel version at rpi-4.1.y branch is 4.1.10.~
**Preparation for the build precess [#i434872b]
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Please move to the directory where the kernel source is checked out. To load the configs module, obtain config of the kernel, which is currently running. Then, prepare for the build process~
 root@raspberrypi:/usr/src/linux# cd linux
 root@raspberrypi:/usr/src/linux# modprobe configs
 root@raspberrypi:/usr/src/linux# zcat /proc/config.gz > .config
 root@raspberrypi:/usr/src/linux# cp ../firmware/extra/Module7.symvers Module.symvers
 ~
Resulting on config~
 root@raspberrypi:/usr/src/linux# make oldconfig
 scripts/kconfig/conf  --oldconfig Kconfig
 #
 # configuration written to .config
 #
Since the version of new config is identical to the version of currently running config, the preparation ends without asking whether to make newly added options effective or not.~


** Build process [#v8036c0c]
>
Let's start the build process.~
Because CPU of Raspberry Pi 2 has 4 cores, zImage, modules, and dtbs can be built collectively, utilizing the four-parallel execution of 4 cores with -j4 option. However, the four parallel execution consumes a lot of memory it requires to set swap. Without setting swap, a hung will occur in the middle of build process. Therefore, the three kernel sources are built one by one. During the build process, the build time is also measured by time command.~
~
zImge~
 root@raspberrypi:/usr/src/linux# time make zImage 2>&1 | tee make1.log
 ~~ Skipping ~~
   LD      arch/arm/boot/compressed/vmlinux
   OBJCOPY arch/arm/boot/zImage
   Kernel: arch/arm/boot/zImage is ready
 
 real    76m45.564s
 user    76m33.100s
 sys     3m42.070s
~
modules~
 root@raspberrypi:/usr/src/linux# time make modules 2>&1 | tee make2.log
 ~~ Skipping ~~
   IHEX    firmware/yam/1200.bin
   IHEX    firmware/yam/9600.bin
 
 real    214m43.233s
 user    204m52.790s
 sys     10m32.480s
~
dtbs~
 root@raspberrypi:/usr/src/linux# time make dtbs 2>&1 | tee make3.log
 ～～ 中略 ～～
   DTC     arch/arm/boot/dts/overlays/w1-gpio-pullup-overlay.dtb
   DTC     arch/arm/boot/dts/bcm2709-rpi-2-b.dtb
 
 real    0m10.528s
 user    0m3.110s
 sys     0m1.650s


**Installation [#q3b810e7]
>
Because these are self-compiled, they can be installed without any modification.~
~
Modules~
 root@raspberrypi:/usr/src/linux# make modules_install
 ~~ Skipping ~~
   INSTALL /lib/firmware/yam/9600.bin
   DEPMOD  4.1.10-v7+
~
dtb~
 root@raspberrypi:/usr/src/linux# ls arch/arm/boot/dts/*.dtb
 arch/arm/boot/dts/bcm2709-rpi-2-b.dtb
 root@raspberrypi:/usr/src/linux# cp arch/arm/boot/dts/*.dtb /boot/
~

>
 root@raspberrypi:/usr/src/linux# cp arch/arm/boot/dts/overlays/*.dtb /boot/overlays/
 root@raspberrypi:/usr/src/linux# cp arch/arm/boot/dts/overlays/README  /boot/overlays/
~
zImage~
Raspbian stores two zImages at /boot/ directory.  The one zImage (kernel.img) is for Raspberry Pi, and the other zImage (kernel7) is for ARMv7, including Raspberry Pi 2. zImage for Raspberry Pi 2 is replaced with newly build one.~
 root@raspberrypi:/usr/src/linux# cp /boot/kernel7.img /boot/kernel7.img.old
 root@raspberrypi:/usr/src/linux# scripts/mkknlimg arch/arm/boot/zImage /boot/kernel7.img
 root@raspberrypi:/usr/src/linux# ./scripts/mkknlimg arch/arm/boot/zImage /boot/kernel7.img
 Version: Linux version 4.1.10-v7+ (root@raspberrypi) (gcc version 4.9.2 (Raspbian 4.9.2-10) ) #1 SMP PREEMPT Fri Oct 16 22:21:16 JST 2015
 DT: y
 283x: n

** Rebooting [#s4b961ee]
>
To boot from the newly built kernel, please reboot the system.~
 # reboot
~
To check whether the newly build kernel is working or not, please look at the status. Please apply the command line below. (The other line is its return.)~
 pi@raspberrypi:~$ uname -a
 Linux raspberrypi 4.1.10-v7+ #1 SMP PREEMPT Fri Oct 16 22:21:16 JST 2015 armv7l GNU/Linux
~
To look at the status, if the new kernel is working, uname -a and local setting at build kernel are changed.~
 pi@raspberrypi:~$ uname -a
 Linux raspberrypi 4.1.10-v7+ #821 SMP PREEMPT Sat Oct 10 00:16:28 BST 2015 armv7l GNU/Linux

*Revision History [#ue3c0e62]
>
-2016-02-15 This document is initially released
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