These are the scripts used to compile the ev3dev kernel. Originally it also included scripts to bootstrap a root file system and create a disk image. Those scripts have evolved into the brickstrap package.

NOTE: The instructions below are for ev3dev-trixie. If you want to build a kernel for ev3dev-stretch, please use the ev3dev-stretch branch.

• Ubuntu LTS (can be run in a virtual machine or with Windows Subsystem for Linux)

• User account with sudo enabled

• Packages:

    sudo apt-get update
    # then install required packages
    sudo apt-get install git build-essential ncurses-dev fakeroot bc \
    u-boot-tools lzop flex bison libssl-dev gcc-arm-linux-gnueabi
  

build-kernel Used to build the kernel.

defconfig Used to manage the *_defconfig file and your current local configuration (.config).

menuconfig Runs the menu configuration tool for the kernel configuration.

1. Create a working directory somewhere. For this tutorial, we are using ~/work. The build scripts will generate extra subdirectories here so we suggest creating a new directory instead of using an existing one.

   ~ $ mkdir work
   ~ $ cd work
   

2. Clone this repo and also the ev3-kernel repo (or rpi-kernel or bb.org-kernel), then make sure the lego drivers submodule is up to date (we don't always update the submodule commit in the kernel repo, so you have to pull manually to get the most recent commits).

   ~/work $ git clone https://github.com/ev3dev/ev3dev-buildscripts
   ~/work $ git clone --recursive --depth 25 -b ev3dev-trixie https://github.com/ev3dev/ev3-kernel 
   

3. Change to the ev3dev-buildscripts directory and have a look around.

   ~/work $ cd ev3dev-buildscripts
   ~/work/ev3dev-buildscripts $ ls
   boot.cmd        build-kernel  LICENSE    menuconfig  setup-env
   build-boot-scr  defconfig     local-env  README.md
   

4. Create a local-env to make use of all of your processing power. See the Faster Builds and Custom Locations section below for more about this file.

   ~/work/ev3dev-buildscripts $ echo "export EV3DEV_MAKE_ARGS=-j4" > local-env
   

5. Now we can compile the kernel.

   ~/work/ev3dev-buildscripts $ ./build-kernel
   

   For Raspberry Pi and BeagleBone Black we need to set an environment variable.

   # Rapsberry Pi 1
   EV3DEV_KERNEL_FLAVOR=rpi ./build-kernel
   # Raspberry Pi 2
   EV3DEV_KERNEL_FLAVOR=rpi2 ./build-kernel
   # BeagleBoard
   EV3DEV_KERNEL_FLAVOR=bb.org ./build-kernel
   

6. That's it! The uImage and kernel modules you just built are saved in ./build-area. You just need to copy the files to your already formatted SD card. For an easier way of getting the kernel on your EV3, see Sharing Your Kernel. Starting with ev3dev-stretch images dated 2018-05 or later, the uImage file is no longer used. Create a Debian package as described in the Sharing Your Kernel section.

   ~/work/ev3dev-buildscripts $ cd ./build-area/linux-ev3dev-ev3-dist
   ~/work/ev3dev-buildscripts/build-area/linux-ev3dev-ev3-dist $ cp uImage <path-to-boot-partition>/uImage
   ~/work/ev3dev-buildscripts/build-area/linux-ev3dev-ev3-dist $ sudo cp -r lib/ <path-to-file-system-partition>
   

By default the locations of the kernel source tree and the toolchain used to build the kernel are expected to be in certain directories relative to the ev3dev-buildscripts repo directory.

You can override these locations by creating a file called local-env in the ev3dev-buildscripts directory or ~/.ev3dev-env (in your home directory). It should look like this:

#!/bin/sh

export EV3DEV_MAKE_ARGS=-j4

# override any EV3DEV_* variables from setup-env script.
#export EV3DEV_XXX=/custom/path
#export EV3DEV_MERGE_CMD="kdiff3 \$file1 \$file2"
#export EV3DEV_MERGE_CMD="meld \$file1 \$file2"

The -j4 is for faster builds. It allows make to compile files in in parallel. You should replace 4 with the number of processor cores that you want to devote to building the kernel.

You can use custom paths to make the build-kernel script automatically install the kernel and modules directly on the EV3! First, you need to mount the EV3 root file system. You can use nfs or sshfs (check the wiki on how to do this). Then just set the appropriate paths in your local-env like this:

# replace `/mnt/ev3dev-root` with your actual mount point
export EV3DEV_INSTALL_KERNEL=/mnt/ev3dev-root/boot/flash
export EV3DEV_INSTALL_MODULES=/mnt/ev3dev-root

When you run ./build-kernel if no existing kernel configuration exists the default configuration is loaded from arch/arm/configs/ev3dev_defconfig.

If you make changes to your local kernel configuration that you want to merge into the default configuration, run ./defconfig update. It will use the merge tool specified by the EV3DEV_MERGE_CMD environment variable.

If you have an existing kernel configuration, you will want to check for changes to the default configuration each time you merge or checkout a branch. You can call ./defconfig load to wipe out your local configuration and load the default configuration or you can call ./defconfig merge to merge the default configuration into your existing local configuration.

If you are forgetful or lazy or just want this to happen automatically, you can set up hooks in your git repo. For example, you could save the following file as both .git/hooks/post-merge and .git/hooks/post-checkout and you will be prompted to merge the default configuration into your local configuration whenever you merge or checkout a branch. In you followed the tutorial above, <path-to-ev3dev-buildscripts-repo> would be ~/work/ev3dev-buildscripts.

#!/bin/sh

<path-to-ev3dev-buildscripts-repo>/defconfig merge

Want to send your custom kernel to someone so that they can use it? Never fear, there is an easy way to do that - using Debian packaging.

Make sure to install debhelper with:

sudo apt-get install debhelper

First, we want to set a kernel option so that our friends will know what kernel they are running. Run ./menuconfig and set this option:

General setup --->
  (-your-name-ev3) Local version - append to kernel release

Make sure to include the '-' prefix in -your-name on the Local version. And, of course, substitute something like your github user name for your-name. It is also important that the kernel release ends with -ev3 so that flash-kernel will recognize it as a "good" kernel and install it automatically.

Then, we build a Debian package.

~/work/ev3dev-buildscripts $ ./build-kernel bindeb-pkg KDEB_PKGVERSION=1
...
<lots-of-build-output>
...
~/work/ev3dev-buildscripts $ ls ./build-area/*.deb
./build-area/linux-headers-3.16.7-ckt9-5-ev3dev-your-name-ev3_1_armel.deb
./build-area/linux-image-3.16.7-ckt9-5-ev3dev-your-name-ev3_1_armel.deb
./build-area/linux-libc-dev_1_armel.deb

Now, send the linux-image-* file to your friend with these instructions:

• Copy the .deb file to your EV3
• Install the package
• Reboot the EV3

Example:

user@host ~ $ scp linux-image-*.deb otheruser@ev3dev:~
user@host ~ $ ssh otheruser@ev3dev
otheruser@ev3dev:~$ sudo dpkg --install ~/linux-image-*.deb
otheruser@ev3dev:~$ sudo reboot

• If you see this error...

    ERROR: ld.so: object 'libfakeroot-sysv.so' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS64): ignored.
  

  ...just ignore it. It is normal (a side effect of cross-compiling).

• If you see an error related to asm/bitsperlong.h like this:

    ...
      Generating include/generated/mach-types.h
      CC      kernel/bounds.s
    In file included from /home/user/ev3-kernel/arch/arm/include/asm/types.h:4:0,
                     from /home/user/ev3-kernel/include/linux/types.h:4,
                     from /home/user/ev3-kernel/include/linux/page-flags.h:8,
                     from /home/user/ev3-kernel/kernel/bounds.c:9:
    /home/user/ev3-kernel/include/asm-generic/int-ll64.h:11:29: fatal error: asm/bitsperlong.h: No such file or directory
    compilation terminated.
    make[2]: *** [kernel/bounds.s] Error 1
    make[1]: *** [prepare0] Error 2
    make: *** [sub-make] Error 2
  

  Then you need to clean your kernel source tree like this:

     user@host ~/ev3-kernel $ git clean -dfX
  

If you want to update your kernel, rebase!

git remote add stable https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
git fetch stable tag v6.12.y # with 'y' being the latest version 
git rebase v6.12.y

If you want to update the submodules in the ev3-kernel (or you forgot to initialize them):

git submodule update --init --recursive --remote