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ev3dev-buildscripts

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-buster. If you want to build a kernel for ev3dev-stretch, please use the ev3dev-stretch branch.

The kernel builds published in releases are cut out of many functions and may not be suitable for use in any environment.

WARNING: Latest builds includes only RTL8818EU USB driver for WiFi. Any other WiFi adapter won't work. Also make sure lz4 is installed in your ev3dev and initramfs-tools configured to compress initrd in lz4 as of kernel supports only lz4 compressed initramfs.

Requirements

  • Ubuntu LTS (or Ubuntu LTS based distro)

  • User account with sudo enabled

  • Packages:

      sudo apt update
  sudo apt install git build-essential ncurses-dev fakeroot bc \
  u-boot-tools lzop flex bison libssl-dev crossbuild-essential-armel

Scripts

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.

First time kernel build

  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/StepanTheFlowey/ev3dev-buildscripts --branch ev3dev-buster
~/work:$ git clone --recurse-submodules --depth=1 --branch ev3dev-buster https://github.com/StepanTheFlowey/ev3-kernel
~/work:$ cd ev3-kernel/drivers/lego
~/work/ev3-kernel/drivers/lego:$ git pull origin ev3dev-buster
~/work/ev3-kernel/drivers/lego:$ cd -

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

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

  4. 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

  5. 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>

Custom locations

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 modifying a file called local-env in the ev3dev-buildscripts directory. It should look like this:

#!/bin/sh

export EV3DEV_MAKE_ARGS=-j`nproc` KCFLAGS="-pipe -w"
export HOSTCFLAGS=$KCFLAGS HOSTCXXFLAGS=$KCFLAGS

# 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"

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

Managing the kernel configuration

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

Sharing your kernel

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.

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 robot@ev3dev:~
user@host ~ $ ssh robot@ev3dev
robot@ev3dev:~$ sudo dpkg -i ~/linux-image-*.deb
robot@ev3dev:~$ exec sudo reboot

Common errors

  • 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