If you just want to use ev3dev, please see the main ev3dev repository.

If you want to build the ev3dev kernel or root file system, read on.

ev3dev-rootfs

These are the scripts used to compile the ev3dev kernel and build the root file system.

System Requirements

• Debian or derivative OS (Ubuntu, Mint, etc.)
• User account with sudo enabled

Scripts

build-kernel Used to build the kernel.

defconfig Used to manage the ev3dev_defconfig file and your current local configuration.

install-kernel-build-tools Installs the prerequisite tools required to build the kernel.

menuconfig Runs the menu configuration tool for the kernel configuration.

First time kernel build

1. If you don't have git already, then we need to install it.

   ~ $ sudo apt-get install git
   

2. 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
   

3. Clone the kernel and root file system repos.

   ~/work $ git clone git://github.com/mindboards/ev3dev-kernel
   ~/work $ git clone git://github.com/mindboards/ev3dev-rootfs
   

4. Change to the ev3dev-rootfs director and have a look around.

   ~/work $ cd ev3dev-rootfs
   ~/work/ev3dev-rootfs $ ls
   build_ev3dev_setup          menuconfig         sdcard-img-mount
   build_extras                multistrap.conf    sdcard-img-populate
   build-kernel                README.md          update-defconfig
   install-kernel-build-tools  rootfs-create
   LICENSE                     sdcard-img-create
   

5. Now we need to install the required tool. TO do this, just run the install-kernel-build-tools script. (You only need to run this once.)

   ~/work/ev3dev-rootfs $ ./install-kernel-build-tools
   

6. 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-rootfs $ echo "#!/bin/sh
   
   export AM1808_MAKE_ARGS=-j4" > local-env
   

7. Now we can compile the kernel.

   ~/work/ev3dev-rootfs $ ./build_kernel
   

8. That's it! The uImage and kernel modules you just built are saved in ``../dist```. You just need to copy the files to your already formatted SD card.

   ~/work/ev3dev-rootfs $ cd ../dist
   ~/work/dist $ cp uImage <path-to-boot-partition>/uImage
   ~/work/dist $ sudo cp -r lib/ <path-to-file-system-partition>
   

Faster Builds and 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-rootfs repo directory.

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

#!/bin/sh

export AM1808_MAKE_ARGS=-j4

# override any AM1808_* variables from setup-env script.
#export AM1808_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.

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. If you want to selectively merge changes, run ./defconfig update -i which will open 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-rootfs-repo>`` would be ~/work/ev3dev-rootfs```.

#!/bin/sh

<path-to-ev3dev-rootfs-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 need to change a couple kernel options to add some version info so that our friends will know what kernel they are running. Run ./menuconfig and set the following options:

General setup --->
  (-your-name) Local version - append to kernel release
  [*] Automatically append version information to the version string

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. Also, I don't recommend leaving the second option enabled during regular development, otherwise every time you make a commit, you will have to reload the kernel on your EV3 even if you only made changes to modules.

Now, make sure that your git repo is clean (or your kernel version will say dirty).

~/work/ev3dev-kernel $ git status
# On branch awesomeness
nothing to commit, working directory clean

Then, we build a Debian package (with a crazy huge file name).

~/work/ev3dev-rootfs $ ./build-kernel deb-pkg KDEB_PKGVERSION=1
...
<lots-of-build-output>
...
~/work/ev3dev-rootfs $ ls ../*.deb
../linux-headers-3.3.0-ev3dev-00.01.02-your-name-g04254fb_1_armel.deb
../linux-image-3.3.0-ev3dev-00.01.02-your-name-g04254fb_1_armel.deb
../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
• Overwrite the existing uImage file on the FAT partition with the new one
• Reboot the EV3

Example:

user@host ~ $ scp linux-image-*.deb root@ev3dev:/tmp
user@host ~ $ ssh root@ev3dev
root@ev3dev:~# dpkg --install /tmp/linux-image-*.deb
root@ev3dev:~# cp /boot/uImage-3.3.0-ev3dev-00.01.02-your-name-g04254fb /media/mmc_p1/uImage 
root@ev3dev:~# reboot