This repository contains the source patches for u-boot and the linux kernel that are required to boot a blickwerk sensor.

All sources are released under the terms of the GPLv3+ unless stated otherwise in the source files or patches.

Blickwerk sensors use an i.MX 28 processor from Freescale Semiconductor (now part of NXP). All sensors are shipped with support for unencrypted bootstreams so that you can build your own u-boot and kernel image and run your software on them.

make prep-source will download the u-boot and kernel sources and will apply all patches.

make build will compile u-boot and the kernel sources using an arm cross-compiler.

make dist-deb will create a deb package that can be installed in a Debian distribution.

The make targets support different variants that control the boot behaviour. There are currently three distinct variants that can be set via the VARIANT environment variable. These are:

1. production

   • disables any u-boot boot delay
   • u-boot shell is deactivated
   • u-boot and kernel log are redirected to internal UART

2. development

   • u-boot delay is set to 3 seconds
   • u-boot shell is started by typing 'foo'
   • u-boot and kernel log are redirected to the external UART

3. init

   • u-boot delay is set to 3 seconds
   • u-boot shell is started by typing 'init'
   • u-boot mounts the ext2 filesystem on the second partition of the SD card and tries to execute the fuses.img file
   • u-boot and kernel log are redirected to the external UART

Note: The build system will build all three variants when building deb packages.

It is highly recommended, that you’ll build this kernel in a Debian environment. There’s a high chance, that you will encounter difficulties on other platforms, that are not covered by this guide.

In order to build a kernel you’ll need a few build dependencies. These are listed in the debian/control file in the line starting with Build-Depends. The names listed there are Debian packages that you can install with apt. You can’t do anything wrong: the debian build tools will abort relatively early into the build process in the event that you forgot something.

After you have installed the build dependencies you can continue with building the actual kernel and the .deb packages. The dist-deb make target from above will build the three kernel variants and the mxsboot tool, that is required in order to create bootstreams for SD cards. Continue by running:

make dist-deb DEBIAN_BUILDPACKAGE_COMMAND="dpkg-buildpackage -us -uc"

Once this task is finished (which might take a while), you’ll find a number of .deb files in the build/debian directory.

Note: The DEBIAN_BUILDPACKAGE_COMMAND override is necessary, to prevent the debian build tools from signing the .deb files. This is the default behaviour, but will fail because the email address used for signing is the one from the last debian/changelog entry.

The build targets only compile the kernel image, the u-boot image, and the kernel modules. But before you can create a system image you’ll need a kernel .deb package. If you haven’t already, refer to the previous section on how to build .deb packages.

In order to make the sensor boot an actual linux operating system there are a few prerequisites:

1. Make sure you have these tools in your PATH:
   • cdebootstrap-static, part of the cdebootstrap-static Debian package
   • mkfs.ext4, part of the e2fsprogs Debian package
   • guestfish, part of the libguestfs-tools Debian package
   • mkimage, part of u-boot-tools Debian package
   • elftosb
   • mxsboot, a deb package named imx28-mxsboot is part of this repository
2. Run scripts/image.sh create /path/to/a/linux-image-wurzelwerk-imx28-$variant.deb as root or via sudo
3. That’s it! There’s an .img file next to the .deb that you can now write to an SD card.

• deb packages are set to Architecture=all which indicates that they are architecture independent (they are not). This is an easy but dirty work-around to support cross-compilation on other platforms.

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