Bootloader Design

With having to support a wide variety of platforms, there is no other option, then using Das U-Boot as bootloader. A positive side-effect of this choice is the fact, that most of the platforms at the HTWG Konstanz already run Das U-Boot as bootloader and therefore the configuration for those platforms exist.

Sources

As directly derived from the requirements the mainline sources of U-Boot must be used. However there can't be any restriction to a specific version. To be able to run any platform with the mainline sources of U-Boot the possibility of applying user patches during build has to be considered.

Repository

The user specification, such as configuration of U-Boot and user patches for the mainline sources should be stored within a repository. Therefore each platform / version combination needs to get its own branch. E.g. two branches have to exist if U-Boot version 1.0 and 1.2 should be build for platform A.

Cross Target Support

As U-Boot has to be build for different architectures cross target support needs to be considered.

Build Process

As mainline sources have to be used, those sources need to be retrieved somehow before the build process. Two possible options to retrieve the sources are:

• Yocto Project
• Buildroot
• The User has to provide sources within the repository
• The sources have to be downloaded before each build process at runtime

Build Steps

Building U-Boot has to include the following steps:

1. Retrieve the build specifications from the U-Boot-repository
2. Retrieve the U-Boot sources
3. Apply required patches
4. (Cross-)Compile U-Boot for target architecture with config provided by the specifications
5. Create an archive from the necessary files.