OpenEmbedded "poky" with some sysmocom specific modifications. Mostly used only up to sysmocom release 201310, but the "pyro" branch is still used for 201705
OE-Core seems to unpack the kernel sources into another
directory now (e.g. to share the sources with builds for
modules). Use the kernel.bbclass kernel_do_configure and
copy the .config to the build directory.
The kernel is now built in a dedicated build directory.