OpenWrtDocs/Hardware/AVM/FRITZ!Box SL
I've successfully booted my Box with the sources from svn checkout http://svn.openwrt.org/openwrt/trunk/openwrt
I made changes to target/linux/ar7-2.4/patches/003-net_driver_cpmac.patch to switch to the internal PHY as my device has only one PHY (and no external).
I've put some informations to http://www.wehavemorefun.de/fritzbox/OpenWRT