Hi Stephen,
The MinnowBoard ships with UEFI firmware, which is an open firmware
environment. It does require a couple of binary blobs for the platform
initialization code, but the remainder should be open and rebuildable.
This site is the main source of information to get you started with
firmware development on the MinnowBoard:
http://uefidk.intel.com/content/minnowboard-uefi-firmware
Scott
--
Scott Garman
Embedded Linux Engineer - Yocto Project
Intel Open Source Technology Center