First, you need the following binary blobs:
- descriptor.bin - Intel flash descriptor
- me.bin - Intel Management Engine
- mrc.bin - Memory Reference Code, which sets up SDRAM
- video ROM - sets up the display
You can get these binary blobs by:
$ git clone http://review.coreboot.org/p/blobs.git
$ cd blobs
Find the following files:
The 3rd one should be renamed to mrc.bin.
As for the video ROM, you can get it here and rename it to vga.bin.
Make sure all these binary blobs are put in the board directory.
Now you can build U-Boot and obtain u-boot.rom:
$ make chromebook_link_defconfig
$ make all