Build the latest merged into the master git branch:
./build.sh --bleeding-edge x220
Latest stable release:
./build.sh x220
coreboot_lenovo-x220-complete.rom - The complete Coreboot ROM is the 8MB version used for internal flashing.
coreboot_lenovo-x220-complete.rom.sha256 - sha256 checksum of 8MB Coreboot Rom