mrc.bin

All Haswell boards supported by coreboot currently require a proprietary blob in order to initialise the DRAM and a few other components. The blob, named mrc.bin, largely consists of Intel’s memory reference code (MRC), but it has been tailored specifically for ChromeOS. It is just under 200 KiB in size. Another name for mrc.bin is the system agent binary.

Having a replacement for mrc.bin using native coreboot code is very much desired, but it is not an easy task.

Obtaining mrc.bin

Unfortunately, it is not currently possible to distribute mrc.bin as part of coreboot. Though, it can be obtained from a Haswell Chromebook firmware image like so, starting in the root of the coreboot directory:

make -C util/cbfstool
cd util/chromeos
./crosfirmware.sh peppy
../cbfstool/cbfstool coreboot-*.bin extract -f mrc.bin -n mrc.bin -r RO_SECTION

Now, place mrc.bin in the root of the coreboot directory. Alternatively, place mrc.bin anywhere you want, and set MRC_FILE to its location when building coreboot.

ECC DRAM

When mrc.bin has finished executing, ECC is active on the channels populated with ECC DIMMs. However, mrc.bin was tailored specifically for Haswell Chromebooks and Chromeboxes, none of which support ECC DRAM. While ECC likely functions correctly, it is advised to further validate the correct operation of ECC if data integrity is absolutely critical.