Nix expressions for (cross) building coreboot for gru-bob chromebook

These expressions allow building a coreboot ROM with a u-boot payload for the Rockchip RK3399-based "gru-bob" Chromebook (sold as ASUS C101PA). Lots of things are still hardcoded, but maybe this can serve as inspiration for others :)

Building

nix-build -A all produces a directory containing a bunch of handy files. The most important one is coreboot.rom.

Flashing

I've been flashing this using a SuzyQable. Initial setup for this was nontrivial, see write-protection.md.

For my user to do this, I need permissions to access a couple of things:

• Relevant USB device nodes in /dev/bus/usb/001/038 or similar (see lsusb)
• USB tty device nodes (/dev/ttyUSB[567] in my case)

Then I can flash (the Chromebook needs to be on at the beginning and will be forcibly turned off!):

./result/flashrom -p raiden_debug:target=AP -r backups/ap-$(date -Iminutes)
./result/flashrom -p raiden_debug:target=AP -w ./result/coreboot.rom

This takes quite a long time (usually ~10 minutes to write and verify for me).