some more news:
Still with 6 cores, I've tested everything in QEMU.
Seems my first build of Coreboot was problematic.
Building a new one, I can reach the LiveCD on the KFSN4-DRE.
Definitely used microcode updates (didn't work without).
SeaBIOS is displayed every time on the external GPU.
So that's encouraging.
Downside: Still can't boot from the installed OS.
Also SeaBIOS doesn't show all my disks, for some reason.
Suggested things to try from #coreboot:
* fetch the SeaBIOS log.
* try VGA BIOS.
* Try GRUB only, properly configured
(set root=(hd0,msdos1) > linux /vmlinuz root=/dev/sda1 > initrd /initrd.img
> boot).
* Check SeaBIOS config (rather obscure advice since there's not much to
configure).
I need to make a copy of this rom, I'll gain time for recovery, if needed.
