Yeah, that brings me a memory!!
I did used that years ago - found my post on PCengines Forum:
I did exactly like then and it worked: apparently the older version 0.9 of flashrom was the SOLUTION for APU1C- at least this is what I wrote in that post in PCEngines forum
I am old, don’t mind me.
And HUGE thanks
Here is my APU now
**PC Engines apu1coreboot build 20190711 **
BIOS version v4.10.0.3
And from IPFire
> [root@blue-i586 ~]# firmware-update info
> Board : PC Engines apu1
> HW Version : 1.0
> Serial : 871955
> BIOS Version: v4.10.0.3 (11/07/2019)