I assembled my apu2e4 and prepared a 8GB USB-Stick (bootable, FAT) with
- root@alef:/mnt# ls -lF
- -rwxr-xr-x 1 root root 8388608 Aug 13 17:55 apu2_v4.14.0.3.rom*
- -rwxr-xr-x 1 root root 85 Aug 13 17:55 apu2_v4.14.0.3.SHA256*
- -rwxr-xr-x 1 root root 566 Aug 13 17:55 apu2_v4.14.0.3.SHA256.sig*
- -rwxr-xr-x 1 root root 156 Mai 15 2017 autostart.sh*
- -rwxr-xr-x 1 root root 19839127 Aug 2 2017 core.gz*
- -rwxr-xr-x 1 root root 1500 Sep 2 2016 syslinux.cfg*
- -rwxr-xr-x 1 root root 4103744 Jul 20 2016 vmlinuz*
So far, everything fine.
I put the USB-Stick in one of the 2 USB slots of the APU2E4, connected the serial cable with my machine and started a screen session. Then I plug in the power and the APU2E4 starts booting:
- screen /dev/ttyUSB0 115200
- PCEngines apu2
- coreboot build 20170228
- 4080 MB ECC DRAM
- SeaBIOS (version rel-1.10.0.1)
- Press F10 key now for boot menu
- Select boot device:
- 1. USB MSC Drive USB DISK 2.0 PMAP
- 2. ata0-0: KingFast ATA-10 Hard-Disk (111 GiBytes)
- 3. Payload [memtest]
- 4. Payload [setup]
- Booting from Hard Disk...
Display More
I press '1' to start booting from the USB-Stick, the stick's LED blinks for some seconds but it always ends up with 'Booting from Hard Disk...' 
I tried 2 different USB-sticks (both 8GB).
Should I try another one? Or am I missing some fundamental stuff?
Thanks for any hint!
Regards
Andi