Zyxel nsa320s won't boot (7 replies)

I have installed latest uboot (and configured netcat) as described in the sticky thread - as I understood it would allow me to boot from all the media usb/hdd/flash.

But after rebooting, zyxel won't load original firmware, LAN led blinks for a second, and power led goes from solid green to flashing amber.

I have tried to create bootable pendrive with debian as described in: http://forum.doozan.com/read.php?2,12096

- created single ext3 partition with rootfs label,
- extracted latest debian image (Debian-3.18.5-kirkwood-tld-1-rootfs-bodhi.tar.bz2) to it (as root),
- created embedded DTB (I had to take DTB from the newer kernel 4.4 because there was no such file in debian archive):

cd /media/sdb1/boot
cp -a zImage-3.18.5-kirkwood-tld-1  zImage.fdt
cat dts/kirkwood-nsa320s.dtb  >> zImage.fdt
mv uImage uImage.orig
mkimage -A arm -O linux -T kernel -C none -a 0x00008000 -e 0x00008000 -n Linux-3.18.5-kirkwood-tld-1 -d zImage.fdt uImage
sync

When I try to boot from pendrive, zyxel tries to read from it and the led goes from solid green to flashing green/amber.

How can I force nc to work? I tried several tools (OS X) and I am sure I have my IPs set properly.

Apart from rs232 - how can I debug this behaviour?