Alright. I finally managed to boot initramfs and then sysupgrade a snapshot firmware.
But;
The documentation here references Luci for sysupgrade. Yet I couldn't access the Luci interface, so I thought perhaps the snapshot initramfs doesn't have Luci built-in.
So I ssh'ed into the router and sysupgraded manually. The first message was "Image metadata not found". But it got restarted and it even got an IP from a DHCP server with hostname "OpenWRT".
Now, the problem is the new IP it got from the DHCP server, I cannot ssh into it.
What am I missing here?
EDIT:
I just realized that the device restarts over and over again. Cannot reset either. I've tried everything written in failsafe documentation.
Well, the "enabling serial port" part. It is very confusing, as I don't understand if I need the original OS to do what it says, or if OpenWRT somehow supports RouterBOOT. Hell, I couldn't even understood if RouterBOOT is a software to be installed on computer, or something to be flashed as a bootloader for the device.
Also it says compiling the kernel with some flags to enable serial port, which is alright to some point; to the point where say I've compiled the kernel, how can I flash it onto the device if I don't have any access to failsafe or the serial port.
Device restarts repeatedly (after every 8-10 seconds). I can't get into failsafe mode via reset button, it doesn't get any IP from DHCP so I cannot ssh into it even for a brief moment.
I've ordered a new device and I'll try to flash snaphot OpenWRT again. Let's see what happens. I believe the device at hand is gone.
I fear the same thing would happen to the new device. What I don't understand is (this is the first I'm having this kind of problem during the last 5 years) how would a snapshot OpenWRT brick the device? What are the factors here that would result in such a behaviour?
My guess is that you should read this about Mikrotik Boot. Connect a Serial 3,3V TTL cable on the board, after you solder the pins (or hold them steadily). If you can see something, there is hope. If not, I don't think it will be worthy the time to fix it.
I can only speculate here. Could be faulty image, some error during uploading leading to corrupted image. If you cannot verify the integrity of the file after it is uploaded on the router, you can only cross fingers that all goes well.
I can't see anything after connecting to the serial port. It says in docs that initially the serial port is not enabled, there is a flag which kernel has to be compiled with; only after then I can see something on serial output.
Anyway; I'm gonna try the new one. Let's see what happens. I'll update here as soon as I can.
Understood.