debrick with serial?

Johannes Zellner

Hi,

it seems that I bricked my omega while upgrading.
Is there a way I can debrick with a serial connection?
I already managed to get into uboot with a serial terminal, but I don't know what do do next w/o ethernet expansion.

If it's not possible w/o ethernet expansion:
Can I just connect the four omega pins rx-, rx+, tx-, tx+ to the corresponding pins of an ethernet cable to get an ethernet connection?

Pedro Baco

Can't you access it via uart-usb bridge as described in https://wiki.onion.io/get-started ?

Johannes Zellner

Yes, I'm using serial over USB Form a Linux PC to geht into the uboot Form the omega. But the image is broken, so the omega won't boot.

Pedro Baco

It seems that the only way is with the ethernet expansion. I've seen in another post a possible factory reset by doing the following : After the 20-25 second mark after boot, try holding the Reset button for about 10 seconds and releasing. This will perform a factory reset. Connecting direcly an ethernet cable is not possible, since the ethernet connectors actually have inside some circuitry which can't be bypassed, but you could actually use one of those connectors and link it up to those pins.

Boken Lin

@Johannes-Zellner No, unfortunately, there's no way to debrick via serial connection. And you need the transformer that's on the ethernet expansion to modulate the signals, so connecting them directly to an ethernet cable won't work...

Johannes Zellner

if I don't want to wait for the ethernet expansion to be shipped ....

can I connect the bricked omega with another omega via a crossover cabling like this?

Boken Lin

This post is deleted!

Zheng Han

@Johannes-Zellner What you have there will not work. You need to decouple the the DC current between the two Omegas.

!!! Works only in theory. Proceed at your own risk !!!

Transformerless Ethernet

Here you are essentially creating your own transformer to modulate the Ethernet signal. There is no exact requirement for the capacitors and resistors values, however capacitor shouldn't be too big. (for example: 0.1µF and 100Ω should work)

Give it a try if you are adventures or you can always fall back on an ethernet expansion.

Johannes Zellner

@Zheng-Han thanks. TX and RX should be crossed over, shouldn't they?

Zheng Han

@Johannes-Zellner They don't need to be crossed over. The ethernet driver should be able to handle that.

Johannes Zellner

@Zheng-Han : you're my hero! I just restored my bricked omega by connecting it via ethernet with a second omega. I built the network connection beween the two omegas just exactly as you suggested on a breadboard and it worked out of the box. Thanks a lot!

Here are the necessary steps after wiring the network connection:

boot the good omega -- let's call it omega-good
connect the bricked omega (omega-bricked) with an USB cable with a linux pc (expansion switch still off)
connect to omega-bricked with screen /dev/ttyUSB0 115200
power on the switch of the expansion board of omega-bricked and immediately hit enter in the screen session to get into uboot on omega-bricked
printenv in uboot on omega-bricked shows that the ethernet ip is configured to be 192.168.1.1
configure the ethernet connection of omega-good to use the static ip 192.168.1.100, either by modifying /etc/config/network and restarting the network or by something like ifconfig eth0 192.168.1.100 up
from uboot in omega-bricked verify with ping 192.168.1.100 that the network connection to omega-good works
from uboot in omega-bricked start httpd
create ssh tunnel from the linux pc to omega-bricked via omega-good with ssh -L 8080:192.168.1.1:80 omega-good (ssh connection to omega-good is via wifi)
open http://localhost:8080/ in a browser on the linux pc. The ssh tunnel redirects this to the httpd of omega-bricked → you see the uboot httpd upgrade page in your browser and can proceed to upload a bin image.

Boken Lin

@Johannes-Zellner Do you mind if we put this up on our Wiki? This would be a really helpful article for users who have bricked their Omega but do not have an ethernet expansion to de-brick it.

Johannes Zellner

@Boken-Lin sure — feel free to put it in the Wiki. I'd be glad if it it's helpful for others.

Boken Lin

@Johannes-Zellner Thanks! That's some first class hacking right there! Great job for making it work!