OpenPhoenux Serial Console Access

08 July 2012, 10:31 UTC

I find that serial console access is a must for debugging kernel problems on the GTA04 board in my OpenPhoenux phone. Getting serial console access to the board itself is quite easy as it has a little connector on the board, and came with a ribbon cable which plugs in to this connector and has a DB-9 on the other end.

However it isn't so easy when the board is in the phone case, which is where it is most useful. The connector is on the side of the board closest to the front of the phone, just above the display. Cutting a hole there might be possible, but having a ribbon cable hanging out isn't really an option. So I needed to be a little more clever.

Firstly I destroyed the ribbon cable, keeping the brown, yellow, and blue wires and cutting the rest off at the plug. The three wires I kept about 2cm of length on. You can probably see some solder burns from an earlier experiment where I tried to solder 3 wires directly onto the pins at the back of the plug. That worked a little bit, but they kept breaking off. Maybe I'm not good a soldering, or maybe it was just a bad idea.

As you can see in this picture, the wires are feed around the edge of the board the the back. They are aiming for the little cavity beside the battery.

Then I cut away some plastic to make a hole big enough for a small cable with tap wrapped around it, shown here.

Next I found a nice small 3.5mm stereo jack of an old busted pair of headphone. Not all jacks are small enough. Ipod headsets seem to have particularly slim jacks, but others probably work as well. Soldering the 3 wires from this to the 3 wires from the ribbon cable means that I have TX, RX, GND in a reasonably accessible location.

You need to be careful about getting the length of the cable right so it is long enough without any excess. Here you see it tucked away so the back cover can go over. The tip of the jack goes into the slot a little bit and as you might be able to see, I have a little bit too much cable so it buckles a bit an uses more space than I would like. I can clip the back on though, which is all that matters.

Finally I bought a short cable with a female 3.5mm on one end (I think there were 2 RCA on the other), cut that up, and soldered the 3 wires to my DB-9. And now I get console access by just popping the cover over (being careful not to let the battery fall out), easing the jack out, and plugging it in. Very useful.