DKU-5 versus ARM-USB-OCD (updated)

For some time I've been unable to access my ED Mini's console.

This was not a fault in the wiring or a failure of the DKU-5 cable. This is a fault of the Linux kernel on my host, development, machine: it freezes completely when opening the /dev/ttyUSB0 device which represents the DKU-5 cable; and when I say 'freeze', I mean it. Mouse pointer dead. Keyboard dead. Filesystems not synced. Only way out is reset or, as my computer does not have a reset button, forced power-off.

I don't like that at all.
<!--break--!>
Investigations showed that some Ubuntu and Redhat users experienced the same issue, with variants. It looks like recent kernels have the issue; I could downgrade my kernel... Or I could switch from the DKU-5 cable to the serial on my Olimex ARM-USB-OCD JTAG probe, which I knew was not causing trouble with Linux.

That meant unsoldering the end of the DKU-5 cable from the 8-pin header on the ED Mini, and re-soldering again... Which I was becoming tired of. So I decided I'd rather add a connector to the ED Mini once and for all.

I chose a DB-9 female connector for two reasons. First, it's the most common connector with close to 8 lines. Second, its ninth hole can easily be filled in to make sure no one will plug a normal male DB-9 in it by mistake.

First thing was to drill the casing...

... then adding the DB-9...

... then drilling the backplate and putting it back in place.

Now the next phase was to build a splitter which would connect to the ED Mini's female DB-9 and split out to a 20-pin JTAG connector on one side and a male DB-9 RS-232 plug on the other side. Of course, the splitter has to do the level conversion between the ED Mini's 3.3v serial console and the theoretical +12/-12 (actually +5/-5) RS-232.

[picture of the splitter coming up soon]

Actually the splitter is not 100% complete yet: it lacks two resistors that will provide a 3.3v reference voltage for the JTAG probe from the 5v source on the ED Mini. However, the serial part is complete, which allows me to go back to software development. :)