Internal Debug Board

[Werner Almesberger]

The debug board is one of those love-hate things in Openmoko: it's
incredibly useful for kernel debugging but it's also fragile, a mess
to connect, and not particularly mobile.

More than one and a half years ago, Harald and I started tossing
around the idea of putting the debug board into the Neo, but we
couldn't see a useful way to accomplish this. Later, Andy suggested
to use a dedicated USB receptacle for such an internal debug board,
but this still left some unresolved issues.

Later on, there was also much discussion about adding an MCU that
could accomplish this, but we never found the right one and interest
inside Openmoko in solving the debug board issue has waned.

Recently, Andy mentioned some small USB-capable MCU:
http://lists.openmoko.org/pipermail/hardware/2008-October/000711.html

About a month ago, I finally had a look at those chips. It was love
at first sight :-) Here's the little fun project I did with them:

http://www.almesberger.net/misc/idbg/

Components are about USD 10 if purchased in single-digit quantities.
Add another USD 10 or so if you don't already have some very thin
wire (my pictures show wires with 0.8mm outside diameter, which is
about the maximum that will fit.)

Note: there are still quite a few loose ends. E.g., JTAG is
dreadfully slow, I2C doesn't work yet, and the boot loader doesn't
set the Flash protection. I also don't know how badly GPS resents
the presence of new signals and metallic objects in its vicinity.

Enjoy,
- Werner