UBB-JTAG: proof of concept with M1

Werner Almesberger werner at almesberger.net
Fri Jan 4 14:02:58 EST 2013

No breakout board could be considered universal if it doesn't also
support JTAG. I've now made a proof of concept implementation that
demonstrates this on the example of the Milkymist One.

All the protocol handling is done by UrJTAG. For simplicity, I use
the "gpio" cable driver, which accesses GPIOs through
/sys/class/gpio/...  and is therefore not exactly a speed demon.

This is what the whole setup looks like:


Since the JTAG interface of Milkymist One runs at 2.5 V while the
Ben uses 3.3 V, the adapter has a few voltage dividers acting as
level shifters:


Since I don't have a mating connector for J6 (2 mm pitch) at
home, I improvised by making individual cables with receptables
for 2.54 mm headers:


A README with all the gory details (there a few quirks), a
schematic drawing, and cut-out labels for the wires can be found

- Werner

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