Re: [avr-gcc-list] Homebrew ICE?

[Joerg Wunsch]

As "Derick Schoonbee" <address@hidden> wrote:

>Does anybody have a recipe for a home made JTAG(??) / ICE?
>
>Something in likes of http://www.case2000.com/JtagIce/
>
>Would this be feasible? Any catches? 

It basically works for me, though i made mine with little more effort.
Basically, i've been thinking about level shifters so at least a
target Vcc range of 2.7...5.0 V is possible which doesn't cover the
entire allowable range (could be as low as 1.7 V for e. g. the
ATmega169, and up to 6.2 V).

I'm even willing to make my design publically available, but i have to
re-edit the schematics, and re-route the board for this to be useful.
Of course, the prototype finally did experience some minor mistakes,
and i'd also like to optionally add an 78L05 for the power supply.
I'm not sure about the legal situation though: as long as we have to
rely on Atmel's firmware, it's sort of a grey zone.  I'd prefer it to
have an opensource firmware for it, but currently don't have the
resources to donate much time to the FreeICE project myself.

In case anybody's interested, pictures of the board can be found at

http://www.sax.de/~joerg/jtag-ice-1.jpg
http://www.sax.de/~joerg/jtag-ice-2.jpg

>(Performance/Debugging/Compatibilities/Price?)

See above: the biggest problem in case2000's simple recipe is the
missing level shifters.  The Atmel level shifters are ingenious (for
example, they work with a target Vcc less or above the ICE's Vcc), but
they require a lot of ``chicken food'', and obviously, in order to be
able to publish my design at all, i didn't want to copy their
circuitry.  So i redesigned it using some 74HC4050 etc. buffers.

Also, the original design does a lot of protection on the JTAG side
which is missing in this simple design, so if you accidentally drop a
mains power wire onto your target, you'll for sure also explode your
JTAG ICE.
-- 
J"org Wunsch                                           Unix support engineer
address@hidden        http://www.interface-systems.de/~j/