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Re: [avr-gcc-list] Fw: Make Your Own JTAGICE box

From: Jason Kyle
Subject: Re: [avr-gcc-list] Fw: Make Your Own JTAGICE box
Date: Fri, 25 Apr 2003 13:24:27 +1200

At 00:37 25/04/2003 +0200, Marek Michalkiewicz wrote:
On Fri, Apr 25, 2003 at 08:49:39AM +1200, Jason Kyle wrote:
> :)  Snooping the serial comms would show that up pretty quick and also
> allow an unobscured binary to be extracted, enabling those who don't use
> windows to program the micro without astudio.

Good example of fair use, I guess :)

> Still think it's way better to write something from scratch, especially
> given the max 200kHz JTAG clock the official firmware allows.

http://www.case2000.com/ocd.html has some info about these secret
JTAG commands, perhaps that may be helpful...

The serial port speed looks like a bottleneck for JTAG ICE anyway -
a parallel port JTAG interface may be faster (and cheaper, too).

USB is a much better option, makes is easy to run with very low voltage targets since the ICE can run at 5V from USB interface without external power. FTDI USB devices would be ideal since they have virtual com port drivers for most OS's and would also retain compatibility with existing software such as avraice and astudio. Just need to fix that time machine first.....

> Ironically, i've been working on a 3DES encrypted STK500 protocol
> bootloader lately :)

Is it realistic (no large tables) to implement 3DES in the small
AVR bootloader area (max 8K on m128)?

Yes. Have written and tested DES for AVR, 1.25kB after much bashing head against table and walls :) 3DES being a fairly simple extension won't add much extra. Most of the table based implementations are only really suited to >= 32bit (maybe 16bit?) cpu where bit manipulation would be too wasteful. DES throughput is around 200kbps at 16MHz (somewhere around that anyway, didn't write it down at the time).

STK500 bootloader code is around the same size so >= m32 with 4kB boot block will do fine, although there's no reason why the DES code can't be stuck somewhere in application space and in fact I plan on doing this for some 2kB boot block devices.



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