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RE: [avr-gcc-list] r-engineering the JTAG-ICE protocol

From: J.C. Wren
Subject: RE: [avr-gcc-list] r-engineering the JTAG-ICE protocol
Date: Mon, 7 Oct 2002 15:44:33 -0400

        The issue will be getting the JTAG ICE to issue sufficiently atomic
commands to determine where one JTAG command picks up, and the other leaves
off.  Obviously, trying to program a 64K file isn't going to be a good idea.
But sending an erase command, determining that, then programming a single
byte should be sufficiently atomic.  Also, most JTAG commands tend to be
clocked out all at once, but a small delay should be able to be seen between

        I don't think any special hardware should be needed, at least as long as
speed isn't an issue.  A parallel port with a buffer should be plenty, since
JTAG only needs 4 to 6 lines (depending on how RESET is managed).


-----Original Message-----
From: address@hidden [mailto:address@hidden
Behalf Of Jesper Hansen
Sent: Saturday, October 05, 2002 10:16
To: Karl Ran; address@hidden
Subject: Re: [avr-gcc-list] r-engineering the JTAG-ICE protocol

Hi Karl,

I've been thinking of the same thing. Haven't started yet, but are
considering buying a JTAGICE so I can hack it.

The protocols is as you say synchronous, so a simple program
could be written on a mega16x or 8515 to log all the communication
between the ICE and the CPU being debugged.
Or, if it's too fast, the good old way with a storage scope works

Please keep us informed about your progress.


----- Original Message -----
From: "Karl Ran" <address@hidden>
To: <address@hidden>
Sent: Saturday, October 05, 2002 3:23 PM
Subject: [avr-gcc-list] r-engineering the JTAG-ICE protocol

> Hi there!
> I'd like to know if anyone already started to reverse-engineer the
> AVR-onchip-JTAG-ICE command-set on the newer Mega16++ AVRs.
> If not, anyone knows the complexity of the ICE command-sets on the
> microconrollers in general?
> I realy wonder why Atmel put a big Mega163 in its JTAG-RS232 interface.
> How hard can it be?
> JTAG is synchronouns protocol, AFAIK. So it should be quite easy to
> capture, right?
> I'd guess the (binary) commands could look like these:
> Set bp as/ds
> Clr bp as/ds
> read mem
> write mem
> read reg
> write reg
> set pc
> read ICE-status
> read adr-bus history
> stop
> start
> ..
> Am I totaly on the wrong track here?
> Any tips, infos, etc are welcome!
> Karl
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