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

[J.C. Wren]

        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
commands.

        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).

        --John


-----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
too.

Please keep us informed about your progress.

/Jesper

----- 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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