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[avr-chat] About JTAG...

From: Vincent Trouilliez
Subject: [avr-chat] About JTAG...
Date: Mon, 7 Apr 2008 22:18:18 +0200

Hi list,

I started an AVR project long ago, uses an ATmega32, programmed via ISP.
I am about to modify the hardware and while at it, would like to switch
from using ISP to using JTAG, so as to get experience in using JTAG in
its own right (since I never used it), as well as enjoy (I anticipate
it will be enjoyable ;-) the on-chip debugging features that the AVRs
offer via JTAG.

I am set on the programmer. Following advise from this list, the AVR
Dragon from Atmel, sounds ideal, especially since debugging is limited
to 32KB chips, and I happen to be using a mega32 so... that's good luck.


1) when I was using ISP, I found the "terminal" mode of
avrdude, to be truly invaluable. I looked at the man page for avrdude,
and it does say it supports the AVR Dragon in JTAG mode, but I am not
quite 100% sure from the man page, if the terminal mode is also
supported when using JTAG. The AVR datasheet does say that JTAG can
access the EEPROM, just not sure if avrdude can/does make use of it in
terminal mode.

2) I understand that the program to use for debugging is "avarice". 
I looked at the man page for it, and I thiiiiink the ATmega32/Dragon
combination is supported, but again, would love to have an explicit
confirmation from people who actually know for sure, from experience.

3) Does question 1) make sense at all ? I mean, when using gdb and a
GUI to debug the program via JTAG, can't the gdb GUI display (and
write) the contents of the EEPROM and Flash, in a similar fashion to
avrdude's terminal mode ? This way I would not have to switch
constantly to avrdude for terminal mode, then switch back the the
debugger etc.

4) if you feel I missed some JTAG related issue I should be aware
of, please tell me ! ;-)



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