AVR-Chat

Graham Davies said:
> Here is something I've learned by experience and verified with Atmel
> support. If you have an AVR MCU that has JTAG support, you can get  into
> the device even if there is no MCU clock. You can't run and
> debug a program, but you can get in to repair mis-set clock selection
> fuses. Is that neat, or what?
>
> Here's what happened. I was bringing up a new board with an
> ATmega169. I am convinced that programming without in-circuit debug  is
> like tight-rope walking without a net, so I insist on bringing out  the
> JTAG interface.  But, I can't use it until I get the JTAG enable  fuse
> programmed, so I have to use in-system programming as well. So,  I'm
> connected up to an STK500, I've read the fuses out, checked the  JTAG
> enable fuse checkbox and hit write. This is when the weight of  cables
> hanging off the desk pulls my very light board down and breaks  the
> power connection. When I put it all together again, the in-system
> programming link is dead. I figured I was hosed, but in desperation I
> hooked up my JTAG-ICE clone and, lo and behold, it worked. The JTAG
> fuse got programmed, but the clock setting fuses got messed up too  and
> the MCU was waiting for an external clock. I fixed this and
> everything is fine again. Atmel support confirms that the JTAG
> interface does *not* need an MCU clock for programming and uses its
> own. ISP, however, requires a correctly configured clock source.

As a FPGA designer, this is not surprising...  One of the JTAG signals
*is* a clock and the only other thing you usually need is power.

> In case anyone is interested, the JTAG-ICE clone is of my own rather
> unique design and you can see what it looks like here:
> http://www.ecrostech.com/Other/BflyCarrier.jpg
> I have been thinking about making both it and the Butterfly Carrier
> board shown in the picture into products but I can't get a reading on
> how well they might sell.  I would slightly undercut the other clones
> for the JTAG-ICE at, say, $39.95 and the Butterfly Carrier bare board
> would be $9.95.

Looks good to me...   I could use both of these about now.

Besides AVR Studio is there any other software (i.e. GDB) that
supports JTAG debugging now on the AVR?

Mike