"Bricking" the Xmega
What? Not possible? Think again.
"Think" being the key word, and obviously NOT what I was doing last night.
It is well known that the easiest way to "Brick" a Mega or Tiny is to set the fuses to a non-existance clock source.
One can't do this in the Xmega, because they always start up on their internal RC Osc at 2 MHz.
As far as I know although the JTAG interface can be disabled, the PDI interface is always live.
So, how would one "Brick" their Xmega?
Set the Brownout Detector for 3.2 V and run it at just under that!
It will then be in a constant state of Brownout Reset, which is NOT over ridden by the PDI interface.
One then can't read the signature, or get to the Fuses to reset it.
Fortunately, it is recoverable. Just power the Xmega at 3.6 V, (> 3.2 V), and it will come alive again, allowing one to reset the Brownout threshold, or disable it altogether.
(My power supply, by the way, is 3.285 V, ( > 3.2 V), so there must be a little "error" in the 3.2 V threshold. I wasn't planning on running it that closely to the power supply, I was testing the ability to set fuses with my programmer...)
Perhaps my mentioning this will save someone else from making this blunder. :oops: