Not a question, but thought others might be interested...
I've always had difficulty getting into and out of debugWire in AS6.1 with my Dragon. Maybe that's pretty much typical--I haven't gotten any replies here when I asked for a step by step procedure.
But now I'm seeing something that suggests I have (and maybe always have had) a Dragon hardware problem...
I've been chasing what looked like "bus contention" on the MISO signal from SPI peripherals to the Atmega328p. The signal is shared between two NRF24L01 transceivers, but only one is enabled at a time by their associated csn signals. It looks like bus contention since the down level output is only around 1 volt when driven from one transceiver, about 1.1V when driven by the other.
I've not noticed this until now, since that down level is apparently low enough to be recognized as a logic 0 by the Atmega. The code executes properly. But, I needed to go after what's causing it--I thought maybe I had a firmware bug that had both chips on the SPI bus enabled at the same with one driving high, the other low. This would result in some intermediate voltage level like I was seeing. Or perhaps the Atmega didn't really have the MISO pin configured as an input.
Or, maybe a hardware short on my pcb from Miso to through something resistive to +5.
However, I just noticed that when I remove the header from the dragon, the MISO down levels look good--essentially zero volts. It doesn't matter whether the dragon is in debugWire or SPI mode--the MISO voltage level is never below 1 volt (but communication on the SPI still works with the marginal down level).
Next I used a six pin header in the socket from the dragon and measured between gnd and MISO--there's 1.2 volts DC. Should be floating or relatively high impedance.
I was going to try to use a resistor to pull it up and down to get the source impedance that the Dragon is driving MISO. But first I took a close look at the Dragon under a microscope.
I found a six pin part "tombstoned" just above the Mega 128 and just to the left of what looks like a Xtal on the Dragon. I touched that part with my finger, and it just fell off. Solder bumps on the lands look like they never reflowed to the pins on one side.
I'm tempted to solder the part back on the board, but don't want to void any warranty that might exist on the Dragon. I'll have to search my email folders to figure out who I bought it from and how to check for warranty, unless Atmel will make it good for me.
Anyone had experience getting replacements for defective debugging hardware?