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[avrdude-dev] Dragon DW->ISP USB reset question

From: John McCorquodale
Subject: [avrdude-dev] Dragon DW->ISP USB reset question
Date: Tue, 14 Dec 2010 16:08:40 -0800
User-agent: Mutt/1.5.20 (2009-06-14)


Just got my atmega328p on my spankin' new Dragon in debugWire mode and notice
what appears to be an old, well-understood situation:

  $ avrdude -c dragon_isp -P usb ...
  ISP connection fails cause DWEN fuse is set
  DW protocol to leave ISP ready occurs
  avrdude exits (*)

When avrdude exits and the libusb connection to the dragon closes, the dragon
resets, power cycling the atmega along with it, right back into DW mode.  Then
the subsequent avrdude call doesn't do the right thing, because the chip is
back in DW.

The answer is to supply an external power supply to keep the atmega up while
the dragon resets under it.

Sure, but here's my mindset: this clipping and unclipping of a wire in the
compile-load-debug cycle is distasteful.  (I have the atmega on a ZIF in the
dragon prototype area, not actually in-system.)

Here's my question (twofold):

  (1) Is it really that hard to get avrdude to restart the transaction without
      exitting and closing the libusb, causing the dragon to reset?
  (2) If I were to go through the hassle of patching avrdude to not need this
      spurious exit, would it be a dead-end because the dragon needs the reset
      in order to get itself back from DW into ISP?

Thanks for the info!  (avrdude rocks)


P.S. The (*) above is to mention that the call to free() in jtagmkII_teardown()
     dumps code for me in both 5.10 and SVN head, right as avrdude exits.

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