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Re: [avr-chat] Using avrdude on linux to enter and leave dW

From: Markus Baertschi
Subject: Re: [avr-chat] Using avrdude on linux to enter and leave dW
Date: Mon, 18 Apr 2011 09:21:23 +0200

So, if I understand this correctly:
- Fuses can not be programmed in dW mode, but you can get out of dW mode into ISP mode temporarily (to unprogram fuses vie ISP)
- Avrdude will attempt to connect in dW mode and to switch to ISP when the initial connect via ISP fails. So I can use avrdude -P usb -c dragon_isp -p t85 -v -U hfuse:w:0xDF:m to clear the DWEN fuse even is the chip is in dW mode (DWEN fuse programmed).

My ISP connection is functional and there is nothing connected to reset except the dragon.

Thanks  Markus

On Mon, Apr 18, 2011 at 08:14, Joerg Wunsch <address@hidden> wrote:
Markus Baertschi <address@hidden> wrote:

> I did presume that using this I can go back to ISP:

>> avrdude -P usb -c dragon_dw -p t85 -v -U hfuse:w:0xDF:m

No.  dragon_dw cannot reprogram fuses, as debugWIRE mode cannot handle
that.  You have to use dragon_isp again.  It will fail in the first
attempt, but then issue the sequence to get out of debugWIRE.  After
this, you have to re-issue the (ISP!) command, and it's supposed to

Of course, nothing mandates you'd have to reprogram the fuses at this
point at all: debugWIRE mode is just left temporarily in order to
assign the /RESET pin to the ISP algorithm again.  This state lasts
until the next power-cycle, at which point the DWEN fuse will be
evaluated again.  So, if you intend to continue debugging, you could
as well just use ISP mode to download new firmware (my experience says
it's often faster and more reliable than within debugWIRE mode), and
then just power-cycle to start a new debugging session.

Obviously, your debugWIRE mode must be functional in order to get out
of debugWIRE.  If there are hardware issues that make debugWIRE mode
not work (too much capacitive load at /RESET etc.), all this wouldn't
work at all.
cheers, J"org               .-.-.   --... ...--   -.. .  DL8DTL

http://www.sax.de/~joerg/                        NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)

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