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Re: [avr-gcc-list] memory layout for bootloader

From: Joerg Wunsch
Subject: Re: [avr-gcc-list] memory layout for bootloader
Date: Thu, 16 Jun 2005 07:17:57 +0200 (MET DST)

Torsten Mohr <address@hidden> wrote:

> Can i really DISABLE SPI programming by fuse bit SPIEN?

You can.  But read the text carefully: you cannot do that while using
ISP programming. ;-)  So it's not a shoot-into-your-foot (SIYF) fuse.

The only real SIYF fuse they ever invented is the reset disable fuse
on the ATmega8.

There are semi-SIYF fuses when you select a clock option that will
result in the device no longer being clocked, but you can usually
always resurrect them by supplying an external clock.  Some people who
don't even own a simple pulse generator occasionally even program a
second AVR for that purpose, and use that one's clock output as clock
supply for the device to resurrect. ;-)

On the debugWire-capable devices, the DWEN fuse is most likely also a
semi-SIYF fuse: debugWire uses a kind of 1-wire protocol across the
/RESET-pin, so this pin no longer works as a normal reset.  The only
way back then is to use a JTAG ICE mkII, and talk debugWire across it
in order to turn it off again.  Hmm, perhaps we could persuade Atmel
to at least publish a bit sequence you need on dW that will resurrect
an indadvertently programmed DWEN fuse without a JTAG ICE...

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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