Re: [avr-chat] Question about reading & writing in one command...

[Joerg Wunsch]

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Mike Meyer <address@hidden> wrote:

> Is there some reason that avrdude doesn't do any requested write
> operations before doing the erase for the flash? Or is it just that
> nobody has asked for it yet?

It's more a matter that nobody *implemented* it.

Right now, AVRDUDE first passes the entire commandline arguments.  It
then goes ahead, and analyzes all -U options to see whether there's
one that would want to write to "flash" (or in the SVN version, for
Xmega parts, to "application").  If so, and if auto-erase is not
forbidden, it then erases the part.  Likewise, if there's a -e option
around anywhere on the commandline, it also issues an erase cycle.
Only then, it starts processing the -U (update) options.

And no, that's not so easy to avoid as you might think.  For non-Xmega
devices, the erase operation is performed as a chip erase, which can
potentially also erase the EEPROM.  Suppose we would generally defer
that operation until the actual flash write -U option is being
processed, it could then lead to a previously performed EEPROM write
to be clobbered.

The only chance I'd see to avoid further side effects would be to add
another -U suboption "e" (for "erase").  As all -U options are
processed in order, this would specify the exact timing of when the
erase happens.  (Presence of at least one -U ...:e: option could then
be used as an indication to not schedule the default auto-erase before
processing the -U options.)  This would have the added bonus that it
also easily solves the missing feature where we are currently not able
to specify an erase operation for individual Xmega flash regions (boot
vs. application).  So perhaps I'm going to implement it that way
before releasing version 6.0.

-- 
cheers, J"org               .-.-.   --... ...--   -.. .  DL8DTL

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