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Re: [avr-libc-dev] [Bug #3327] I read from phorum that outb() is deprec

From: Joerg Wunsch
Subject: Re: [avr-libc-dev] [Bug #3327] I read from phorum that outb() is deprecated? But still can found a note from library "Use outb
Date: Mon, 5 May 2003 11:07:05 +0200
User-agent: Mutt/1.2.5i

As Theodore A. Roth wrote:

> Ok. Those arguments are compelling enough for me. I am now in
> agreement as to the deprecation of (and eventual removal of) the
> outb() and friends macros.

Well, we don't need to completely ban outb(), but the docs should
point out that it's effectively the same as the direct assignment
form.  In particular it doesn't guarantee an OUT instruction will be
used.  It uses the same MMIO paradigm internally, and with -O0 will
come out as (expensive) MMIO as well.  For the upper registers on the
ATmega128, it can only translate into MMIO anyway, and for anything
else, the optimizer will turn it into an OUT instruction.

I think there's a discussion about the MMIO vs. separate IO space
instructions somewhere in the docs.  This should probably be extended
to mention that the direct assigment form is preferable since it is
more in line with other AVR compilers.  I'd volunteer to write a FAQ
entry "Why is outb() deprecated?" that summarizes this, and points to
the more detailed IO explanation.  It could also discuss the need for
a separate HAL in projects where cross-platform portability is an
issue (just a sentence or two).

> Joerg,
> Thanks for talking the time to write the detailed discussion.

Thanks for appreciating that it took me some time to compose this
message. ;-)  It caused a bit of delay in the discussion since i
wasn't in the mood to think deeper about all this, and write it down.

J"org Wunsch                                           Unix support engineer
address@hidden        http://www.interface-systems.de/~j/

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