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Re: [avr-gcc-list] >4.5.1 better than this at register-structure (xmega)

From: Weddington, Eric
Subject: Re: [avr-gcc-list] >4.5.1 better than this at register-structure (xmega) access?
Date: Wed, 10 Oct 2012 21:24:08 +0000

> -----Original Message-----
> From: address@hidden
> [mailto:address@hidden On
> Behalf Of Erik Walthinsen
> Sent: Wednesday, October 10, 2012 3:13 PM
> To: avr-gcc-list
> Subject: Re: [avr-gcc-list] >4.5.1 better than this at register-structure
> (xmega) access?
> On 10/10/2012 01:43 PM, Georg-Johann Lay wrote:
>  > Such a bug has never been reported to the GCC bug tracker.
> Well then, I guess I need to file one.  I just have no idea how to
> actually fix it, and no time to do so at this point ;-(
> > If nobody found it important enough to file a problem report for over 3
> > years (4.5 was released early 2009) I'd guess this is simply not an
> > important issue?
> It's not a bug per se but a missing optimization, so it's entirely
> possible nobody's cared enough to check.  I'm a) doing some extremely
> time-critical ISR routines, and b) trying to actually make use of the
> struct convenience.
> > There is PR50448 which is similar but different and fixed for 4.7.0.
> Yeah, doesn't look like the same issue at all.
> > Xmega is supported in avr-gcc since 4.7.0 (PR52261) so you obviously use
> > some private port with its own, private bug tracker.

> No, I'm using a version that matched the latest toolchain source I could
> get from Atmel at the time (6-12mo ago?) and took their patches
> including Xmega, which didn't include any more than the 64a1u, 128a1u,
> and 256a3bu.  I had to go through *all* the toolchain to add in the rest
> of the parts that are available from Digikey.

Johann is being pedantic. Atmel has their own set of patches, i.e. it *is* a 
private port, because those patches aren't fully submitted upstream yet.

> So, I guess I'll ask again: where do I actually get TODAY's toolchain?
> I keep reading about how Atmel takes forever to release the patches to
> the toolchain they ship, yet they now seem to be the "only" official
> toolchain, and nobody else appears to be actually maintaining patches
> separately.  Unless the GCC core is actually being kept up now and
> nobody bothered to mention it, but I just downloaded 4.7.2 and found the
> exact same set of parts missing.

I'm working on getting Atmel's patches upstream.

But specifically to your problem: I've had a latent concern about the xmega 
register definitions via structure layout. My concern is that the compiler 
would do exactly as you describe and always try to do an address/offset type of 
access to registers.

But as you said: Does it do that with recent versions? I'm afraid that no one 
yet knows.

Eric Weddington

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