Re: GCC bug?

[Bruce D. Lightner]

Ian,

I apologize if I was being obtuse! :-)

The AVR_HAVE_RAMPD #define tells the routine "emit_push_sfr()" to save the RAMPD register, but only if the third parameter to the call is non-zero.  The constant AVR_HAVE_RAMPD will be non-zero if the AVR micro-architecture supports a RAMPD register.

That's why you see the code you reported.  Much older versions of avr-gcc have "emit_push_sfr()" source code with one less parameter (i.e., no AVR_HAVE_RAMPD reference) because the RAMPD "paging" register is a relatively "new" AVR feature.

Best regards,

Bruce

---

On 12/17/2021 5:39 AM, Ian Molton wrote:

> I think you misunderstood me;
>
> I know this is where the compiler will save RAMPZ where needed.
>
> So why is it referencing RAMP *D* ?
>
> On 17/12/2021 00:50, Bruce D. Lightner wrote:
> > Ian,
> >
> > Just from a purely AVR architecture point of view, the AVR_HAVE_RAMPD
> > #define indicates that the AVR chip in question supports the "RAMP"
> > paging register, described as follows:
> >
> >    *RAMPD*
> >    Register concatenated with the Z-register enabling direct addressing
> > of the whole data space on MCUs
> >    with more than 64KB data space.
> >
> > Eventually the originally tiny AVR chips' addressable memory got so big
> > that we needed a "paging" register.  (That's a repeating theme with
> > every 8-bit/16-bit microcontroller family.)
> >
> > So the "RAMPD" register needs to be saved along with the X, Y and Z
> > "special function" registers, if it is present.
> >
> > Best regards,
> >
> > Bruce
> >
> > ------------------------------------------------------------------------
> > On 12/16/2021 3:46 PM, Ian Molton wrote:
> > > Browsing the GCC source, I found this in gcc/config/avr/avr.c
> > >
> > >  if (AVR_HAVE_RAMPZ
> > >           && TEST_HARD_REG_BIT (set, REG_Z)
> > >           && TEST_HARD_REG_BIT (set, REG_Z + 1))
> > >         {
> > >           emit_push_sfr (rampz_rtx, false /* frame */, AVR_HAVE_RAMPD,
> > > treg);
> > >         }
> > >
> > >
> > > I wont pretend to fully understand this part of the compiler, but that
> > > AVR_HAVE_RAMPD looks shady to me?
> > >
> > > Anyone with deeper knowledge want to have a look?
> > >
> > > -Ian
> > >
> > >         
> >         
> >       
>

--
Bruce D. Lightner
Lightner Engineering
La Jolla, CA
Email: lightner@lightner.net
URL: http://www.lightner.net/lightner/bruce/