Ok, I don't want to sound rude, but did anyone actually *read* what I wrote?
I'll highlight the parts of lines in question this time, perhaps that
will help...
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);
}
OVER HERE ------------->>>>>--------------------------^^^^^^^^^^^^^^^^^
Either I'm missing something here, or someone needs to explain to me why
a test for AVR_HAVE_RAMPZ preceeds the use of AVR_HAVE_RAMPD in the code.
Shouldn't that last one also be RAMPZ ?
If not, why?
-Ian
On 17/12/2021 16:53, Bruce D. Lightner wrote:
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