Re: GCC bug?
"Bruce D. Lightner" <[email protected]> Fri, 17 Dec 2021 08:53:09 -0800
| Newsgroups | gmane.comp.hardware.avr.gcc |
|---|---|
| Message-ID | <[email protected]> |
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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: [email protected]
URL: http://www.lightner.net/lightner/bruce/
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<div class="moz-cite-prefix">Ian,<br>
<br>
I apologize if I was being obtuse! :-)<br>
<br>
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.<br>
<br>
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.<br>
<br>
Best regards,<br>
<br>
Bruce<br>
<br>
<hr width="100%" size="2">On 12/17/2021 5:39 AM, Ian Molton wrote:<br>
</div>
<blockquote type="cite"
cite="mid:[email protected]">
<pre class="moz-quote-pre" wrap="">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:
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">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:
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">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
</pre>
</blockquote>
<br>
</blockquote>
</blockquote>
<br>
<div class="moz-signature">-- <br>
<span style="font-size:9pt;font-family:sans-serif;"> <b>Bruce D.
Lightner</b><br>
<b>Lightner Engineering</b><br>
La Jolla, CA<br>
Email: <a class="moz-txt-link-abbreviated" href="mailto:[email protected]">[email protected]</a><br>
URL: <a class="moz-txt-link-freetext" href="http://www.lightner.net/lightner/bruce/">http://www.lightner.net/lightner/bruce/</a><br>
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