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<a name="Pseudo-Instructions"></a>
<h4 class="subsection">9.5.4 Pseudo Instructions</h4>

<p>The only available pseudo-instruction <code>__gcc_isr</code> can be activated by
option <samp>-mgcc-isr</samp>.
</p>
<dl compact="compact">
<dt><code>__gcc_isr 1</code></dt>
<dd><p>Emit code chunk to be used in avr-gcc ISR prologue.
It will expand to at most six 1-word instructions, all optional:
push of <code>tmp_reg</code>, push of <code>SREG</code>,
push and clear of <code>zero_reg</code>, push of <var>Reg</var>.
</p>
</dd>
<dt><code>__gcc_isr 2</code></dt>
<dd><p>Emit code chunk to be used in an avr-gcc ISR epilogue.
It will expand to at most five 1-word instructions, all optional: 
pop of <var>Reg</var>, pop of <code>zero_reg</code>,
pop of <code>SREG</code>, pop of <code>tmp_reg</code>.
</p>
</dd>
<dt><code>__gcc_isr 0, <var>Reg</var></code></dt>
<dd><p>Finish avr-gcc ISR function.  Scan code since the last prologue
for usage of: <code>SREG</code>, <code>tmp_reg</code>, <code>zero_reg</code>.
Prologue chunk and epilogue chunks will be replaced by appropriate code
to save / restore <code>SREG</code>, <code>tmp_reg</code>, <code>zero_reg</code> and <var>Reg</var>.
</p>
</dd>
</dl>

<p>Example input:
</p>
<div class="example">
<pre class="example">__vector1:
    __gcc_isr 1
    lds r24, var
    inc r24
    sts var, r24
    __gcc_isr 2
    reti
    __gcc_isr 0, r24
</pre></div>

<p>Example output:
</p>
<div class="example">
<pre class="example">00000000 &lt;__vector1&gt;:
   0:   8f 93           push    r24
   2:   8f b7           in      r24, 0x3f
   4:   8f 93           push    r24
   6:   80 91 60 00     lds     r24, 0x0060     ; 0x800060 &lt;var&gt;
   a:   83 95           inc     r24
   c:   80 93 60 00     sts     0x0060, r24     ; 0x800060 &lt;var&gt;
  10:   8f 91           pop     r24
  12:   8f bf           out     0x3f, r24
  14:   8f 91           pop     r24
  16:   18 95           reti
</pre></div>


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