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<title>Using the GNU Compiler Collection (GCC): AVR Built-in Functions</title>

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<a name="AVR-Built_002din-Functions"></a>
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<p>
Next: <a href="Blackfin-Built_002din-Functions.html#Blackfin-Built_002din-Functions" accesskey="n" rel="next">Blackfin Built-in Functions</a>, Previous: <a href="ARM-ARMv8_002dM-Security-Extensions.html#ARM-ARMv8_002dM-Security-Extensions" accesskey="p" rel="prev">ARM ARMv8-M Security Extensions</a>, Up: <a href="Target-Builtins.html#Target-Builtins" accesskey="u" rel="up">Target Builtins</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="AVR-Built_002din-Functions-1"></a>
<h4 class="subsection">6.60.10 AVR Built-in Functions</h4>

<p>For each built-in function for AVR, there is an equally named,
uppercase built-in macro defined. That way users can easily query if
or if not a specific built-in is implemented or not. For example, if
<code>__builtin_avr_nop</code> is available the macro
<code>__BUILTIN_AVR_NOP</code> is defined to <code>1</code> and undefined otherwise.
</p>
<p>The following built-in functions map to the respective machine
instruction, i.e. <code>nop</code>, <code>sei</code>, <code>cli</code>, <code>sleep</code>,
<code>wdr</code>, <code>swap</code>, <code>fmul</code>, <code>fmuls</code>
resp. <code>fmulsu</code>. The three <code>fmul*</code> built-ins are implemented
as library call if no hardware multiplier is available.
</p>
<div class="smallexample">
<pre class="smallexample">void __builtin_avr_nop (void)
void __builtin_avr_sei (void)
void __builtin_avr_cli (void)
void __builtin_avr_sleep (void)
void __builtin_avr_wdr (void)
unsigned char __builtin_avr_swap (unsigned char)
unsigned int __builtin_avr_fmul (unsigned char, unsigned char)
int __builtin_avr_fmuls (char, char)
int __builtin_avr_fmulsu (char, unsigned char)
</pre></div>

<p>In order to delay execution for a specific number of cycles, GCC
implements
</p><div class="smallexample">
<pre class="smallexample">void __builtin_avr_delay_cycles (unsigned long ticks)
</pre></div>

<p><code>ticks</code> is the number of ticks to delay execution. Note that this
built-in does not take into account the effect of interrupts that
might increase delay time. <code>ticks</code> must be a compile-time
integer constant; delays with a variable number of cycles are not supported.
</p>
<div class="smallexample">
<pre class="smallexample">char __builtin_avr_flash_segment (const __memx void*)
</pre></div>

<p>This built-in takes a byte address to the 24-bit
<a href="Named-Address-Spaces.html#AVR-Named-Address-Spaces">address space</a> <code>__memx</code> and returns
the number of the flash segment (the 64 KiB chunk) where the address
points to.  Counting starts at <code>0</code>.
If the address does not point to flash memory, return <code>-1</code>.
</p>
<div class="smallexample">
<pre class="smallexample">unsigned char __builtin_avr_insert_bits (unsigned long map,
                                         unsigned char bits,
                                         unsigned char val)
</pre></div>

<p>Insert bits from <var>bits</var> into <var>val</var> and return the resulting
value. The nibbles of <var>map</var> determine how the insertion is
performed: Let <var>X</var> be the <var>n</var>-th nibble of <var>map</var>
</p><ol>
<li> If <var>X</var> is <code>0xf</code>,
then the <var>n</var>-th bit of <var>val</var> is returned unaltered.

</li><li> If X is in the range 0&hellip;7,
then the <var>n</var>-th result bit is set to the <var>X</var>-th bit of <var>bits</var>

</li><li> If X is in the range 8&hellip;<code>0xe</code>,
then the <var>n</var>-th result bit is undefined.
</li></ol>

<p>One typical use case for this built-in is adjusting input and
output values to non-contiguous port layouts. Some examples:
</p>
<div class="smallexample">
<pre class="smallexample">// same as val, bits is unused
__builtin_avr_insert_bits (0xffffffff, bits, val)
</pre></div>

<div class="smallexample">
<pre class="smallexample">// same as bits, val is unused
__builtin_avr_insert_bits (0x76543210, bits, val)
</pre></div>

<div class="smallexample">
<pre class="smallexample">// same as rotating bits by 4
__builtin_avr_insert_bits (0x32107654, bits, 0)
</pre></div>

<div class="smallexample">
<pre class="smallexample">// high nibble of result is the high nibble of val
// low nibble of result is the low nibble of bits
__builtin_avr_insert_bits (0xffff3210, bits, val)
</pre></div>

<div class="smallexample">
<pre class="smallexample">// reverse the bit order of bits
__builtin_avr_insert_bits (0x01234567, bits, 0)
</pre></div>

<div class="smallexample">
<pre class="smallexample">void __builtin_avr_nops (unsigned count)
</pre></div>

<p>Insert <code>count</code> <code>NOP</code> instructions.
The number of instructions must be a compile-time integer constant.
</p>
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Next: <a href="Blackfin-Built_002din-Functions.html#Blackfin-Built_002din-Functions" accesskey="n" rel="next">Blackfin Built-in Functions</a>, Previous: <a href="ARM-ARMv8_002dM-Security-Extensions.html#ARM-ARMv8_002dM-Security-Extensions" accesskey="p" rel="prev">ARM ARMv8-M Security Extensions</a>, Up: <a href="Target-Builtins.html#Target-Builtins" accesskey="u" rel="up">Target Builtins</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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