visus
/
toolchain-gcc-arm-embedded


			
							<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- Copyright (C) 1988-2020 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Funding Free Software", the Front-Cover
Texts being (a) (see below), and with the Back-Cover Texts being (b)
(see below).  A copy of the license is included in the section entitled
"GNU Free Documentation License".

(a) The FSF's Front-Cover Text is:

A GNU Manual

(b) The FSF's Back-Cover Text is:

You have freedom to copy and modify this GNU Manual, like GNU
     software.  Copies published by the Free Software Foundation raise
     funds for GNU development. -->
<!-- Created by GNU Texinfo 6.5, http://www.gnu.org/software/texinfo/ -->
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>AVR Built-in Functions (Using the GNU Compiler Collection (GCC))</title>

<meta name="description" content="AVR Built-in Functions (Using the GNU Compiler Collection (GCC))">
<meta name="keywords" content="AVR Built-in Functions (Using the GNU Compiler Collection (GCC))">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<link href="index.html#Top" rel="start" title="Top">
<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="Target-Builtins.html#Target-Builtins" rel="up" title="Target Builtins">
<link href="Blackfin-Built_002din-Functions.html#Blackfin-Built_002din-Functions" rel="next" title="Blackfin Built-in Functions">
<link href="ARM-ARMv8_002dM-Security-Extensions.html#ARM-ARMv8_002dM-Security-Extensions" rel="prev" title="ARM ARMv8-M Security Extensions">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.indentedblock {margin-right: 0em}
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
div.smalllisp {margin-left: 3.2em}
kbd {font-style: oblique}
pre.display {font-family: inherit}
pre.format {font-family: inherit}
pre.menu-comment {font-family: serif}
pre.menu-preformatted {font-family: serif}
pre.smalldisplay {font-family: inherit; font-size: smaller}
pre.smallexample {font-size: smaller}
pre.smallformat {font-family: inherit; font-size: smaller}
pre.smalllisp {font-size: smaller}
span.nolinebreak {white-space: nowrap}
span.roman {font-family: initial; font-weight: normal}
span.sansserif {font-family: sans-serif; font-weight: normal}
ul.no-bullet {list-style: none}
-->
</style>


</head>

<body lang="en">
<a name="AVR-Built_002din-Functions"></a>
<div class="header">
<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>
</div>
<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>
<dl compact="compact">
<dt><code>void __builtin_avr_nop (void)</code></dt>
<dt><code>void __builtin_avr_sei (void)</code></dt>
<dt><code>void __builtin_avr_cli (void)</code></dt>
<dt><code>void __builtin_avr_sleep (void)</code></dt>
<dt><code>void __builtin_avr_wdr (void)</code></dt>
<dt><code>unsigned char __builtin_avr_swap (unsigned char)</code></dt>
<dt><code>unsigned int __builtin_avr_fmul (unsigned char, unsigned char)</code></dt>
<dt><code>int __builtin_avr_fmuls (char, char)</code></dt>
<dt><code>int __builtin_avr_fmulsu (char, unsigned char)</code></dt>
<dd><p>These 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>
</dd>
<dt><code>void __builtin_avr_delay_cycles (unsigned long ticks)</code></dt>
<dd><p>Delay execution for <var>ticks</var> cycles. Note that this
built-in does not take into account the effect of interrupts that
might increase delay time. <var>ticks</var> must be a compile-time
integer constant; delays with a variable number of cycles are not supported.
</p>
</dd>
<dt><code>char __builtin_avr_flash_segment (const __memx void*)</code></dt>
<dd><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>
</dd>
<dt><code>uint8_t __builtin_avr_insert_bits (uint32_t map, uint8_t bits, uint8_t val)</code></dt>
<dd><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>

</dd>
<dt><code>void __builtin_avr_nops (unsigned count)</code></dt>
<dd><p>Insert <var>count</var> <code>NOP</code> instructions.
The number of instructions must be a compile-time integer constant.
</p>
</dd>
</dl>

<p>There are many more AVR-specific built-in functions that are used to
implement the ISO/IEC TR 18037 &ldquo;Embedded C&rdquo; fixed-point functions of
section 7.18a.6.  You don&rsquo;t need to use these built-ins directly.
Instead, use the declarations as supplied by the <code>stdfix.h</code> header
with GNU-C99:
</p>
<div class="smallexample">
<pre class="smallexample">#include &lt;stdfix.h&gt;

// Re-interpret the bit representation of unsigned 16-bit
// integer <var>uval</var> as Q-format 0.16 value.
unsigned fract get_bits (uint_ur_t uval)
{
    return urbits (uval);
}
</pre></div>

<hr>
<div class="header">
<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>
</div>


</body>
</html>