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196 lines
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196 lines
8.8 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<!-- Copyright (C) 1988-2018 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>AVR Built-in Functions (Using the GNU Compiler Collection (GCC))</title>
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<meta name="description" content="AVR Built-in Functions (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="AVR Built-in Functions (Using the GNU Compiler Collection (GCC))">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Target-Builtins.html#Target-Builtins" rel="up" title="Target Builtins">
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<link href="Blackfin-Built_002din-Functions.html#Blackfin-Built_002din-Functions" rel="next" title="Blackfin Built-in Functions">
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<link href="ARM-ARMv8_002dM-Security-Extensions.html#ARM-ARMv8_002dM-Security-Extensions" rel="prev" title="ARM ARMv8-M Security Extensions">
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</head>
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<body lang="en">
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<a name="AVR-Built_002din-Functions"></a>
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<div class="header">
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<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> [<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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</div>
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<hr>
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<a name="AVR-Built_002din-Functions-1"></a>
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<h4 class="subsection">6.59.10 AVR Built-in Functions</h4>
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<p>For each built-in function for AVR, there is an equally named,
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uppercase built-in macro defined. That way users can easily query if
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or if not a specific built-in is implemented or not. For example, if
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<code>__builtin_avr_nop</code> is available the macro
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<code>__BUILTIN_AVR_NOP</code> is defined to <code>1</code> and undefined otherwise.
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</p>
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<dl compact="compact">
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<dt><code>void __builtin_avr_nop (void)</code></dt>
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<dt><code>void __builtin_avr_sei (void)</code></dt>
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<dt><code>void __builtin_avr_cli (void)</code></dt>
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<dt><code>void __builtin_avr_sleep (void)</code></dt>
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<dt><code>void __builtin_avr_wdr (void)</code></dt>
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<dt><code>unsigned char __builtin_avr_swap (unsigned char)</code></dt>
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<dt><code>unsigned int __builtin_avr_fmul (unsigned char, unsigned char)</code></dt>
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<dt><code>int __builtin_avr_fmuls (char, char)</code></dt>
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<dt><code>int __builtin_avr_fmulsu (char, unsigned char)</code></dt>
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<dd><p>These built-in functions map to the respective machine
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instruction, i.e. <code>nop</code>, <code>sei</code>, <code>cli</code>, <code>sleep</code>,
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<code>wdr</code>, <code>swap</code>, <code>fmul</code>, <code>fmuls</code>
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resp. <code>fmulsu</code>. The three <code>fmul*</code> built-ins are implemented
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as library call if no hardware multiplier is available.
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</p>
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</dd>
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<dt><code>void __builtin_avr_delay_cycles (unsigned long ticks)</code></dt>
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<dd><p>Delay execution for <var>ticks</var> cycles. Note that this
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built-in does not take into account the effect of interrupts that
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might increase delay time. <var>ticks</var> must be a compile-time
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integer constant; delays with a variable number of cycles are not supported.
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</p>
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</dd>
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<dt><code>char __builtin_avr_flash_segment (const __memx void*)</code></dt>
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<dd><p>This built-in takes a byte address to the 24-bit
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<a href="Named-Address-Spaces.html#AVR-Named-Address-Spaces">address space</a> <code>__memx</code> and returns
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the number of the flash segment (the 64 KiB chunk) where the address
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points to. Counting starts at <code>0</code>.
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If the address does not point to flash memory, return <code>-1</code>.
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</p>
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</dd>
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<dt><code>uint8_t __builtin_avr_insert_bits (uint32_t map, uint8_t bits, uint8_t val)</code></dt>
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<dd><p>Insert bits from <var>bits</var> into <var>val</var> and return the resulting
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value. The nibbles of <var>map</var> determine how the insertion is
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performed: Let <var>X</var> be the <var>n</var>-th nibble of <var>map</var>
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</p><ol>
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<li> If <var>X</var> is <code>0xf</code>,
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then the <var>n</var>-th bit of <var>val</var> is returned unaltered.
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</li><li> If X is in the range 0…7,
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then the <var>n</var>-th result bit is set to the <var>X</var>-th bit of <var>bits</var>
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</li><li> If X is in the range 8…<code>0xe</code>,
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then the <var>n</var>-th result bit is undefined.
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</li></ol>
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<p>One typical use case for this built-in is adjusting input and
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output values to non-contiguous port layouts. Some examples:
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</p>
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<div class="smallexample">
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<pre class="smallexample">// same as val, bits is unused
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__builtin_avr_insert_bits (0xffffffff, bits, val)
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</pre></div>
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<div class="smallexample">
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<pre class="smallexample">// same as bits, val is unused
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__builtin_avr_insert_bits (0x76543210, bits, val)
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</pre></div>
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<div class="smallexample">
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<pre class="smallexample">// same as rotating bits by 4
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__builtin_avr_insert_bits (0x32107654, bits, 0)
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</pre></div>
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<div class="smallexample">
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<pre class="smallexample">// high nibble of result is the high nibble of val
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// low nibble of result is the low nibble of bits
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__builtin_avr_insert_bits (0xffff3210, bits, val)
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</pre></div>
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<div class="smallexample">
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<pre class="smallexample">// reverse the bit order of bits
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__builtin_avr_insert_bits (0x01234567, bits, 0)
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</pre></div>
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</dd>
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<dt><code>void __builtin_avr_nops (unsigned count)</code></dt>
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<dd><p>Insert <var>count</var> <code>NOP</code> instructions.
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The number of instructions must be a compile-time integer constant.
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</p>
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</dd>
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</dl>
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<p>There are many more AVR-specific built-in functions that are used to
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implement the ISO/IEC TR 18037 “Embedded C” fixed-point functions of
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section 7.18a.6. You don’t need to use these built-ins directly.
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Instead, use the declarations as supplied by the <code>stdfix.h</code> header
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with GNU-C99:
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</p>
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<div class="smallexample">
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<pre class="smallexample">#include <stdfix.h>
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// Re-interpret the bit representation of unsigned 16-bit
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// integer <var>uval</var> as Q-format 0.16 value.
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unsigned fract get_bits (uint_ur_t uval)
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{
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return urbits (uval);
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}
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</pre></div>
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<hr>
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<div class="header">
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<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> [<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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</div>
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