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134 lines
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134 lines
6.4 KiB
HTML
4 years ago
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<html lang="en">
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<title>AVR Built-in Functions - Using the GNU Compiler Collection (GCC)</title>
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<meta name="description" content="Using the GNU Compiler Collection (GCC)">
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<link rel="up" href="Target-Builtins.html#Target-Builtins" title="Target Builtins">
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<link rel="prev" href="ARM-Floating-Point-Status-and-Control-Intrinsics.html#ARM-Floating-Point-Status-and-Control-Intrinsics" title="ARM Floating Point Status and Control Intrinsics">
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<link rel="next" href="Blackfin-Built_002din-Functions.html#Blackfin-Built_002din-Functions" title="Blackfin Built-in Functions">
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Copyright (C) 1988-2015 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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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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</head>
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<body>
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<div class="node">
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<a name="AVR-Built-in-Functions"></a>
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<a name="AVR-Built_002din-Functions"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Blackfin-Built_002din-Functions.html#Blackfin-Built_002din-Functions">Blackfin Built-in Functions</a>,
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Previous: <a rel="previous" accesskey="p" href="ARM-Floating-Point-Status-and-Control-Intrinsics.html#ARM-Floating-Point-Status-and-Control-Intrinsics">ARM Floating Point Status and Control Intrinsics</a>,
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Up: <a rel="up" accesskey="u" href="Target-Builtins.html#Target-Builtins">Target Builtins</a>
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<hr>
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</div>
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<h4 class="subsection">6.58.9 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>The following 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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<pre class="smallexample"> void __builtin_avr_nop (void)
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void __builtin_avr_sei (void)
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void __builtin_avr_cli (void)
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void __builtin_avr_sleep (void)
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void __builtin_avr_wdr (void)
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unsigned char __builtin_avr_swap (unsigned char)
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unsigned int __builtin_avr_fmul (unsigned char, unsigned char)
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int __builtin_avr_fmuls (char, char)
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int __builtin_avr_fmulsu (char, unsigned char)
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</pre>
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<p>In order to delay execution for a specific number of cycles, GCC
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implements
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<pre class="smallexample"> void __builtin_avr_delay_cycles (unsigned long ticks)
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</pre>
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<p class="noindent"><code>ticks</code> is the number of ticks to delay execution. 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. <code>ticks</code> 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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<pre class="smallexample"> char __builtin_avr_flash_segment (const __memx void*)
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</pre>
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<p class="noindent">This built-in takes a byte address to the 24-bit
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<a href="AVR-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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<pre class="smallexample"> unsigned char __builtin_avr_insert_bits (unsigned long map, unsigned char bits, unsigned char val)
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</pre>
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<p class="noindent">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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<ol type=1 start=1>
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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>If X is in the range 0<small class="dots">...</small>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>If X is in the range 8<small class="dots">...</small><code>0xe</code>,
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then the <var>n</var>-th result bit is undefined.
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</ol>
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<p class="noindent">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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<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>
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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>
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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>
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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>
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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>
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</body></html>
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