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cpufunc.h
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1 /* Copyright (c) 2010, Joerg Wunsch
2  All rights reserved.
3 
4  Redistribution and use in source and binary forms, with or without
5  modification, are permitted provided that the following conditions are met:
6 
7  * Redistributions of source code must retain the above copyright
8  notice, this list of conditions and the following disclaimer.
9 
10  * Redistributions in binary form must reproduce the above copyright
11  notice, this list of conditions and the following disclaimer in
12  the documentation and/or other materials provided with the
13  distribution.
14 
15  * Neither the name of the copyright holders nor the names of
16  contributors may be used to endorse or promote products derived
17  from this software without specific prior written permission.
18 
19  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
20  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
21  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
22  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
23  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
24  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
25  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
26  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
27  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
28  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
29  POSSIBILITY OF SUCH DAMAGE. */
30 
31 /* $Id: cpufunc_8h_source.html,v 1.1.1.5 2014/08/13 06:29:33 joerg_wunsch Exp $ */
32 
33 /* avr/cpufunc.h - Special CPU functions */
34 
35 #ifndef _AVR_CPUFUNC_H_
36 #define _AVR_CPUFUNC_H_ 1
37 
38 /** \file */
39 /** \defgroup avr_cpufunc <avr/cpufunc.h>: Special AVR CPU functions
40  \code #include <avr/cpufunc.h> \endcode
41 
42  This header file contains macros that access special functions of
43  the AVR CPU which do not fit into any of the other header files.
44 
45 */
46 
47 #if defined(__DOXYGEN__)
48 /**
49  \ingroup avr_cpufunc
50  \def _NOP
51 
52  Execute a <i>no operation</i> (NOP) CPU instruction. This
53  should not be used to implement delays, better use the functions
54  from <util/delay_basic.h> or <util/delay.h> for this. For
55  debugging purposes, a NOP can be useful to have an instruction that
56  is guaranteed to be not optimized away by the compiler, so it can
57  always become a breakpoint in the debugger.
58 */
59 #define _NOP()
60 #else /* real code */
61 #define _NOP() __asm__ __volatile__("nop")
62 #endif /* __DOXYGEN__ */
63 
64 #if defined(__DOXYGEN__)
65 /**
66  \ingroup avr_cpufunc
67  \def _MemoryBarrier
68 
69  Implement a read/write <i>memory barrier</i>. A memory
70  barrier instructs the compiler to not cache any memory data in
71  registers beyond the barrier. This can sometimes be more effective
72  than blocking certain optimizations by declaring some object with a
73  \c volatile qualifier.
74 
75  See \ref optim_code_reorder for things to be taken into account
76  with respect to compiler optimizations.
77 */
78 #define _MemoryBarrier()
79 #else /* real code */
80 #define _MemoryBarrier() __asm__ __volatile__("":::"memory")
81 #endif /* __DOXYGEN__ */
82 
83 #endif /* _AVR_CPUFUNC_H_ */

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