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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.h 2158 2010-06-10 15:48:28Z joerg_wunsch $ */
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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