source: arduino-1-6-7/trunk/fuentes/arduino-ide-amd64/hardware/tools/avr/avr/include/util/delay_basic.h @ 4837

Last change on this file since 4837 was 4837, checked in by daduve, 2 years ago

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1/* Copyright (c) 2002, Marek Michalkiewicz
2   Copyright (c) 2007 Joerg Wunsch
3   All rights reserved.
4
5   Redistribution and use in source and binary forms, with or without
6   modification, are permitted provided that the following conditions are met:
7
8   * Redistributions of source code must retain the above copyright
9     notice, this list of conditions and the following disclaimer.
10
11   * Redistributions in binary form must reproduce the above copyright
12     notice, this list of conditions and the following disclaimer in
13     the documentation and/or other materials provided with the
14     distribution.
15
16   * Neither the name of the copyright holders nor the names of
17     contributors may be used to endorse or promote products derived
18     from this software without specific prior written permission.
19
20  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
21  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
24  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
25  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
26  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
27  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
28  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
29  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
30  POSSIBILITY OF SUCH DAMAGE. */
31
32/* $Id$ */
33
34#ifndef _UTIL_DELAY_BASIC_H_
35#define _UTIL_DELAY_BASIC_H_ 1
36
37#include <inttypes.h>
38
39#if !defined(__DOXYGEN__)
40static __inline__ void _delay_loop_1(uint8_t __count) __attribute__((__always_inline__));
41static __inline__ void _delay_loop_2(uint16_t __count) __attribute__((__always_inline__));
42#endif
43
44/** \file */
45/** \defgroup util_delay_basic <util/delay_basic.h>: Basic busy-wait delay loops
46    \code
47    #include <util/delay_basic.h>
48    \endcode
49
50    The functions in this header file implement simple delay loops
51    that perform a busy-waiting.  They are typically used to
52    facilitate short delays in the program execution.  They are
53    implemented as count-down loops with a well-known CPU cycle
54    count per loop iteration.  As such, no other processing can
55    occur simultaneously.  It should be kept in mind that the
56    functions described here do not disable interrupts.
57
58    In general, for long delays, the use of hardware timers is
59    much preferrable, as they free the CPU, and allow for
60    concurrent processing of other events while the timer is
61    running.  However, in particular for very short delays, the
62    overhead of setting up a hardware timer is too much compared
63    to the overall delay time.
64
65    Two inline functions are provided for the actual delay algorithms.
66
67*/
68
69/** \ingroup util_delay_basic
70
71    Delay loop using an 8-bit counter \c __count, so up to 256
72    iterations are possible.  (The value 256 would have to be passed
73    as 0.)  The loop executes three CPU cycles per iteration, not
74    including the overhead the compiler needs to setup the counter
75    register.
76
77    Thus, at a CPU speed of 1 MHz, delays of up to 768 microseconds
78    can be achieved.
79*/
80void
81_delay_loop_1(uint8_t __count)
82{
83        __asm__ volatile (
84                "1: dec %0" "\n\t"
85                "brne 1b"
86                : "=r" (__count)
87                : "0" (__count)
88        );
89}
90
91/** \ingroup util_delay_basic
92
93    Delay loop using a 16-bit counter \c __count, so up to 65536
94    iterations are possible.  (The value 65536 would have to be
95    passed as 0.)  The loop executes four CPU cycles per iteration,
96    not including the overhead the compiler requires to setup the
97    counter register pair.
98
99    Thus, at a CPU speed of 1 MHz, delays of up to about 262.1
100    milliseconds can be achieved.
101 */
102void
103_delay_loop_2(uint16_t __count)
104{
105        __asm__ volatile (
106                "1: sbiw %0,1" "\n\t"
107                "brne 1b"
108                : "=w" (__count)
109                : "0" (__count)
110        );
111}
112
113#endif /* _UTIL_DELAY_BASIC_H_ */
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