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delay_basic.h
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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: delay_basic.h 2143 2010-06-08 21:19:51Z joerg_wunsch $ */
33
34 #ifndef _UTIL_DELAY_BASIC_H_
35 #define _UTIL_DELAY_BASIC_H_ 1
36
37 #include <inttypes.h>
38
39 #if !defined(__DOXYGEN__)
40 static inline void _delay_loop_1(uint8_t __count) __attribute__((always_inline));
41 static 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 */
80 void
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 */
102 void
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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