source: arduino-1-6-7/trunk/fuentes/arduino-ide-amd64/hardware/tools/avr/avr/include/util/setbaud.h @ 46

Last change on this file since 46 was 46, checked in by jrpelegrina, 4 years ago

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1/* Copyright (c) 2007  Cliff Lawson
2   Copyright (c) 2007  Carlos Lamas
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/**
35   \file
36*/
37
38/**
39   \defgroup util_setbaud <util/setbaud.h>: Helper macros for baud rate calculations
40   \code
41   #define F_CPU 11059200
42   #define BAUD 38400
43   #include <util/setbaud.h>
44   \endcode
45
46   This header file requires that on entry values are already defined
47   for F_CPU and BAUD.  In addition, the macro BAUD_TOL will define
48   the baud rate tolerance (in percent) that is acceptable during
49   the calculations.  The value of BAUD_TOL will default to 2 %.
50
51   This header file defines macros suitable to setup the UART baud
52   rate prescaler registers of an AVR.  All calculations are done
53   using the C preprocessor.  Including this header file causes no
54   other side effects so it is possible to include this file more than
55   once (supposedly, with different values for the BAUD parameter),
56   possibly even within the same function.
57
58   Assuming that the requested BAUD is valid for the given F_CPU then
59   the macro UBRR_VALUE is set to the required prescaler value.  Two
60   additional macros are provided for the low and high bytes of the
61   prescaler, respectively: UBRRL_VALUE is set to the lower byte of
62   the UBRR_VALUE and UBRRH_VALUE is set to the upper byte.  An
63   additional macro USE_2X will be defined.  Its value is set to 1 if
64   the desired BAUD rate within the given tolerance could only be
65   achieved by setting the U2X bit in the UART configuration.  It will
66   be defined to 0 if U2X is not needed.
67
68   Example usage:
69
70   \code
71   #include <avr/io.h>
72
73   #define F_CPU 4000000
74
75   static void
76   uart_9600(void)
77   {
78   #define BAUD 9600
79   #include <util/setbaud.h>
80   UBRRH = UBRRH_VALUE;
81   UBRRL = UBRRL_VALUE;
82   #if USE_2X
83   UCSRA |= (1 << U2X);
84   #else
85   UCSRA &= ~(1 << U2X);
86   #endif
87   }
88
89   static void
90   uart_38400(void)
91   {
92   #undef BAUD  // avoid compiler warning
93   #define BAUD 38400
94   #include <util/setbaud.h>
95   UBRRH = UBRRH_VALUE;
96   UBRRL = UBRRL_VALUE;
97   #if USE_2X
98   UCSRA |= (1 << U2X);
99   #else
100   UCSRA &= ~(1 << U2X);
101   #endif
102   }
103   \endcode
104
105   In this example, two functions are defined to setup the UART
106   to run at 9600 Bd, and 38400 Bd, respectively.  Using a CPU
107   clock of 4 MHz, 9600 Bd can be achieved with an acceptable
108   tolerance without setting U2X (prescaler 25), while 38400 Bd
109   require U2X to be set (prescaler 12).
110*/
111
112#ifndef F_CPU
113#  error "setbaud.h requires F_CPU to be defined"
114#endif
115
116#ifndef BAUD
117#  error "setbaud.h requires BAUD to be defined"
118#endif
119
120#if !(F_CPU)
121#  error "F_CPU must be a constant value"
122#endif
123
124#if !(BAUD)
125#  error "BAUD must be a constant value"
126#endif
127
128#if defined(__DOXYGEN__)
129/**
130   \def BAUD_TOL
131   \ingroup util_setbaud
132
133   Input and output macro for <util/setbaud.h>
134
135   Define the acceptable baud rate tolerance in percent.  If not set
136   on entry, it will be set to its default value of 2.
137*/
138#define BAUD_TOL 2
139
140/**
141   \def UBRR_VALUE
142   \ingroup util_setbaud
143
144   Output macro from <util/setbaud.h>
145
146   Contains the calculated baud rate prescaler value for the UBRR
147   register.
148*/
149#define UBRR_VALUE
150
151/**
152   \def UBRRL_VALUE
153   \ingroup util_setbaud
154
155   Output macro from <util/setbaud.h>
156
157   Contains the lower byte of the calculated prescaler value
158   (UBRR_VALUE).
159*/
160#define UBRRL_VALUE
161
162/**
163   \def UBRRH_VALUE
164   \ingroup util_setbaud
165
166   Output macro from <util/setbaud.h>
167
168   Contains the upper byte of the calculated prescaler value
169   (UBRR_VALUE).
170*/
171#define UBRRH_VALUE
172
173/**
174   \def USE_2X
175   \ingroup util_setbaud
176
177   Output bacro from <util/setbaud.h>
178
179   Contains the value 1 if the desired baud rate tolerance could only
180   be achieved by setting the U2X bit in the UART configuration.
181   Contains 0 otherwise.
182*/
183#define USE_2X 0
184
185#else /* !__DOXYGEN__ */
186
187#undef USE_2X
188
189/* Baud rate tolerance is 2 % unless previously defined */
190#ifndef BAUD_TOL
191#  define BAUD_TOL 2
192#endif
193
194#ifdef __ASSEMBLER__
195#define UBRR_VALUE (((F_CPU) + 8 * (BAUD)) / (16 * (BAUD)) -1)
196#else
197#define UBRR_VALUE (((F_CPU) + 8UL * (BAUD)) / (16UL * (BAUD)) -1UL)
198#endif
199
200#if 100 * (F_CPU) > \
201  (16 * ((UBRR_VALUE) + 1)) * (100 * (BAUD) + (BAUD) * (BAUD_TOL))
202#  define USE_2X 1
203#elif 100 * (F_CPU) < \
204  (16 * ((UBRR_VALUE) + 1)) * (100 * (BAUD) - (BAUD) * (BAUD_TOL))
205#  define USE_2X 1
206#else
207#  define USE_2X 0
208#endif
209
210#if USE_2X
211/* U2X required, recalculate */
212#undef UBRR_VALUE
213
214#ifdef __ASSEMBLER__
215#define UBRR_VALUE (((F_CPU) + 4 * (BAUD)) / (8 * (BAUD)) -1)
216#else
217#define UBRR_VALUE (((F_CPU) + 4UL * (BAUD)) / (8UL * (BAUD)) -1UL)
218#endif
219
220#if 100 * (F_CPU) > \
221  (8 * ((UBRR_VALUE) + 1)) * (100 * (BAUD) + (BAUD) * (BAUD_TOL))
222#  warning "Baud rate achieved is higher than allowed"
223#endif
224
225#if 100 * (F_CPU) < \
226  (8 * ((UBRR_VALUE) + 1)) * (100 * (BAUD) - (BAUD) * (BAUD_TOL))
227#  warning "Baud rate achieved is lower than allowed"
228#endif
229
230#endif /* USE_U2X */
231
232#ifdef UBRR_VALUE
233   /* Check for overflow */
234#  if UBRR_VALUE >= (1 << 12)
235#    warning "UBRR value overflow"
236#  endif
237
238#  define UBRRL_VALUE (UBRR_VALUE & 0xff)
239#  define UBRRH_VALUE (UBRR_VALUE >> 8)
240#endif
241
242#endif /* __DOXYGEN__ */
243/* end of util/setbaud.h */
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