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<h1>crc16.h</h1><a href="crc16_8h.html">Go to the documentation of this file.</a><div class="fragment"><pre class="fragment"><a name="l00001"></a>00001 <span class="comment">/* Copyright (c) 2002, 2003, 2004 Marek Michalkiewicz</span>
<a name="l00002"></a>00002 <span class="comment"> Copyright (c) 2005, 2007 Joerg Wunsch</span>
<a name="l00003"></a>00003 <span class="comment"> Copyright (c) 2013 Dave Hylands</span>
<a name="l00004"></a>00004 <span class="comment"> Copyright (c) 2013 Frederic Nadeau</span>
<a name="l00005"></a>00005 <span class="comment"> All rights reserved.</span>
<a name="l00006"></a>00006 <span class="comment"></span>
<a name="l00007"></a>00007 <span class="comment"> Redistribution and use in source and binary forms, with or without</span>
<a name="l00008"></a>00008 <span class="comment"> modification, are permitted provided that the following conditions are met:</span>
<a name="l00009"></a>00009 <span class="comment"></span>
<a name="l00010"></a>00010 <span class="comment"> * Redistributions of source code must retain the above copyright</span>
<a name="l00011"></a>00011 <span class="comment"> notice, this list of conditions and the following disclaimer.</span>
<a name="l00012"></a>00012 <span class="comment"></span>
<a name="l00013"></a>00013 <span class="comment"> * Redistributions in binary form must reproduce the above copyright</span>
<a name="l00014"></a>00014 <span class="comment"> notice, this list of conditions and the following disclaimer in</span>
<a name="l00015"></a>00015 <span class="comment"> the documentation and/or other materials provided with the</span>
<a name="l00016"></a>00016 <span class="comment"> distribution.</span>
<a name="l00017"></a>00017 <span class="comment"></span>
<a name="l00018"></a>00018 <span class="comment"> * Neither the name of the copyright holders nor the names of</span>
<a name="l00019"></a>00019 <span class="comment"> contributors may be used to endorse or promote products derived</span>
<a name="l00020"></a>00020 <span class="comment"> from this software without specific prior written permission.</span>
<a name="l00021"></a>00021 <span class="comment"></span>
<a name="l00022"></a>00022 <span class="comment"> THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"</span>
<a name="l00023"></a>00023 <span class="comment"> AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE</span>
<a name="l00024"></a>00024 <span class="comment"> IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE</span>
<a name="l00025"></a>00025 <span class="comment"> ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE</span>
<a name="l00026"></a>00026 <span class="comment"> LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR</span>
<a name="l00027"></a>00027 <span class="comment"> CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF</span>
<a name="l00028"></a>00028 <span class="comment"> SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS</span>
<a name="l00029"></a>00029 <span class="comment"> INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN</span>
<a name="l00030"></a>00030 <span class="comment"> CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)</span>
<a name="l00031"></a>00031 <span class="comment"> ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE</span>
<a name="l00032"></a>00032 <span class="comment"> POSSIBILITY OF SUCH DAMAGE. */</span>
<a name="l00033"></a>00033
<a name="l00034"></a>00034 <span class="comment">/* $Id$ */</span>
<a name="l00035"></a>00035
<a name="l00036"></a>00036 <span class="preprocessor">#ifndef _UTIL_CRC16_H_</span>
<a name="l00037"></a>00037 <span class="preprocessor"></span><span class="preprocessor">#define _UTIL_CRC16_H_</span>
<a name="l00038"></a>00038 <span class="preprocessor"></span>
<a name="l00039"></a>00039 <span class="preprocessor">#include <<a class="code" href="stdint_8h.html">stdint.h</a>></span>
<a name="l00040"></a>00040 <span class="comment"></span>
<a name="l00041"></a>00041 <span class="comment">/** \file */</span><span class="comment"></span>
<a name="l00042"></a>00042 <span class="comment">/** \defgroup util_crc <util/crc16.h>: CRC Computations</span>
<a name="l00043"></a>00043 <span class="comment"> \code#include <util/crc16.h>\endcode</span>
<a name="l00044"></a>00044 <span class="comment"></span>
<a name="l00045"></a>00045 <span class="comment"> This header file provides a optimized inline functions for calculating</span>
<a name="l00046"></a>00046 <span class="comment"> cyclic redundancy checks (CRC) using common polynomials.</span>
<a name="l00047"></a>00047 <span class="comment"></span>
<a name="l00048"></a>00048 <span class="comment"> \par References:</span>
<a name="l00049"></a>00049 <span class="comment"></span>
<a name="l00050"></a>00050 <span class="comment"> \par</span>
<a name="l00051"></a>00051 <span class="comment"></span>
<a name="l00052"></a>00052 <span class="comment"> See the Dallas Semiconductor app note 27 for 8051 assembler example and</span>
<a name="l00053"></a>00053 <span class="comment"> general CRC optimization suggestions. The table on the last page of the</span>
<a name="l00054"></a>00054 <span class="comment"> app note is the key to understanding these implementations.</span>
<a name="l00055"></a>00055 <span class="comment"></span>
<a name="l00056"></a>00056 <span class="comment"> \par</span>
<a name="l00057"></a>00057 <span class="comment"></span>
<a name="l00058"></a>00058 <span class="comment"> Jack Crenshaw's "Implementing CRCs" article in the January 1992 isue of \e</span>
<a name="l00059"></a>00059 <span class="comment"> Embedded \e Systems \e Programming. This may be difficult to find, but it</span>
<a name="l00060"></a>00060 <span class="comment"> explains CRC's in very clear and concise terms. Well worth the effort to</span>
<a name="l00061"></a>00061 <span class="comment"> obtain a copy.</span>
<a name="l00062"></a>00062 <span class="comment"></span>
<a name="l00063"></a>00063 <span class="comment"> A typical application would look like:</span>
<a name="l00064"></a>00064 <span class="comment"></span>
<a name="l00065"></a>00065 <span class="comment"> \code</span>
<a name="l00066"></a>00066 <span class="comment"> // Dallas iButton test vector.</span>
<a name="l00067"></a>00067 <span class="comment"> uint8_t serno[] = { 0x02, 0x1c, 0xb8, 0x01, 0, 0, 0, 0xa2 };</span>
<a name="l00068"></a>00068 <span class="comment"></span>
<a name="l00069"></a>00069 <span class="comment"> int</span>
<a name="l00070"></a>00070 <span class="comment"> checkcrc(void)</span>
<a name="l00071"></a>00071 <span class="comment"> {</span>
<a name="l00072"></a>00072 <span class="comment"> uint8_t crc = 0, i;</span>
<a name="l00073"></a>00073 <span class="comment"></span>
<a name="l00074"></a>00074 <span class="comment"> for (i = 0; i < sizeof serno / sizeof serno[0]; i++)</span>
<a name="l00075"></a>00075 <span class="comment"> crc = _crc_ibutton_update(crc, serno[i]);</span>
<a name="l00076"></a>00076 <span class="comment"></span>
<a name="l00077"></a>00077 <span class="comment"> return crc; // must be 0</span>
<a name="l00078"></a>00078 <span class="comment"> }</span>
<a name="l00079"></a>00079 <span class="comment"> \endcode</span>
<a name="l00080"></a>00080 <span class="comment">*/</span>
<a name="l00081"></a>00081 <span class="comment"></span>
<a name="l00082"></a>00082 <span class="comment">/** \ingroup util_crc</span>
<a name="l00083"></a>00083 <span class="comment"> Optimized CRC-16 calculation.</span>
<a name="l00084"></a>00084 <span class="comment"></span>
<a name="l00085"></a>00085 <span class="comment"> Polynomial: x^16 + x^15 + x^2 + 1 (0xa001)<br></span>
<a name="l00086"></a>00086 <span class="comment"> Initial value: 0xffff</span>
<a name="l00087"></a>00087 <span class="comment"></span>
<a name="l00088"></a>00088 <span class="comment"> This CRC is normally used in disk-drive controllers.</span>
<a name="l00089"></a>00089 <span class="comment"></span>
<a name="l00090"></a>00090 <span class="comment"> The following is the equivalent functionality written in C.</span>
<a name="l00091"></a>00091 <span class="comment"></span>
<a name="l00092"></a>00092 <span class="comment"> \code</span>
<a name="l00093"></a>00093 <span class="comment"> uint16_t</span>
<a name="l00094"></a>00094 <span class="comment"> crc16_update(uint16_t crc, uint8_t a)</span>
<a name="l00095"></a>00095 <span class="comment"> {</span>
<a name="l00096"></a>00096 <span class="comment"> int i;</span>
<a name="l00097"></a>00097 <span class="comment"></span>
<a name="l00098"></a>00098 <span class="comment"> crc ^= a;</span>
<a name="l00099"></a>00099 <span class="comment"> for (i = 0; i < 8; ++i)</span>
<a name="l00100"></a>00100 <span class="comment"> {</span>
<a name="l00101"></a>00101 <span class="comment"> if (crc & 1)</span>
<a name="l00102"></a>00102 <span class="comment"> crc = (crc >> 1) ^ 0xA001;</span>
<a name="l00103"></a>00103 <span class="comment"> else</span>
<a name="l00104"></a>00104 <span class="comment"> crc = (crc >> 1);</span>
<a name="l00105"></a>00105 <span class="comment"> }</span>
<a name="l00106"></a>00106 <span class="comment"></span>
<a name="l00107"></a>00107 <span class="comment"> return crc;</span>
<a name="l00108"></a>00108 <span class="comment"> }</span>
<a name="l00109"></a>00109 <span class="comment"></span>
<a name="l00110"></a>00110 <span class="comment"> \endcode */</span>
<a name="l00111"></a>00111
<a name="l00112"></a>00112 <span class="keyword">static</span> __inline__ <a class="code" href="group__avr__stdint.html#ga1f1825b69244eb3ad2c7165ddc99c956">uint16_t</a>
<a name="l00113"></a><a class="code" href="group__util__crc.html#ga95371c87f25b0a2497d9cba13190847f">00113</a> <a class="code" href="group__util__crc.html#ga95371c87f25b0a2497d9cba13190847f">_crc16_update</a>(<a class="code" href="group__avr__stdint.html#ga1f1825b69244eb3ad2c7165ddc99c956">uint16_t</a> __crc, <a class="code" href="group__avr__stdint.html#gaba7bc1797add20fe3efdf37ced1182c5">uint8_t</a> __data)
<a name="l00114"></a>00114 {
<a name="l00115"></a>00115 <a class="code" href="group__avr__stdint.html#gaba7bc1797add20fe3efdf37ced1182c5">uint8_t</a> __tmp;
<a name="l00116"></a>00116 <a class="code" href="group__avr__stdint.html#ga1f1825b69244eb3ad2c7165ddc99c956">uint16_t</a> __ret;
<a name="l00117"></a>00117
<a name="l00118"></a>00118 __asm__ __volatile__ (
<a name="l00119"></a>00119 <span class="stringliteral">"eor %A0,%2"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00120"></a>00120 <span class="stringliteral">"mov %1,%A0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00121"></a>00121 <span class="stringliteral">"swap %1"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00122"></a>00122 <span class="stringliteral">"eor %1,%A0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00123"></a>00123 <span class="stringliteral">"mov __tmp_reg__,%1"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00124"></a>00124 <span class="stringliteral">"lsr %1"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00125"></a>00125 <span class="stringliteral">"lsr %1"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00126"></a>00126 <span class="stringliteral">"eor %1,__tmp_reg__"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00127"></a>00127 <span class="stringliteral">"mov __tmp_reg__,%1"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00128"></a>00128 <span class="stringliteral">"lsr %1"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00129"></a>00129 <span class="stringliteral">"eor %1,__tmp_reg__"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00130"></a>00130 <span class="stringliteral">"andi %1,0x07"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00131"></a>00131 <span class="stringliteral">"mov __tmp_reg__,%A0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00132"></a>00132 <span class="stringliteral">"mov %A0,%B0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00133"></a>00133 <span class="stringliteral">"lsr %1"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00134"></a>00134 <span class="stringliteral">"ror __tmp_reg__"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00135"></a>00135 <span class="stringliteral">"ror %1"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00136"></a>00136 <span class="stringliteral">"mov %B0,__tmp_reg__"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00137"></a>00137 <span class="stringliteral">"eor %A0,%1"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00138"></a>00138 <span class="stringliteral">"lsr __tmp_reg__"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00139"></a>00139 <span class="stringliteral">"ror %1"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00140"></a>00140 <span class="stringliteral">"eor %B0,__tmp_reg__"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00141"></a>00141 <span class="stringliteral">"eor %A0,%1"</span>
<a name="l00142"></a>00142 : <span class="stringliteral">"=r"</span> (__ret), <span class="stringliteral">"=d"</span> (__tmp)
<a name="l00143"></a>00143 : <span class="stringliteral">"r"</span> (__data), <span class="stringliteral">"0"</span> (__crc)
<a name="l00144"></a>00144 : <span class="stringliteral">"r0"</span>
<a name="l00145"></a>00145 );
<a name="l00146"></a>00146 <span class="keywordflow">return</span> __ret;
<a name="l00147"></a>00147 }
<a name="l00148"></a>00148 <span class="comment"></span>
<a name="l00149"></a>00149 <span class="comment">/** \ingroup util_crc</span>
<a name="l00150"></a>00150 <span class="comment"> Optimized CRC-XMODEM calculation.</span>
<a name="l00151"></a>00151 <span class="comment"></span>
<a name="l00152"></a>00152 <span class="comment"> Polynomial: x^16 + x^12 + x^5 + 1 (0x1021)<br></span>
<a name="l00153"></a>00153 <span class="comment"> Initial value: 0x0</span>
<a name="l00154"></a>00154 <span class="comment"></span>
<a name="l00155"></a>00155 <span class="comment"> This is the CRC used by the Xmodem-CRC protocol.</span>
<a name="l00156"></a>00156 <span class="comment"></span>
<a name="l00157"></a>00157 <span class="comment"> The following is the equivalent functionality written in C.</span>
<a name="l00158"></a>00158 <span class="comment"></span>
<a name="l00159"></a>00159 <span class="comment"> \code</span>
<a name="l00160"></a>00160 <span class="comment"> uint16_t</span>
<a name="l00161"></a>00161 <span class="comment"> crc_xmodem_update (uint16_t crc, uint8_t data)</span>
<a name="l00162"></a>00162 <span class="comment"> {</span>
<a name="l00163"></a>00163 <span class="comment"> int i;</span>
<a name="l00164"></a>00164 <span class="comment"></span>
<a name="l00165"></a>00165 <span class="comment"> crc = crc ^ ((uint16_t)data << 8);</span>
<a name="l00166"></a>00166 <span class="comment"> for (i=0; i<8; i++)</span>
<a name="l00167"></a>00167 <span class="comment"> {</span>
<a name="l00168"></a>00168 <span class="comment"> if (crc & 0x8000)</span>
<a name="l00169"></a>00169 <span class="comment"> crc = (crc << 1) ^ 0x1021;</span>
<a name="l00170"></a>00170 <span class="comment"> else</span>
<a name="l00171"></a>00171 <span class="comment"> crc <<= 1;</span>
<a name="l00172"></a>00172 <span class="comment"> }</span>
<a name="l00173"></a>00173 <span class="comment"></span>
<a name="l00174"></a>00174 <span class="comment"> return crc;</span>
<a name="l00175"></a>00175 <span class="comment"> }</span>
<a name="l00176"></a>00176 <span class="comment"> \endcode */</span>
<a name="l00177"></a>00177
<a name="l00178"></a>00178 <span class="keyword">static</span> __inline__ <a class="code" href="group__avr__stdint.html#ga1f1825b69244eb3ad2c7165ddc99c956">uint16_t</a>
<a name="l00179"></a><a class="code" href="group__util__crc.html#gaca726c22a1900f9bad52594c8846115f">00179</a> <a class="code" href="group__util__crc.html#gaca726c22a1900f9bad52594c8846115f">_crc_xmodem_update</a>(<a class="code" href="group__avr__stdint.html#ga1f1825b69244eb3ad2c7165ddc99c956">uint16_t</a> __crc, <a class="code" href="group__avr__stdint.html#gaba7bc1797add20fe3efdf37ced1182c5">uint8_t</a> __data)
<a name="l00180"></a>00180 {
<a name="l00181"></a>00181 <a class="code" href="group__avr__stdint.html#ga1f1825b69244eb3ad2c7165ddc99c956">uint16_t</a> __ret; <span class="comment">/* %B0:%A0 (alias for __crc) */</span>
<a name="l00182"></a>00182 <a class="code" href="group__avr__stdint.html#gaba7bc1797add20fe3efdf37ced1182c5">uint8_t</a> __tmp1; <span class="comment">/* %1 */</span>
<a name="l00183"></a>00183 <a class="code" href="group__avr__stdint.html#gaba7bc1797add20fe3efdf37ced1182c5">uint8_t</a> __tmp2; <span class="comment">/* %2 */</span>
<a name="l00184"></a>00184 <span class="comment">/* %3 __data */</span>
<a name="l00185"></a>00185
<a name="l00186"></a>00186 __asm__ __volatile__ (
<a name="l00187"></a>00187 <span class="stringliteral">"eor %B0,%3"</span> <span class="stringliteral">"\n\t"</span> <span class="comment">/* crc.hi ^ data */</span>
<a name="l00188"></a>00188 <span class="stringliteral">"mov __tmp_reg__,%B0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00189"></a>00189 <span class="stringliteral">"swap __tmp_reg__"</span> <span class="stringliteral">"\n\t"</span> <span class="comment">/* swap(crc.hi ^ data) */</span>
<a name="l00190"></a>00190
<a name="l00191"></a>00191 <span class="comment">/* Calculate the ret.lo of the CRC. */</span>
<a name="l00192"></a>00192 <span class="stringliteral">"mov %1,__tmp_reg__"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00193"></a>00193 <span class="stringliteral">"andi %1,0x0f"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00194"></a>00194 <span class="stringliteral">"eor %1,%B0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00195"></a>00195 <span class="stringliteral">"mov %2,%B0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00196"></a>00196 <span class="stringliteral">"eor %2,__tmp_reg__"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00197"></a>00197 <span class="stringliteral">"lsl %2"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00198"></a>00198 <span class="stringliteral">"andi %2,0xe0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00199"></a>00199 <span class="stringliteral">"eor %1,%2"</span> <span class="stringliteral">"\n\t"</span> <span class="comment">/* __tmp1 is now ret.lo. */</span>
<a name="l00200"></a>00200
<a name="l00201"></a>00201 <span class="comment">/* Calculate the ret.hi of the CRC. */</span>
<a name="l00202"></a>00202 <span class="stringliteral">"mov %2,__tmp_reg__"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00203"></a>00203 <span class="stringliteral">"eor %2,%B0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00204"></a>00204 <span class="stringliteral">"andi %2,0xf0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00205"></a>00205 <span class="stringliteral">"lsr %2"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00206"></a>00206 <span class="stringliteral">"mov __tmp_reg__,%B0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00207"></a>00207 <span class="stringliteral">"lsl __tmp_reg__"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00208"></a>00208 <span class="stringliteral">"rol %2"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00209"></a>00209 <span class="stringliteral">"lsr %B0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00210"></a>00210 <span class="stringliteral">"lsr %B0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00211"></a>00211 <span class="stringliteral">"lsr %B0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00212"></a>00212 <span class="stringliteral">"andi %B0,0x1f"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00213"></a>00213 <span class="stringliteral">"eor %B0,%2"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00214"></a>00214 <span class="stringliteral">"eor %B0,%A0"</span> <span class="stringliteral">"\n\t"</span> <span class="comment">/* ret.hi is now ready. */</span>
<a name="l00215"></a>00215 <span class="stringliteral">"mov %A0,%1"</span> <span class="stringliteral">"\n\t"</span> <span class="comment">/* ret.lo is now ready. */</span>
<a name="l00216"></a>00216 : <span class="stringliteral">"=d"</span> (__ret), <span class="stringliteral">"=d"</span> (__tmp1), <span class="stringliteral">"=d"</span> (__tmp2)
<a name="l00217"></a>00217 : <span class="stringliteral">"r"</span> (__data), <span class="stringliteral">"0"</span> (__crc)
<a name="l00218"></a>00218 : <span class="stringliteral">"r0"</span>
<a name="l00219"></a>00219 );
<a name="l00220"></a>00220 <span class="keywordflow">return</span> __ret;
<a name="l00221"></a>00221 }
<a name="l00222"></a>00222 <span class="comment"></span>
<a name="l00223"></a>00223 <span class="comment">/** \ingroup util_crc</span>
<a name="l00224"></a>00224 <span class="comment"> Optimized CRC-CCITT calculation.</span>
<a name="l00225"></a>00225 <span class="comment"></span>
<a name="l00226"></a>00226 <span class="comment"> Polynomial: x^16 + x^12 + x^5 + 1 (0x8408)<br></span>
<a name="l00227"></a>00227 <span class="comment"> Initial value: 0xffff</span>
<a name="l00228"></a>00228 <span class="comment"></span>
<a name="l00229"></a>00229 <span class="comment"> This is the CRC used by PPP and IrDA.</span>
<a name="l00230"></a>00230 <span class="comment"></span>
<a name="l00231"></a>00231 <span class="comment"> See RFC1171 (PPP protocol) and IrDA IrLAP 1.1</span>
<a name="l00232"></a>00232 <span class="comment"></span>
<a name="l00233"></a>00233 <span class="comment"> \note Although the CCITT polynomial is the same as that used by the Xmodem</span>
<a name="l00234"></a>00234 <span class="comment"> protocol, they are quite different. The difference is in how the bits are</span>
<a name="l00235"></a>00235 <span class="comment"> shifted through the alorgithm. Xmodem shifts the MSB of the CRC and the</span>
<a name="l00236"></a>00236 <span class="comment"> input first, while CCITT shifts the LSB of the CRC and the input first.</span>
<a name="l00237"></a>00237 <span class="comment"></span>
<a name="l00238"></a>00238 <span class="comment"> The following is the equivalent functionality written in C.</span>
<a name="l00239"></a>00239 <span class="comment"></span>
<a name="l00240"></a>00240 <span class="comment"> \code</span>
<a name="l00241"></a>00241 <span class="comment"> uint16_t</span>
<a name="l00242"></a>00242 <span class="comment"> crc_ccitt_update (uint16_t crc, uint8_t data)</span>
<a name="l00243"></a>00243 <span class="comment"> {</span>
<a name="l00244"></a>00244 <span class="comment"> data ^= lo8 (crc);</span>
<a name="l00245"></a>00245 <span class="comment"> data ^= data << 4;</span>
<a name="l00246"></a>00246 <span class="comment"></span>
<a name="l00247"></a>00247 <span class="comment"> return ((((uint16_t)data << 8) | hi8 (crc)) ^ (uint8_t)(data >> 4) </span>
<a name="l00248"></a>00248 <span class="comment"> ^ ((uint16_t)data << 3));</span>
<a name="l00249"></a>00249 <span class="comment"> }</span>
<a name="l00250"></a>00250 <span class="comment"> \endcode */</span>
<a name="l00251"></a>00251
<a name="l00252"></a>00252 <span class="keyword">static</span> __inline__ <a class="code" href="group__avr__stdint.html#ga1f1825b69244eb3ad2c7165ddc99c956">uint16_t</a>
<a name="l00253"></a><a class="code" href="group__util__crc.html#ga1c1d3ad875310cbc58000e24d981ad20">00253</a> <a class="code" href="group__util__crc.html#ga1c1d3ad875310cbc58000e24d981ad20">_crc_ccitt_update</a> (<a class="code" href="group__avr__stdint.html#ga1f1825b69244eb3ad2c7165ddc99c956">uint16_t</a> __crc, <a class="code" href="group__avr__stdint.html#gaba7bc1797add20fe3efdf37ced1182c5">uint8_t</a> __data)
<a name="l00254"></a>00254 {
<a name="l00255"></a>00255 <a class="code" href="group__avr__stdint.html#ga1f1825b69244eb3ad2c7165ddc99c956">uint16_t</a> __ret;
<a name="l00256"></a>00256
<a name="l00257"></a>00257 __asm__ __volatile__ (
<a name="l00258"></a>00258 <span class="stringliteral">"eor %A0,%1"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00259"></a>00259
<a name="l00260"></a>00260 <span class="stringliteral">"mov __tmp_reg__,%A0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00261"></a>00261 <span class="stringliteral">"swap %A0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00262"></a>00262 <span class="stringliteral">"andi %A0,0xf0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00263"></a>00263 <span class="stringliteral">"eor %A0,__tmp_reg__"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00264"></a>00264
<a name="l00265"></a>00265 <span class="stringliteral">"mov __tmp_reg__,%B0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00266"></a>00266
<a name="l00267"></a>00267 <span class="stringliteral">"mov %B0,%A0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00268"></a>00268
<a name="l00269"></a>00269 <span class="stringliteral">"swap %A0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00270"></a>00270 <span class="stringliteral">"andi %A0,0x0f"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00271"></a>00271 <span class="stringliteral">"eor __tmp_reg__,%A0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00272"></a>00272
<a name="l00273"></a>00273 <span class="stringliteral">"lsr %A0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00274"></a>00274 <span class="stringliteral">"eor %B0,%A0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00275"></a>00275
<a name="l00276"></a>00276 <span class="stringliteral">"eor %A0,%B0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00277"></a>00277 <span class="stringliteral">"lsl %A0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00278"></a>00278 <span class="stringliteral">"lsl %A0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00279"></a>00279 <span class="stringliteral">"lsl %A0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00280"></a>00280 <span class="stringliteral">"eor %A0,__tmp_reg__"</span>
<a name="l00281"></a>00281
<a name="l00282"></a>00282 : <span class="stringliteral">"=d"</span> (__ret)
<a name="l00283"></a>00283 : <span class="stringliteral">"r"</span> (__data), <span class="stringliteral">"0"</span> (__crc)
<a name="l00284"></a>00284 : <span class="stringliteral">"r0"</span>
<a name="l00285"></a>00285 );
<a name="l00286"></a>00286 <span class="keywordflow">return</span> __ret;
<a name="l00287"></a>00287 }
<a name="l00288"></a>00288 <span class="comment"></span>
<a name="l00289"></a>00289 <span class="comment">/** \ingroup util_crc</span>
<a name="l00290"></a>00290 <span class="comment"> Optimized Dallas (now Maxim) iButton 8-bit CRC calculation.</span>
<a name="l00291"></a>00291 <span class="comment"></span>
<a name="l00292"></a>00292 <span class="comment"> Polynomial: x^8 + x^5 + x^4 + 1 (0x8C)<br></span>
<a name="l00293"></a>00293 <span class="comment"> Initial value: 0x0</span>
<a name="l00294"></a>00294 <span class="comment"></span>
<a name="l00295"></a>00295 <span class="comment"> See http://www.maxim-ic.com/appnotes.cfm/appnote_number/27</span>
<a name="l00296"></a>00296 <span class="comment"></span>
<a name="l00297"></a>00297 <span class="comment"> The following is the equivalent functionality written in C.</span>
<a name="l00298"></a>00298 <span class="comment"></span>
<a name="l00299"></a>00299 <span class="comment"> \code</span>
<a name="l00300"></a>00300 <span class="comment"> uint8_t</span>
<a name="l00301"></a>00301 <span class="comment"> _crc_ibutton_update(uint8_t crc, uint8_t data)</span>
<a name="l00302"></a>00302 <span class="comment"> {</span>
<a name="l00303"></a>00303 <span class="comment"> uint8_t i;</span>
<a name="l00304"></a>00304 <span class="comment"></span>
<a name="l00305"></a>00305 <span class="comment"> crc = crc ^ data;</span>
<a name="l00306"></a>00306 <span class="comment"> for (i = 0; i < 8; i++)</span>
<a name="l00307"></a>00307 <span class="comment"> {</span>
<a name="l00308"></a>00308 <span class="comment"> if (crc & 0x01)</span>
<a name="l00309"></a>00309 <span class="comment"> crc = (crc >> 1) ^ 0x8C;</span>
<a name="l00310"></a>00310 <span class="comment"> else</span>
<a name="l00311"></a>00311 <span class="comment"> crc >>= 1;</span>
<a name="l00312"></a>00312 <span class="comment"> }</span>
<a name="l00313"></a>00313 <span class="comment"></span>
<a name="l00314"></a>00314 <span class="comment"> return crc;</span>
<a name="l00315"></a>00315 <span class="comment"> }</span>
<a name="l00316"></a>00316 <span class="comment"> \endcode</span>
<a name="l00317"></a>00317 <span class="comment">*/</span>
<a name="l00318"></a>00318
<a name="l00319"></a>00319 <span class="keyword">static</span> __inline__ <a class="code" href="group__avr__stdint.html#gaba7bc1797add20fe3efdf37ced1182c5">uint8_t</a>
<a name="l00320"></a><a class="code" href="group__util__crc.html#ga37b2f691ebbd917e36e40b096f78d996">00320</a> <a class="code" href="group__util__crc.html#ga37b2f691ebbd917e36e40b096f78d996">_crc_ibutton_update</a>(<a class="code" href="group__avr__stdint.html#gaba7bc1797add20fe3efdf37ced1182c5">uint8_t</a> __crc, <a class="code" href="group__avr__stdint.html#gaba7bc1797add20fe3efdf37ced1182c5">uint8_t</a> __data)
<a name="l00321"></a>00321 {
<a name="l00322"></a>00322 <a class="code" href="group__avr__stdint.html#gaba7bc1797add20fe3efdf37ced1182c5">uint8_t</a> __i, __pattern;
<a name="l00323"></a>00323 __asm__ __volatile__ (
<a name="l00324"></a>00324 <span class="stringliteral">" eor %0, %4"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00325"></a>00325 <span class="stringliteral">" ldi %1, 8"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00326"></a>00326 <span class="stringliteral">" ldi %2, 0x8C"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00327"></a>00327 <span class="stringliteral">"1: lsr %0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00328"></a>00328 <span class="stringliteral">" brcc 2f"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00329"></a>00329 <span class="stringliteral">" eor %0, %2"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00330"></a>00330 <span class="stringliteral">"2: dec %1"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00331"></a>00331 <span class="stringliteral">" brne 1b"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00332"></a>00332 : <span class="stringliteral">"=r"</span> (__crc), <span class="stringliteral">"=d"</span> (__i), <span class="stringliteral">"=d"</span> (__pattern)
<a name="l00333"></a>00333 : <span class="stringliteral">"0"</span> (__crc), <span class="stringliteral">"r"</span> (__data));
<a name="l00334"></a>00334 <span class="keywordflow">return</span> __crc;
<a name="l00335"></a>00335 }
<a name="l00336"></a>00336 <span class="comment"></span>
<a name="l00337"></a>00337 <span class="comment">/** \ingroup util_crc</span>
<a name="l00338"></a>00338 <span class="comment"> Optimized CRC-8-CCITT calculation.</span>
<a name="l00339"></a>00339 <span class="comment"></span>
<a name="l00340"></a>00340 <span class="comment"> Polynomial: x^8 + x^2 + x + 1 (0xE0)<br></span>
<a name="l00341"></a>00341 <span class="comment"> </span>
<a name="l00342"></a>00342 <span class="comment"> For use with simple CRC-8<br></span>
<a name="l00343"></a>00343 <span class="comment"> Initial value: 0x0</span>
<a name="l00344"></a>00344 <span class="comment"> </span>
<a name="l00345"></a>00345 <span class="comment"> For use with CRC-8-ROHC<br></span>
<a name="l00346"></a>00346 <span class="comment"> Initial value: 0xff<br></span>
<a name="l00347"></a>00347 <span class="comment"> Reference: http://tools.ietf.org/html/rfc3095#section-5.9.1</span>
<a name="l00348"></a>00348 <span class="comment"> </span>
<a name="l00349"></a>00349 <span class="comment"> For use with CRC-8-ATM/ITU<br></span>
<a name="l00350"></a>00350 <span class="comment"> Initial value: 0xff<br></span>
<a name="l00351"></a>00351 <span class="comment"> Final XOR value: 0x55<br></span>
<a name="l00352"></a>00352 <span class="comment"> Reference: http://www.itu.int/rec/T-REC-I.432.1-199902-I/en</span>
<a name="l00353"></a>00353 <span class="comment"> </span>
<a name="l00354"></a>00354 <span class="comment"> The C equivalent has been originally written by Dave Hylands.</span>
<a name="l00355"></a>00355 <span class="comment"> Assembly code is based on _crc_ibutton_update optimization.</span>
<a name="l00356"></a>00356 <span class="comment"></span>
<a name="l00357"></a>00357 <span class="comment"> The following is the equivalent functionality written in C.</span>
<a name="l00358"></a>00358 <span class="comment"></span>
<a name="l00359"></a>00359 <span class="comment"> \code</span>
<a name="l00360"></a>00360 <span class="comment"> uint8_t</span>
<a name="l00361"></a>00361 <span class="comment"> _crc8_ccitt_update (uint8_t inCrc, uint8_t inData)</span>
<a name="l00362"></a>00362 <span class="comment"> {</span>
<a name="l00363"></a>00363 <span class="comment"> uint8_t i;</span>
<a name="l00364"></a>00364 <span class="comment"> uint8_t data;</span>
<a name="l00365"></a>00365 <span class="comment"></span>
<a name="l00366"></a>00366 <span class="comment"> data = inCrc ^ inData;</span>
<a name="l00367"></a>00367 <span class="comment"></span>
<a name="l00368"></a>00368 <span class="comment"> for ( i = 0; i < 8; i++ )</span>
<a name="l00369"></a>00369 <span class="comment"> {</span>
<a name="l00370"></a>00370 <span class="comment"> if (( data & 0x80 ) != 0 )</span>
<a name="l00371"></a>00371 <span class="comment"> {</span>
<a name="l00372"></a>00372 <span class="comment"> data <<= 1;</span>
<a name="l00373"></a>00373 <span class="comment"> data ^= 0x07;</span>
<a name="l00374"></a>00374 <span class="comment"> }</span>
<a name="l00375"></a>00375 <span class="comment"> else</span>
<a name="l00376"></a>00376 <span class="comment"> {</span>
<a name="l00377"></a>00377 <span class="comment"> data <<= 1;</span>
<a name="l00378"></a>00378 <span class="comment"> }</span>
<a name="l00379"></a>00379 <span class="comment"> }</span>
<a name="l00380"></a>00380 <span class="comment"> return data;</span>
<a name="l00381"></a>00381 <span class="comment"> }</span>
<a name="l00382"></a>00382 <span class="comment"> \endcode</span>
<a name="l00383"></a>00383 <span class="comment">*/</span>
<a name="l00384"></a>00384
<a name="l00385"></a>00385 <span class="keyword">static</span> __inline__ <a class="code" href="group__avr__stdint.html#gaba7bc1797add20fe3efdf37ced1182c5">uint8_t</a>
<a name="l00386"></a><a class="code" href="group__util__crc.html#gab27eaaef6d7fd096bd7d57bf3f9ba083">00386</a> <a class="code" href="group__util__crc.html#gab27eaaef6d7fd096bd7d57bf3f9ba083">_crc8_ccitt_update</a>(<a class="code" href="group__avr__stdint.html#gaba7bc1797add20fe3efdf37ced1182c5">uint8_t</a> __crc, <a class="code" href="group__avr__stdint.html#gaba7bc1797add20fe3efdf37ced1182c5">uint8_t</a> __data)
<a name="l00387"></a>00387 {
<a name="l00388"></a>00388 <a class="code" href="group__avr__stdint.html#gaba7bc1797add20fe3efdf37ced1182c5">uint8_t</a> __i, __pattern;
<a name="l00389"></a>00389 __asm__ __volatile__ (
<a name="l00390"></a>00390 <span class="stringliteral">" eor %0, %4"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00391"></a>00391 <span class="stringliteral">" ldi %1, 8"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00392"></a>00392 <span class="stringliteral">" ldi %2, 0x07"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00393"></a>00393 <span class="stringliteral">"1: lsl %0"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00394"></a>00394 <span class="stringliteral">" brcc 2f"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00395"></a>00395 <span class="stringliteral">" eor %0, %2"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00396"></a>00396 <span class="stringliteral">"2: dec %1"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00397"></a>00397 <span class="stringliteral">" brne 1b"</span> <span class="stringliteral">"\n\t"</span>
<a name="l00398"></a>00398 : <span class="stringliteral">"=r"</span> (__crc), <span class="stringliteral">"=d"</span> (__i), <span class="stringliteral">"=d"</span> (__pattern)
<a name="l00399"></a>00399 : <span class="stringliteral">"0"</span> (__crc), <span class="stringliteral">"r"</span> (__data));
<a name="l00400"></a>00400 <span class="keywordflow">return</span> __crc;
<a name="l00401"></a>00401 }
<a name="l00402"></a>00402
<a name="l00403"></a>00403 <span class="preprocessor">#endif </span><span class="comment">/* _UTIL_CRC16_H_ */</span>
</pre></div></div>
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