Documentation/DocBook/librs.tmpl

   1 <?xml version="1.0" encoding="UTF-8"?>
   2 <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
   3         "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
   4
   5 <book id="Reed-Solomon-Library-Guide">
   6  <bookinfo>
   7   <title>Reed-Solomon Library Programming Interface</title>
   8
   9   <authorgroup>
  10    <author>
  11     <firstname>Thomas</firstname>
  12     <surname>Gleixner</surname>
  13     <affiliation>
  14      <address>
  15       <email>tglx@linutronix.de</email>
  16      </address>
  17     </affiliation>
  18    </author>
  19   </authorgroup>
  20
  21   <copyright>
  22    <year>2004</year>
  23    <holder>Thomas Gleixner</holder>
  24   </copyright>
  25
  26   <legalnotice>
  27    <para>
  28      This documentation is free software; you can redistribute
  29      it and/or modify it under the terms of the GNU General Public
  30      License version 2 as published by the Free Software Foundation.
  31    </para>
  32
  33    <para>
  34      This program is distributed in the hope that it will be
  35      useful, but WITHOUT ANY WARRANTY; without even the implied
  36      warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  37      See the GNU General Public License for more details.
  38    </para>
  39
  40    <para>
  41      You should have received a copy of the GNU General Public
  42      License along with this program; if not, write to the Free
  43      Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
  44      MA 02111-1307 USA
  45    </para>
  46
  47    <para>
  48      For more details see the file COPYING in the source
  49      distribution of Linux.
  50    </para>
  51   </legalnotice>
  52  </bookinfo>
  53
  54 <toc></toc>
  55
  56   <chapter id="intro">
  57       <title>Introduction</title>
  58   <para>
  59         The generic Reed-Solomon Library provides encoding, decoding
  60         and error correction functions.
  61   </para>
  62   <para>
  63         Reed-Solomon codes are used in communication and storage
  64         applications to ensure data integrity.
  65   </para>
  66   <para>
  67         This documentation is provided for developers who want to utilize
  68         the functions provided by the library.
  69   </para>
  70   </chapter>
  71
  72   <chapter id="bugs">
  73      <title>Known Bugs And Assumptions</title>
  74   <para>
  75         None.
  76   </para>
  77   </chapter>
  78
  79   <chapter id="usage">
  80         <title>Usage</title>
  81         <para>
  82                 This chapter provides examples how to use the library.
  83         </para>
  84         <sect1>
  85                 <title>Initializing</title>
  86                 <para>
  87                         The init function init_rs returns a pointer to a
  88                         rs decoder structure, which holds the necessary
  89                         information for encoding, decoding and error correction
  90                         with the given polynomial. It either uses an existing
  91                         matching decoder or creates a new one. On creation all
  92                         the lookup tables for fast en/decoding are created.
  93                         The function may take a while, so make sure not to
  94                         call it in critical code paths.
  95                 </para>
  96                 <programlisting>
  97 /* the Reed Solomon control structure */
  98 static struct rs_control *rs_decoder;
  99
 100 /* Symbolsize is 10 (bits)
 101  * Primitve polynomial is x^10+x^3+1
 102  * first consecutive root is 0
 103  * primitve element to generate roots = 1
 104  * generator polinomial degree (number of roots) = 6
 105  */
 106 rs_decoder = init_rs (10, 0x409, 0, 1, 6);
 107                 </programlisting>
 108         </sect1>
 109         <sect1>
 110                 <title>Encoding</title>
 111                 <para>
 112                         The encoder calculates the Reed-Solomon code over
 113                         the given data length and stores the result in
 114                         the parity buffer. Note that the parity buffer must
 115                         be initialized before calling the encoder.
 116                 </para>
 117                 <para>
 118                         The expanded data can be inverted on the fly by
 119                         providing a non zero inversion mask. The expanded data is
 120                         XOR'ed with the mask. This is used e.g. for FLASH
 121                         ECC, where the all 0xFF is inverted to an all 0x00.
 122                         The Reed-Solomon code for all 0x00 is all 0x00. The
 123                         code is inverted before storing to FLASH so it is 0xFF
 124                         too. This prevent's that reading from an erased FLASH
 125                         results in ECC errors.
 126                 </para>
 127                 <para>
 128                         The databytes are expanded to the given symbol size
 129                         on the fly. There is no support for encoding continuous
 130                         bitstreams with a symbol size != 8 at the moment. If
 131                         it is necessary it should be not a big deal to implement
 132                         such functionality.
 133                 </para>
 134                 <programlisting>
 135 /* Parity buffer. Size = number of roots */
 136 uint16_t par[6];
 137 /* Initialize the parity buffer */
 138 memset(par, 0, sizeof(par));
 139 /* Encode 512 byte in data8. Store parity in buffer par */
 140 encode_rs8 (rs_decoder, data8, 512, par, 0);
 141                 </programlisting>
 142         </sect1>
 143         <sect1>
 144                 <title>Decoding</title>
 145                 <para>
 146                         The decoder calculates the syndrome over
 147                         the given data length and the received parity symbols
 148                         and corrects errors in the data.
 149                 </para>
 150                 <para>
 151                         If a syndrome is available from a hardware decoder
 152                         then the syndrome calculation is skipped.
 153                 </para>
 154                 <para>
 155                         The correction of the data buffer can be suppressed
 156                         by providing a correction pattern buffer and an error
 157                         location buffer to the decoder. The decoder stores the
 158                         calculated error location and the correction bitmask
 159                         in the given buffers. This is useful for hardware
 160                         decoders which use a weird bit ordering scheme.
 161                 </para>
 162                 <para>
 163                         The databytes are expanded to the given symbol size
 164                         on the fly. There is no support for decoding continuous
 165                         bitstreams with a symbolsize != 8 at the moment. If
 166                         it is necessary it should be not a big deal to implement
 167                         such functionality.
 168                 </para>
 169
 170                 <sect2>
 171                 <title>
 172                         Decoding with syndrome calculation, direct data correction
 173                 </title>
 174                 <programlisting>
 175 /* Parity buffer. Size = number of roots */
 176 uint16_t par[6];
 177 uint8_t  data[512];
 178 int numerr;
 179 /* Receive data */
 180 .....
 181 /* Receive parity */
 182 .....
 183 /* Decode 512 byte in data8.*/
 184 numerr = decode_rs8 (rs_decoder, data8, par, 512, NULL, 0, NULL, 0, NULL);
 185                 </programlisting>
 186                 </sect2>
 187
 188                 <sect2>
 189                 <title>
 190                         Decoding with syndrome given by hardware decoder, direct data correction
 191                 </title>
 192                 <programlisting>
 193 /* Parity buffer. Size = number of roots */
 194 uint16_t par[6], syn[6];
 195 uint8_t  data[512];
 196 int numerr;
 197 /* Receive data */
 198 .....
 199 /* Receive parity */
 200 .....
 201 /* Get syndrome from hardware decoder */
 202 .....
 203 /* Decode 512 byte in data8.*/
 204 numerr = decode_rs8 (rs_decoder, data8, par, 512, syn, 0, NULL, 0, NULL);
 205                 </programlisting>
 206                 </sect2>
 207
 208                 <sect2>
 209                 <title>
 210                         Decoding with syndrome given by hardware decoder, no direct data correction.
 211                 </title>
 212                 <para>
 213                         Note: It's not necessary to give data and received parity to the decoder.
 214                 </para>
 215                 <programlisting>
 216 /* Parity buffer. Size = number of roots */
 217 uint16_t par[6], syn[6], corr[8];
 218 uint8_t  data[512];
 219 int numerr, errpos[8];
 220 /* Receive data */
 221 .....
 222 /* Receive parity */
 223 .....
 224 /* Get syndrome from hardware decoder */
 225 .....
 226 /* Decode 512 byte in data8.*/
 227 numerr = decode_rs8 (rs_decoder, NULL, NULL, 512, syn, 0, errpos, 0, corr);
 228 for (i = 0; i &lt; numerr; i++) {
 229         do_error_correction_in_your_buffer(errpos[i], corr[i]);
 230 }
 231                 </programlisting>
 232                 </sect2>
 233         </sect1>
 234         <sect1>
 235                 <title>Cleanup</title>
 236                 <para>
 237                         The function free_rs frees the allocated resources,
 238                         if the caller is the last user of the decoder.
 239                 </para>
 240                 <programlisting>
 241 /* Release resources */
 242 free_rs(rs_decoder);
 243                 </programlisting>
 244         </sect1>
 245
 246   </chapter>
 247
 248   <chapter id="structs">
 249      <title>Structures</title>
 250      <para>
 251      This chapter contains the autogenerated documentation of the structures which are
 252      used in the Reed-Solomon Library and are relevant for a developer.
 253      </para>
 254 !Iinclude/linux/rslib.h
 255   </chapter>
 256
 257   <chapter id="pubfunctions">
 258      <title>Public Functions Provided</title>
 259      <para>
 260      This chapter contains the autogenerated documentation of the Reed-Solomon functions
 261      which are exported.
 262      </para>
 263 !Elib/reed_solomon/reed_solomon.c
 264   </chapter>
 265
 266   <chapter id="credits">
 267      <title>Credits</title>
 268         <para>
 269                 The library code for encoding and decoding was written by Phil Karn.
 270         </para>
 271         <programlisting>
 272                 Copyright 2002, Phil Karn, KA9Q
 273                 May be used under the terms of the GNU General Public License (GPL)
 274         </programlisting>
 275         <para>
 276                 The wrapper functions and interfaces are written by Thomas Gleixner
 277         </para>
 278         <para>
 279                 Many users have provided bugfixes, improvements and helping hands for testing.
 280                 Thanks a lot.
 281         </para>
 282         <para>
 283                 The following people have contributed to this document:
 284         </para>
 285         <para>
 286                 Thomas Gleixner<email>tglx@linutronix.de</email>
 287         </para>
 288   </chapter>
 289 </book>