[mirror_ubuntu-zesty-kernel.git] / Documentation / DocBook / librs.tmpl

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>

<book id="Reed-Solomon-Library-Guide">
 <bookinfo>
  <title>Reed-Solomon Library Programming Interface</title>
  
  <authorgroup>
   <author>
    <firstname>Thomas</firstname>
    <surname>Gleixner</surname>
    <affiliation>
     <address>
      <email>tglx@linutronix.de</email>
     </address>
    </affiliation>
   </author>
  </authorgroup>

  <copyright>
   <year>2004</year>
   <holder>Thomas Gleixner</holder>
  </copyright>

  <legalnotice>
   <para>
     This documentation is free software; you can redistribute
     it and/or modify it under the terms of the GNU General Public
     License version 2 as published by the Free Software Foundation.
   </para>
      
   <para>
     This program is distributed in the hope that it will be
     useful, but WITHOUT ANY WARRANTY; without even the implied
     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
     See the GNU General Public License for more details.
   </para>
      
   <para>
     You should have received a copy of the GNU General Public
     License along with this program; if not, write to the Free
     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
     MA 02111-1307 USA
   </para>
      
   <para>
     For more details see the file COPYING in the source
     distribution of Linux.
   </para>
  </legalnotice>
 </bookinfo>

<toc></toc>

  <chapter id="intro">
      <title>Introduction</title>
  <para>
  	The generic Reed-Solomon Library provides encoding, decoding
	and error correction functions.
  </para>
  <para>
  	Reed-Solomon codes are used in communication and storage
	applications to ensure data integrity. 
  </para>
  <para>
  	This documentation is provided for developers who want to utilize
	the functions provided by the library.
  </para>
  </chapter>
  
  <chapter id="bugs">
     <title>Known Bugs And Assumptions</title>
  <para>
	None.	
  </para>
  </chapter>

  <chapter id="usage">
     	<title>Usage</title>
	<para>
		This chapter provides examples of how to use the library.
	</para>
	<sect1>
		<title>Initializing</title>
		<para>
			The init function init_rs returns a pointer to an
			rs decoder structure, which holds the necessary
			information for encoding, decoding and error correction
			with the given polynomial. It either uses an existing
			matching decoder or creates a new one. On creation all
			the lookup tables for fast en/decoding are created.
			The function may take a while, so make sure not to 
			call it in critical code paths.
		</para>
		<programlisting>
/* the Reed Solomon control structure */
static struct rs_control *rs_decoder;

/* Symbolsize is 10 (bits)
 * Primitive polynomial is x^10+x^3+1
 * first consecutive root is 0
 * primitive element to generate roots = 1
 * generator polynomial degree (number of roots) = 6
 */
rs_decoder = init_rs (10, 0x409, 0, 1, 6);
		</programlisting>
	</sect1>
	<sect1>
		<title>Encoding</title>
		<para>
			The encoder calculates the Reed-Solomon code over
			the given data length and stores the result in 
			the parity buffer. Note that the parity buffer must
			be initialized before calling the encoder.
		</para>
		<para>
			The expanded data can be inverted on the fly by
			providing a non-zero inversion mask. The expanded data is
			XOR'ed with the mask. This is used e.g. for FLASH
			ECC, where the all 0xFF is inverted to an all 0x00.
			The Reed-Solomon code for all 0x00 is all 0x00. The
			code is inverted before storing to FLASH so it is 0xFF
			too. This prevents that reading from an erased FLASH
			results in ECC errors.
		</para>
		<para>
			The databytes are expanded to the given symbol size
			on the fly. There is no support for encoding continuous
			bitstreams with a symbol size != 8 at the moment. If
			it is necessary it should be not a big deal to implement
			such functionality.
		</para>
		<programlisting>
/* Parity buffer. Size = number of roots */
uint16_t par[6];
/* Initialize the parity buffer */
memset(par, 0, sizeof(par));
/* Encode 512 byte in data8. Store parity in buffer par */
encode_rs8 (rs_decoder, data8, 512, par, 0);
		</programlisting>
	</sect1>
	<sect1>
		<title>Decoding</title>
		<para>
			The decoder calculates the syndrome over
			the given data length and the received parity symbols
			and corrects errors in the data.
		</para>
		<para>
			If a syndrome is available from a hardware decoder
			then the syndrome calculation is skipped.
		</para>
		<para>
			The correction of the data buffer can be suppressed
			by providing a correction pattern buffer and an error
			location buffer to the decoder. The decoder stores the
			calculated error location and the correction bitmask
			in the given buffers. This is useful for hardware
			decoders which use a weird bit ordering scheme.
		</para>
		<para>
			The databytes are expanded to the given symbol size
			on the fly. There is no support for decoding continuous
			bitstreams with a symbolsize != 8 at the moment. If
			it is necessary it should be not a big deal to implement
			such functionality.
		</para>
		
		<sect2>
		<title>
			Decoding with syndrome calculation, direct data correction
		</title>
		<programlisting>
/* Parity buffer. Size = number of roots */
uint16_t par[6];
uint8_t  data[512];
int numerr;
/* Receive data */
.....
/* Receive parity */
.....
/* Decode 512 byte in data8.*/
numerr = decode_rs8 (rs_decoder, data8, par, 512, NULL, 0, NULL, 0, NULL);
		</programlisting>
		</sect2>

		<sect2>
		<title>
			Decoding with syndrome given by hardware decoder, direct data correction
		</title>
		<programlisting>
/* Parity buffer. Size = number of roots */
uint16_t par[6], syn[6];
uint8_t  data[512];
int numerr;
/* Receive data */
.....
/* Receive parity */
.....
/* Get syndrome from hardware decoder */
.....
/* Decode 512 byte in data8.*/
numerr = decode_rs8 (rs_decoder, data8, par, 512, syn, 0, NULL, 0, NULL);
		</programlisting>
		</sect2>

		<sect2>
		<title>
			Decoding with syndrome given by hardware decoder, no direct data correction.
		</title>
		<para>
			Note: It's not necessary to give data and received parity to the decoder.
		</para>
		<programlisting>
/* Parity buffer. Size = number of roots */
uint16_t par[6], syn[6], corr[8];
uint8_t  data[512];
int numerr, errpos[8];
/* Receive data */
.....
/* Receive parity */
.....
/* Get syndrome from hardware decoder */
.....
/* Decode 512 byte in data8.*/
numerr = decode_rs8 (rs_decoder, NULL, NULL, 512, syn, 0, errpos, 0, corr);
for (i = 0; i &lt; numerr; i++) {
	do_error_correction_in_your_buffer(errpos[i], corr[i]);
}
		</programlisting>
		</sect2>
	</sect1>
	<sect1>
		<title>Cleanup</title>
		<para>
			The function free_rs frees the allocated resources,
			if the caller is the last user of the decoder.
		</para>
		<programlisting>
/* Release resources */
free_rs(rs_decoder);
		</programlisting>
	</sect1>

  </chapter>
	
  <chapter id="structs">
     <title>Structures</title>
     <para>
     This chapter contains the autogenerated documentation of the structures which are
     used in the Reed-Solomon Library and are relevant for a developer.
     </para>
!Iinclude/linux/rslib.h
  </chapter>

  <chapter id="pubfunctions">
     <title>Public Functions Provided</title>
     <para>
     This chapter contains the autogenerated documentation of the Reed-Solomon functions
     which are exported.
     </para>
!Elib/reed_solomon/reed_solomon.c
  </chapter>
  
  <chapter id="credits">
     <title>Credits</title>
	<para>
		The library code for encoding and decoding was written by Phil Karn.
	</para>
	<programlisting>
		Copyright 2002, Phil Karn, KA9Q
 		May be used under the terms of the GNU General Public License (GPL)
	</programlisting>
	<para>
		The wrapper functions and interfaces are written by Thomas Gleixner.
	</para>
	<para>
		Many users have provided bugfixes, improvements and helping hands for testing.
		Thanks a lot.
	</para>
	<para>
		The following people have contributed to this document:
	</para>
	<para>
		Thomas Gleixner<email>tglx@linutronix.de</email>
	</para>
  </chapter>
</book>
Commit	Line	Data
1da177e4 LT	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>
58235413	82	This chapter provides examples of how to use the library.
1da177e4 LT	83	</para>
	84	<sect1>
	85	<title>Initializing</title>
	86	<para>
58235413	87	The init function init_rs returns a pointer to an
1da177e4 LT	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)
58235413	101	* Primitive polynomial is x^10+x^3+1
1da177e4	102	* first consecutive root is 0
58235413 RD	103	* primitive element to generate roots = 1
58235413 RD	104	* generator polynomial degree (number of roots) = 6
1da177e4 LT	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
58235413	119	providing a non-zero inversion mask. The expanded data is
1da177e4 LT	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
58235413	124	too. This prevents that reading from an erased FLASH
1da177e4 LT	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 < 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>
58235413	276	The wrapper functions and interfaces are written by Thomas Gleixner.
1da177e4 LT	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>