mirror of
https://github.com/torvalds/linux.git
synced 2024-12-04 18:13:04 +00:00
8aba784832
Use pandoc to convert documentation to ReST by calling Documentation/sphinx/tmplcvt script. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
213 lines
5.9 KiB
ReStructuredText
213 lines
5.9 KiB
ReStructuredText
==========================================
|
|
Reed-Solomon Library Programming Interface
|
|
==========================================
|
|
|
|
:Author: Thomas Gleixner
|
|
|
|
Introduction
|
|
============
|
|
|
|
The generic Reed-Solomon Library provides encoding, decoding and error
|
|
correction functions.
|
|
|
|
Reed-Solomon codes are used in communication and storage applications to
|
|
ensure data integrity.
|
|
|
|
This documentation is provided for developers who want to utilize the
|
|
functions provided by the library.
|
|
|
|
Known Bugs And Assumptions
|
|
==========================
|
|
|
|
None.
|
|
|
|
Usage
|
|
=====
|
|
|
|
This chapter provides examples of how to use the library.
|
|
|
|
Initializing
|
|
------------
|
|
|
|
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.
|
|
|
|
::
|
|
|
|
/* 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);
|
|
|
|
|
|
Encoding
|
|
--------
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
::
|
|
|
|
/* 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);
|
|
|
|
|
|
Decoding
|
|
--------
|
|
|
|
The decoder calculates the syndrome over the given data length and the
|
|
received parity symbols and corrects errors in the data.
|
|
|
|
If a syndrome is available from a hardware decoder then the syndrome
|
|
calculation is skipped.
|
|
|
|
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.
|
|
|
|
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.
|
|
|
|
Decoding with syndrome calculation, direct data correction
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
::
|
|
|
|
/* 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);
|
|
|
|
|
|
Decoding with syndrome given by hardware decoder, direct data correction
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
::
|
|
|
|
/* 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);
|
|
|
|
|
|
Decoding with syndrome given by hardware decoder, no direct data correction.
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Note: It's not necessary to give data and received parity to the
|
|
decoder.
|
|
|
|
::
|
|
|
|
/* 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 < numerr; i++) {
|
|
do_error_correction_in_your_buffer(errpos[i], corr[i]);
|
|
}
|
|
|
|
|
|
Cleanup
|
|
-------
|
|
|
|
The function free_rs frees the allocated resources, if the caller is
|
|
the last user of the decoder.
|
|
|
|
::
|
|
|
|
/* Release resources */
|
|
free_rs(rs_decoder);
|
|
|
|
|
|
Structures
|
|
==========
|
|
|
|
This chapter contains the autogenerated documentation of the structures
|
|
which are used in the Reed-Solomon Library and are relevant for a
|
|
developer.
|
|
|
|
.. kernel-doc:: include/linux/rslib.h
|
|
:internal:
|
|
|
|
Public Functions Provided
|
|
=========================
|
|
|
|
This chapter contains the autogenerated documentation of the
|
|
Reed-Solomon functions which are exported.
|
|
|
|
.. kernel-doc:: lib/reed_solomon/reed_solomon.c
|
|
:export:
|
|
|
|
Credits
|
|
=======
|
|
|
|
The library code for encoding and decoding was written by Phil Karn.
|
|
|
|
::
|
|
|
|
Copyright 2002, Phil Karn, KA9Q
|
|
May be used under the terms of the GNU General Public License (GPL)
|
|
|
|
|
|
The wrapper functions and interfaces are written by Thomas Gleixner.
|
|
|
|
Many users have provided bugfixes, improvements and helping hands for
|
|
testing. Thanks a lot.
|
|
|
|
The following people have contributed to this document:
|
|
|
|
Thomas Gleixner\ tglx@linutronix.de
|