nand_ecc.c

   1 /*
   2  *  drivers/mtd/nand_ecc.c
   3  *
   4  *  Copyright (C) 2000 Steven J. Hill (sjhill@cotw.com)
   5  *                     Toshiba America Electronics Components, Inc.
   6  *
   7  * $Id: nand_ecc.c,v 1.1 2002-05-27 18:57:25 charles Exp $
   8  *
   9  * This program is free software; you can redistribute it and/or modify
  10  * it under the terms of the GNU General Public License version 2 as
  11  * published by the Free Software Foundation.
  12  *
  13  * This file contains an ECC algorithm from Toshiba that detects and
  14  * corrects 1 bit errors in a 256 byte block of data.
  15  *
  16  *
  17  *  Slightly hacked to fit in with YAFFS by Charles Manning.
  18  */
  19 #if 0
  20 #include <linux/types.h>
  21 #include <linux/kernel.h>
  22 #include <linux/module.h>
  23 #endif
  24
  25 #include "yportenv.h"
  26
  27 /*
  28  * Pre-calculated 256-way 1 byte column parity
  29  */
  30 static const u_char nand_ecc_precalc_table[] = {
  31         0x00, 0x55, 0x56, 0x03, 0x59, 0x0c, 0x0f, 0x5a, 0x5a, 0x0f, 0x0c, 0x59, 0x03, 0x56, 0x55, 0x00,
  32         0x65, 0x30, 0x33, 0x66, 0x3c, 0x69, 0x6a, 0x3f, 0x3f, 0x6a, 0x69, 0x3c, 0x66, 0x33, 0x30, 0x65,
  33         0x66, 0x33, 0x30, 0x65, 0x3f, 0x6a, 0x69, 0x3c, 0x3c, 0x69, 0x6a, 0x3f, 0x65, 0x30, 0x33, 0x66,
  34         0x03, 0x56, 0x55, 0x00, 0x5a, 0x0f, 0x0c, 0x59, 0x59, 0x0c, 0x0f, 0x5a, 0x00, 0x55, 0x56, 0x03,
  35         0x69, 0x3c, 0x3f, 0x6a, 0x30, 0x65, 0x66, 0x33, 0x33, 0x66, 0x65, 0x30, 0x6a, 0x3f, 0x3c, 0x69,
  36         0x0c, 0x59, 0x5a, 0x0f, 0x55, 0x00, 0x03, 0x56, 0x56, 0x03, 0x00, 0x55, 0x0f, 0x5a, 0x59, 0x0c,
  37         0x0f, 0x5a, 0x59, 0x0c, 0x56, 0x03, 0x00, 0x55, 0x55, 0x00, 0x03, 0x56, 0x0c, 0x59, 0x5a, 0x0f,
  38         0x6a, 0x3f, 0x3c, 0x69, 0x33, 0x66, 0x65, 0x30, 0x30, 0x65, 0x66, 0x33, 0x69, 0x3c, 0x3f, 0x6a,
  39         0x6a, 0x3f, 0x3c, 0x69, 0x33, 0x66, 0x65, 0x30, 0x30, 0x65, 0x66, 0x33, 0x69, 0x3c, 0x3f, 0x6a,
  40         0x0f, 0x5a, 0x59, 0x0c, 0x56, 0x03, 0x00, 0x55, 0x55, 0x00, 0x03, 0x56, 0x0c, 0x59, 0x5a, 0x0f,
  41         0x0c, 0x59, 0x5a, 0x0f, 0x55, 0x00, 0x03, 0x56, 0x56, 0x03, 0x00, 0x55, 0x0f, 0x5a, 0x59, 0x0c,
  42         0x69, 0x3c, 0x3f, 0x6a, 0x30, 0x65, 0x66, 0x33, 0x33, 0x66, 0x65, 0x30, 0x6a, 0x3f, 0x3c, 0x69,
  43         0x03, 0x56, 0x55, 0x00, 0x5a, 0x0f, 0x0c, 0x59, 0x59, 0x0c, 0x0f, 0x5a, 0x00, 0x55, 0x56, 0x03,
  44         0x66, 0x33, 0x30, 0x65, 0x3f, 0x6a, 0x69, 0x3c, 0x3c, 0x69, 0x6a, 0x3f, 0x65, 0x30, 0x33, 0x66,
  45         0x65, 0x30, 0x33, 0x66, 0x3c, 0x69, 0x6a, 0x3f, 0x3f, 0x6a, 0x69, 0x3c, 0x66, 0x33, 0x30, 0x65,
  46         0x00, 0x55, 0x56, 0x03, 0x59, 0x0c, 0x0f, 0x5a, 0x5a, 0x0f, 0x0c, 0x59, 0x03, 0x56, 0x55, 0x00
  47 };
  48
  49
  50 /*
  51  * Creates non-inverted ECC code from line parity
  52  */
  53 static void nand_trans_result(u_char reg2, u_char reg3,
  54         u_char *ecc_code)
  55 {
  56         u_char a, b, i, tmp1, tmp2;
  57
  58         /* Initialize variables */
  59         a = b = 0x80;
  60         tmp1 = tmp2 = 0;
  61
  62         /* Calculate first ECC byte */
  63         for (i = 0; i < 4; i++) {
  64                 if (reg3 & a)           /* LP15,13,11,9 --> ecc_code[0] */
  65                         tmp1 |= b;
  66                 b >>= 1;
  67                 if (reg2 & a)           /* LP14,12,10,8 --> ecc_code[0] */
  68                         tmp1 |= b;
  69                 b >>= 1;
  70                 a >>= 1;
  71         }
  72
  73         /* Calculate second ECC byte */
  74         b = 0x80;
  75         for (i = 0; i < 4; i++) {
  76                 if (reg3 & a)           /* LP7,5,3,1 --> ecc_code[1] */
  77                         tmp2 |= b;
  78                 b >>= 1;
  79                 if (reg2 & a)           /* LP6,4,2,0 --> ecc_code[1] */
  80                         tmp2 |= b;
  81                 b >>= 1;
  82                 a >>= 1;
  83         }
  84
  85         /* Store two of the ECC bytes */
  86         ecc_code[0] = tmp1;
  87         ecc_code[1] = tmp2;
  88 }
  89
  90 /*
  91  * Calculate 3 byte ECC code for 256 byte block
  92  */
  93 void nand_calculate_ecc (const u_char *dat, u_char *ecc_code)
  94 {
  95         u_char idx, reg1, reg2, reg3;
  96         int j;
  97
  98         /* Initialize variables */
  99         reg1 = reg2 = reg3 = 0;
 100         ecc_code[0] = ecc_code[1] = ecc_code[2] = 0;
 101
 102         /* Build up column parity */
 103         for(j = 0; j < 256; j++) {
 104
 105                 /* Get CP0 - CP5 from table */
 106                 idx = nand_ecc_precalc_table[dat[j]];
 107                 reg1 ^= (idx & 0x3f);
 108
 109                 /* All bit XOR = 1 ? */
 110                 if (idx & 0x40) {
 111                         reg3 ^= (u_char) j;
 112                         reg2 ^= ~((u_char) j);
 113                 }
 114         }
 115
 116         /* Create non-inverted ECC code from line parity */
 117         nand_trans_result(reg2, reg3, ecc_code);
 118
 119         /* Calculate final ECC code */
 120         ecc_code[0] = ~ecc_code[0];
 121         ecc_code[1] = ~ecc_code[1];
 122         ecc_code[2] = ((~reg1) << 2) | 0x03;
 123 }
 124
 125 /*
 126  * Detect and correct a 1 bit error for 256 byte block
 127  */
 128 int nand_correct_data (u_char *dat, u_char *read_ecc, u_char *calc_ecc)
 129 {
 130         u_char a, b, c, d1, d2, d3, add, bit, i;
 131
 132         /* Do error detection */
 133         d1 = calc_ecc[0] ^ read_ecc[0];
 134         d2 = calc_ecc[1] ^ read_ecc[1];
 135         d3 = calc_ecc[2] ^ read_ecc[2];
 136
 137         if ((d1 | d2 | d3) == 0) {
 138                 /* No errors */
 139                 return 0;
 140         }
 141         else {
 142                 a = (d1 ^ (d1 >> 1)) & 0x55;
 143                 b = (d2 ^ (d2 >> 1)) & 0x55;
 144                 c = (d3 ^ (d3 >> 1)) & 0x54;
 145
 146                 /* Found and will correct single bit error in the data */
 147                 if ((a == 0x55) && (b == 0x55) && (c == 0x54)) {
 148                         c = 0x80;
 149                         add = 0;
 150                         a = 0x80;
 151                         for (i=0; i<4; i++) {
 152                                 if (d1 & c)
 153                                         add |= a;
 154                                 c >>= 2;
 155                                 a >>= 1;
 156                         }
 157                         c = 0x80;
 158                         for (i=0; i<4; i++) {
 159                                 if (d2 & c)
 160                                         add |= a;
 161                                 c >>= 2;
 162                                 a >>= 1;
 163                         }
 164                         bit = 0;
 165                         b = 0x04;
 166                         c = 0x80;
 167                         for (i=0; i<3; i++) {
 168                                 if (d3 & c)
 169                                         bit |= b;
 170                                 c >>= 2;
 171                                 b >>= 1;
 172                         }
 173                         b = 0x01;
 174                         a = dat[add];
 175                         a ^= (b << bit);
 176                         dat[add] = a;
 177                         return 1;
 178                 }
 179                 else {
 180                         i = 0;
 181                         while (d1) {
 182                                 if (d1 & 0x01)
 183                                         ++i;
 184                                 d1 >>= 1;
 185                         }
 186                         while (d2) {
 187                                 if (d2 & 0x01)
 188                                         ++i;
 189                                 d2 >>= 1;
 190                         }
 191                         while (d3) {
 192                                 if (d3 & 0x01)
 193                                         ++i;
 194                                 d3 >>= 1;
 195                         }
 196                         if (i == 1) {
 197                                 /* ECC Code Error Correction */
 198                                 read_ecc[0] = calc_ecc[0];
 199                                 read_ecc[1] = calc_ecc[1];
 200                                 read_ecc[2] = calc_ecc[2];
 201                                 return 2;
 202                         }
 203                         else {
 204                                 /* Uncorrectable Error */
 205                                 return -1;
 206                         }
 207                 }
 208         }
 209
 210         /* Should never happen */
 211         return -1;
 212 }
 213
 214
 215 #if 0
 216 EXPORT_SYMBOL(nand_calculate_ecc);
 217 EXPORT_SYMBOL(nand_correct_data);
 218 #endif
 219