ecc.h

   1 /*
   2  * Calculate Error-correcting Codes. Used by NAND Flash controllers
   3  * (not by NAND chips).
   4  *
   5  * Copyright (c) 2006 Openedhand Ltd.
   6  * Written by Andrzej Zaborowski <balrog@zabor.org>
   7  *
   8  * This code is licensed under the GNU GPL v2.
   9  */
  10
  11 struct ecc_state_s {
  12     uint8_t cp;         /* Column parity */
  13     uint16_t lp[2];     /* Line parity */
  14     uint16_t count;
  15 };
  16
  17 /*
  18  * Pre-calculated 256-way 1 byte column parity.  Table borrowed from Linux.
  19  */
  20 static const uint8_t nand_ecc_precalc_table[] = {
  21     0x00, 0x55, 0x56, 0x03, 0x59, 0x0c, 0x0f, 0x5a,
  22     0x5a, 0x0f, 0x0c, 0x59, 0x03, 0x56, 0x55, 0x00,
  23     0x65, 0x30, 0x33, 0x66, 0x3c, 0x69, 0x6a, 0x3f,
  24     0x3f, 0x6a, 0x69, 0x3c, 0x66, 0x33, 0x30, 0x65,
  25     0x66, 0x33, 0x30, 0x65, 0x3f, 0x6a, 0x69, 0x3c,
  26     0x3c, 0x69, 0x6a, 0x3f, 0x65, 0x30, 0x33, 0x66,
  27     0x03, 0x56, 0x55, 0x00, 0x5a, 0x0f, 0x0c, 0x59,
  28     0x59, 0x0c, 0x0f, 0x5a, 0x00, 0x55, 0x56, 0x03,
  29     0x69, 0x3c, 0x3f, 0x6a, 0x30, 0x65, 0x66, 0x33,
  30     0x33, 0x66, 0x65, 0x30, 0x6a, 0x3f, 0x3c, 0x69,
  31     0x0c, 0x59, 0x5a, 0x0f, 0x55, 0x00, 0x03, 0x56,
  32     0x56, 0x03, 0x00, 0x55, 0x0f, 0x5a, 0x59, 0x0c,
  33     0x0f, 0x5a, 0x59, 0x0c, 0x56, 0x03, 0x00, 0x55,
  34     0x55, 0x00, 0x03, 0x56, 0x0c, 0x59, 0x5a, 0x0f,
  35     0x6a, 0x3f, 0x3c, 0x69, 0x33, 0x66, 0x65, 0x30,
  36     0x30, 0x65, 0x66, 0x33, 0x69, 0x3c, 0x3f, 0x6a,
  37     0x6a, 0x3f, 0x3c, 0x69, 0x33, 0x66, 0x65, 0x30,
  38     0x30, 0x65, 0x66, 0x33, 0x69, 0x3c, 0x3f, 0x6a,
  39     0x0f, 0x5a, 0x59, 0x0c, 0x56, 0x03, 0x00, 0x55,
  40     0x55, 0x00, 0x03, 0x56, 0x0c, 0x59, 0x5a, 0x0f,
  41     0x0c, 0x59, 0x5a, 0x0f, 0x55, 0x00, 0x03, 0x56,
  42     0x56, 0x03, 0x00, 0x55, 0x0f, 0x5a, 0x59, 0x0c,
  43     0x69, 0x3c, 0x3f, 0x6a, 0x30, 0x65, 0x66, 0x33,
  44     0x33, 0x66, 0x65, 0x30, 0x6a, 0x3f, 0x3c, 0x69,
  45     0x03, 0x56, 0x55, 0x00, 0x5a, 0x0f, 0x0c, 0x59,
  46     0x59, 0x0c, 0x0f, 0x5a, 0x00, 0x55, 0x56, 0x03,
  47     0x66, 0x33, 0x30, 0x65, 0x3f, 0x6a, 0x69, 0x3c,
  48     0x3c, 0x69, 0x6a, 0x3f, 0x65, 0x30, 0x33, 0x66,
  49     0x65, 0x30, 0x33, 0x66, 0x3c, 0x69, 0x6a, 0x3f,
  50     0x3f, 0x6a, 0x69, 0x3c, 0x66, 0x33, 0x30, 0x65,
  51     0x00, 0x55, 0x56, 0x03, 0x59, 0x0c, 0x0f, 0x5a,
  52     0x5a, 0x0f, 0x0c, 0x59, 0x03, 0x56, 0x55, 0x00,
  53 };
  54
  55 /* Update ECC parity count.  */
  56 static inline uint8_t ecc_digest(struct ecc_state_s *s, uint8_t sample)
  57 {
  58     uint8_t idx = nand_ecc_precalc_table[sample];
  59
  60     s->cp ^= idx & 0x3f;
  61     if (idx & 0x40) {
  62         s->lp[0] ^= ~s->count;
  63         s->lp[1] ^= s->count;
  64     }
  65     s->count ++;
  66
  67     return sample;
  68 }
  69
  70 /* Reinitialise the counters.  */
  71 static inline void ecc_reset(struct ecc_state_s *s)
  72 {
  73     s->lp[0] = 0x0000;
  74     s->lp[1] = 0x0000;
  75     s->cp = 0x00;
  76     s->count = 0;
  77 }