os/nandboot-R2_0_4/mtd/nand_ecc.c

Go to the documentation of this file.

/*
 * Taken from  drivers/mtd/nand/nand_ecc.c, from Linux 2.6.16 (IR2_6_16-9)
 * Modified to run outside Linux.
 * #if 0'd to remove non-essential functionality
 *
 * This file contains an ECC algorithm from Toshiba that detects and
 * corrects 1 bit errors in a 256 byte block of data.
 *
 * drivers/mtd/nand/nand_ecc.c
 *
 * Copyright (C) 2000-2004 Steven J. Hill (sjhill@realitydiluted.com)
 *                         Toshiba America Electronics Components, Inc.
 *
 * $Id: nand_ecc.c,v 1.1.1.1 2008/11/27 20:04:00 elphel Exp $
 *
 * This file is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2 or (at your option) any
 * later version.
 *
 * This file 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.
 *
 * You should have received a copy of the GNU General Public License along
 * with this file; if not, write to the Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
 *
 * As a special exception, if other files instantiate templates or use
 * macros or inline functions from these files, or you compile these
 * files and link them with other works to produce a work based on these
 * files, these files do not by themselves cause the resulting work to be
 * covered by the GNU General Public License. However the source code for
 * these files must still be made available in accordance with section (3)
 * of the GNU General Public License.
 *
 * This exception does not invalidate any other reasons why a work based on
 * this file might be covered by the GNU General Public License.
 */

#include <linux/types.h>
#if 0
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/mtd/nand_ecc.h>
#endif

#include "nand_ecc.h"

/*
 * Pre-calculated 256-way 1 byte column parity
 */
static const u_char nand_ecc_precalc_table[] = {
        0x00, 0x55, 0x56, 0x03, 0x59, 0x0c, 0x0f, 0x5a, 0x5a, 0x0f, 0x0c, 0x59, 0x03, 0x56, 0x55, 0x00,
        0x65, 0x30, 0x33, 0x66, 0x3c, 0x69, 0x6a, 0x3f, 0x3f, 0x6a, 0x69, 0x3c, 0x66, 0x33, 0x30, 0x65,
        0x66, 0x33, 0x30, 0x65, 0x3f, 0x6a, 0x69, 0x3c, 0x3c, 0x69, 0x6a, 0x3f, 0x65, 0x30, 0x33, 0x66,
        0x03, 0x56, 0x55, 0x00, 0x5a, 0x0f, 0x0c, 0x59, 0x59, 0x0c, 0x0f, 0x5a, 0x00, 0x55, 0x56, 0x03,
        0x69, 0x3c, 0x3f, 0x6a, 0x30, 0x65, 0x66, 0x33, 0x33, 0x66, 0x65, 0x30, 0x6a, 0x3f, 0x3c, 0x69,
        0x0c, 0x59, 0x5a, 0x0f, 0x55, 0x00, 0x03, 0x56, 0x56, 0x03, 0x00, 0x55, 0x0f, 0x5a, 0x59, 0x0c,
        0x0f, 0x5a, 0x59, 0x0c, 0x56, 0x03, 0x00, 0x55, 0x55, 0x00, 0x03, 0x56, 0x0c, 0x59, 0x5a, 0x0f,
        0x6a, 0x3f, 0x3c, 0x69, 0x33, 0x66, 0x65, 0x30, 0x30, 0x65, 0x66, 0x33, 0x69, 0x3c, 0x3f, 0x6a,
        0x6a, 0x3f, 0x3c, 0x69, 0x33, 0x66, 0x65, 0x30, 0x30, 0x65, 0x66, 0x33, 0x69, 0x3c, 0x3f, 0x6a,
        0x0f, 0x5a, 0x59, 0x0c, 0x56, 0x03, 0x00, 0x55, 0x55, 0x00, 0x03, 0x56, 0x0c, 0x59, 0x5a, 0x0f,
        0x0c, 0x59, 0x5a, 0x0f, 0x55, 0x00, 0x03, 0x56, 0x56, 0x03, 0x00, 0x55, 0x0f, 0x5a, 0x59, 0x0c,
        0x69, 0x3c, 0x3f, 0x6a, 0x30, 0x65, 0x66, 0x33, 0x33, 0x66, 0x65, 0x30, 0x6a, 0x3f, 0x3c, 0x69,
        0x03, 0x56, 0x55, 0x00, 0x5a, 0x0f, 0x0c, 0x59, 0x59, 0x0c, 0x0f, 0x5a, 0x00, 0x55, 0x56, 0x03,
        0x66, 0x33, 0x30, 0x65, 0x3f, 0x6a, 0x69, 0x3c, 0x3c, 0x69, 0x6a, 0x3f, 0x65, 0x30, 0x33, 0x66,
        0x65, 0x30, 0x33, 0x66, 0x3c, 0x69, 0x6a, 0x3f, 0x3f, 0x6a, 0x69, 0x3c, 0x66, 0x33, 0x30, 0x65,
        0x00, 0x55, 0x56, 0x03, 0x59, 0x0c, 0x0f, 0x5a, 0x5a, 0x0f, 0x0c, 0x59, 0x03, 0x56, 0x55, 0x00
};


static void nand_trans_result(u_char reg2, u_char reg3,
        u_char *ecc_code)
{
        u_char a, b, i, tmp1, tmp2;

        /* Initialize variables */
        a = b = 0x80;
        tmp1 = tmp2 = 0;

        /* Calculate first ECC byte */
        for (i = 0; i < 4; i++) {
                if (reg3 & a)           /* LP15,13,11,9 --> ecc_code[0] */
                        tmp1 |= b;
                b >>= 1;
                if (reg2 & a)           /* LP14,12,10,8 --> ecc_code[0] */
                        tmp1 |= b;
                b >>= 1;
                a >>= 1;
        }

        /* Calculate second ECC byte */
        b = 0x80;
        for (i = 0; i < 4; i++) {
                if (reg3 & a)           /* LP7,5,3,1 --> ecc_code[1] */
                        tmp2 |= b;
                b >>= 1;
                if (reg2 & a)           /* LP6,4,2,0 --> ecc_code[1] */
                        tmp2 |= b;
                b >>= 1;
                a >>= 1;
        }

        /* Store two of the ECC bytes */
        ecc_code[0] = tmp1;
        ecc_code[1] = tmp2;
}

int nand_calculate_ecc(struct mtd_info *mtd, const u_char *dat, u_char *ecc_code)
{
        u_char idx, reg1, reg2, reg3;
        int j;

        /* Initialize variables */
        reg1 = reg2 = reg3 = 0;
        ecc_code[0] = ecc_code[1] = ecc_code[2] = 0;

        /* Build up column parity */
        for(j = 0; j < 256; j++) {

                /* Get CP0 - CP5 from table */
                idx = nand_ecc_precalc_table[dat[j]];
                reg1 ^= (idx & 0x3f);

                /* All bit XOR = 1 ? */
                if (idx & 0x40) {
                        reg3 ^= (u_char) j;
                        reg2 ^= ~((u_char) j);
                }
        }

        /* Create non-inverted ECC code from line parity */
        nand_trans_result(reg2, reg3, ecc_code);

        /* Calculate final ECC code */
        ecc_code[0] = ~ecc_code[0];
        ecc_code[1] = ~ecc_code[1];
        ecc_code[2] = ((~reg1) << 2) | 0x03;
        return 0;
}

int nand_correct_data(struct mtd_info *mtd, u_char *dat, u_char *read_ecc, u_char *calc_ecc)
{
        u_char a, b, c, d1, d2, d3, add, bit, i;

        /* Do error detection */
        d1 = calc_ecc[0] ^ read_ecc[0];
        d2 = calc_ecc[1] ^ read_ecc[1];
        d3 = calc_ecc[2] ^ read_ecc[2];

        if ((d1 | d2 | d3) == 0) {
                /* No errors */
                return 0;
        }
        else {
                a = (d1 ^ (d1 >> 1)) & 0x55;
                b = (d2 ^ (d2 >> 1)) & 0x55;
                c = (d3 ^ (d3 >> 1)) & 0x54;

                /* Found and will correct single bit error in the data */
                if ((a == 0x55) && (b == 0x55) && (c == 0x54)) {
                        c = 0x80;
                        add = 0;
                        a = 0x80;
                        for (i=0; i<4; i++) {
                                if (d1 & c)
                                        add |= a;
                                c >>= 2;
                                a >>= 1;
                        }
                        c = 0x80;
                        for (i=0; i<4; i++) {
                                if (d2 & c)
                                        add |= a;
                                c >>= 2;
                                a >>= 1;
                        }
                        bit = 0;
                        b = 0x04;
                        c = 0x80;
                        for (i=0; i<3; i++) {
                                if (d3 & c)
                                        bit |= b;
                                c >>= 2;
                                b >>= 1;
                        }
                        b = 0x01;
                        a = dat[add];
                        a ^= (b << bit);
                        dat[add] = a;
                        return 1;
                }
                else {
                        i = 0;
                        while (d1) {
                                if (d1 & 0x01)
                                        ++i;
                                d1 >>= 1;
                        }
                        while (d2) {
                                if (d2 & 0x01)
                                        ++i;
                                d2 >>= 1;
                        }
                        while (d3) {
                                if (d3 & 0x01)
                                        ++i;
                                d3 >>= 1;
                        }
                        if (i == 1) {
                                /* ECC Code Error Correction */
                                read_ecc[0] = calc_ecc[0];
                                read_ecc[1] = calc_ecc[1];
                                read_ecc[2] = calc_ecc[2];
                                return 2;
                        }
                        else {
                                /* Uncorrectable Error */
                                return -1;
                        }
                }
        }

        /* Should never happen */
        return -1;
}

EXPORT_SYMBOL(nand_calculate_ecc);
EXPORT_SYMBOL(nand_correct_data);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Steven J. Hill <sjhill@realitydiluted.com>");
MODULE_DESCRIPTION("Generic NAND ECC support");

---