--- /dev/null
+/*
+ * YAFFS: Yet Another Flash File System. A NAND-flash specific file system.
+ *
+ * Copyright (C) 2002-2011 Aleph One Ltd.
+ * for Toby Churchill Ltd and Brightstar Engineering
+ *
+ * Created by Charles Manning <charles@aleph1.co.uk>
+ *
+ * This program 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.
+ */
+
+/*
+ * This code implements the ECC algorithm used in SmartMedia.
+ *
+ * The ECC comprises 22 bits of parity information and is stuffed into 3 bytes.
+ * The two unused bit are set to 1.
+ * The ECC can correct single bit errors in a 256-byte page of data. Thus, two
+ * such ECC blocks are used on a 512-byte NAND page.
+ *
+ */
+
+#include "yportenv.h"
+
+#include "yaffs_ecc.h"
+
+/* Table generated by gen-ecc.c
+ * Using a table means we do not have to calculate p1..p4 and p1'..p4'
+ * for each byte of data. These are instead provided in a table in bits7..2.
+ * Bit 0 of each entry indicates whether the entry has an odd or even parity,
+ * and therefore this bytes influence on the line parity.
+ */
+
+static const unsigned char column_parity_table[] = {
+ 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
+ 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
+ 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
+ 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
+ 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
+ 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
+ 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
+ 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
+ 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
+ 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
+ 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
+ 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
+ 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
+ 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
+ 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
+ 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
+ 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
+ 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
+ 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
+ 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
+ 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
+ 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
+ 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
+ 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
+ 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
+ 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
+ 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
+ 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
+ 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
+ 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
+ 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
+ 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
+};
+
+
+/* Calculate the ECC for a 256-byte block of data */
+void yaffs_ecc_calc(const unsigned char *data, unsigned char *ecc)
+{
+ unsigned int i;
+ unsigned char col_parity = 0;
+ unsigned char line_parity = 0;
+ unsigned char line_parity_prime = 0;
+ unsigned char t;
+ unsigned char b;
+
+ for (i = 0; i < 256; i++) {
+ b = column_parity_table[*data++];
+ col_parity ^= b;
+
+ if (b & 0x01) { /* odd number of bits in the byte */
+ line_parity ^= i;
+ line_parity_prime ^= ~i;
+ }
+ }
+
+ ecc[2] = (~col_parity) | 0x03;
+
+ t = 0;
+ if (line_parity & 0x80)
+ t |= 0x80;
+ if (line_parity_prime & 0x80)
+ t |= 0x40;
+ if (line_parity & 0x40)
+ t |= 0x20;
+ if (line_parity_prime & 0x40)
+ t |= 0x10;
+ if (line_parity & 0x20)
+ t |= 0x08;
+ if (line_parity_prime & 0x20)
+ t |= 0x04;
+ if (line_parity & 0x10)
+ t |= 0x02;
+ if (line_parity_prime & 0x10)
+ t |= 0x01;
+ ecc[1] = ~t;
+
+ t = 0;
+ if (line_parity & 0x08)
+ t |= 0x80;
+ if (line_parity_prime & 0x08)
+ t |= 0x40;
+ if (line_parity & 0x04)
+ t |= 0x20;
+ if (line_parity_prime & 0x04)
+ t |= 0x10;
+ if (line_parity & 0x02)
+ t |= 0x08;
+ if (line_parity_prime & 0x02)
+ t |= 0x04;
+ if (line_parity & 0x01)
+ t |= 0x02;
+ if (line_parity_prime & 0x01)
+ t |= 0x01;
+ ecc[0] = ~t;
+
+}
+
+/* Correct the ECC on a 256 byte block of data */
+
+int yaffs_ecc_correct(unsigned char *data, unsigned char *read_ecc,
+ const unsigned char *test_ecc)
+{
+ unsigned char d0, d1, d2; /* deltas */
+
+ d0 = read_ecc[0] ^ test_ecc[0];
+ d1 = read_ecc[1] ^ test_ecc[1];
+ d2 = read_ecc[2] ^ test_ecc[2];
+
+ if ((d0 | d1 | d2) == 0)
+ return 0; /* no error */
+
+ if (((d0 ^ (d0 >> 1)) & 0x55) == 0x55 &&
+ ((d1 ^ (d1 >> 1)) & 0x55) == 0x55 &&
+ ((d2 ^ (d2 >> 1)) & 0x54) == 0x54) {
+ /* Single bit (recoverable) error in data */
+
+ unsigned byte;
+ unsigned bit;
+
+ bit = byte = 0;
+
+ if (d1 & 0x80)
+ byte |= 0x80;
+ if (d1 & 0x20)
+ byte |= 0x40;
+ if (d1 & 0x08)
+ byte |= 0x20;
+ if (d1 & 0x02)
+ byte |= 0x10;
+ if (d0 & 0x80)
+ byte |= 0x08;
+ if (d0 & 0x20)
+ byte |= 0x04;
+ if (d0 & 0x08)
+ byte |= 0x02;
+ if (d0 & 0x02)
+ byte |= 0x01;
+
+ if (d2 & 0x80)
+ bit |= 0x04;
+ if (d2 & 0x20)
+ bit |= 0x02;
+ if (d2 & 0x08)
+ bit |= 0x01;
+
+ data[byte] ^= (1 << bit);
+
+ return 1; /* Corrected the error */
+ }
+
+ if ((hweight8(d0) + hweight8(d1) + hweight8(d2)) == 1) {
+ /* Reccoverable error in ecc */
+
+ read_ecc[0] = test_ecc[0];
+ read_ecc[1] = test_ecc[1];
+ read_ecc[2] = test_ecc[2];
+
+ return 1; /* Corrected the error */
+ }
+
+ /* Unrecoverable error */
+
+ return -1;
+
+}
+
+/*
+ * ECCxxxOther does ECC calcs on arbitrary n bytes of data
+ */
+void yaffs_ecc_calc_other(const unsigned char *data, unsigned n_bytes,
+ struct yaffs_ecc_other *ecc_other)
+{
+ unsigned int i;
+ unsigned char col_parity = 0;
+ unsigned line_parity = 0;
+ unsigned line_parity_prime = 0;
+ unsigned char b;
+
+ for (i = 0; i < n_bytes; i++) {
+ b = column_parity_table[*data++];
+ col_parity ^= b;
+
+ if (b & 0x01) {
+ /* odd number of bits in the byte */
+ line_parity ^= i;
+ line_parity_prime ^= ~i;
+ }
+
+ }
+
+ ecc_other->col_parity = (col_parity >> 2) & 0x3f;
+ ecc_other->line_parity = line_parity;
+ ecc_other->line_parity_prime = line_parity_prime;
+}
+
+int yaffs_ecc_correct_other(unsigned char *data, unsigned n_bytes,
+ struct yaffs_ecc_other *read_ecc,
+ const struct yaffs_ecc_other *test_ecc)
+{
+ unsigned char delta_col; /* column parity delta */
+ unsigned delta_line; /* line parity delta */
+ unsigned delta_line_prime; /* line parity delta */
+ unsigned bit;
+
+ delta_col = read_ecc->col_parity ^ test_ecc->col_parity;
+ delta_line = read_ecc->line_parity ^ test_ecc->line_parity;
+ delta_line_prime =
+ read_ecc->line_parity_prime ^ test_ecc->line_parity_prime;
+
+ if ((delta_col | delta_line | delta_line_prime) == 0)
+ return 0; /* no error */
+
+ if (delta_line == ~delta_line_prime &&
+ (((delta_col ^ (delta_col >> 1)) & 0x15) == 0x15)) {
+ /* Single bit (recoverable) error in data */
+
+ bit = 0;
+
+ if (delta_col & 0x20)
+ bit |= 0x04;
+ if (delta_col & 0x08)
+ bit |= 0x02;
+ if (delta_col & 0x02)
+ bit |= 0x01;
+
+ if (delta_line >= n_bytes)
+ return -1;
+
+ data[delta_line] ^= (1 << bit);
+
+ return 1; /* corrected */
+ }
+
+ if ((hweight32(delta_line) +
+ hweight32(delta_line_prime) +
+ hweight8(delta_col)) == 1) {
+ /* Reccoverable error in ecc */
+
+ *read_ecc = *test_ecc;
+ return 1; /* corrected */
+ }
+
+ /* Unrecoverable error */
+
+ return -1;
+}
Code Review / kvmfornfv.git / blobdiff