fs/yaffs2/yaffs_ecc.c

2  * YAFFS: Yet Another Flash File System. A NAND-flash specific file system.
4  * Copyright (C) 2002-2011 Aleph One Ltd.
17  * The ECC comprises 22 bits of parity information and is stuffed into 3 bytes.
19  * The ECC can correct single bit errors in a 256-byte page of data. Thus, two
20  * such ECC blocks are used on a 512-byte NAND page.
28 /* Table generated by gen-ecc.c
31  * Bit 0 of each entry indicates whether the entry has an odd or even parity,
32  * and therefore this bytes influence on the line parity.
71 /* Calculate the ECC for a 256-byte block of data */
85 		if (b & 0x01) {	/* odd number of bits in the byte */  in yaffs_ecc_calc()
198 	return -1;  in yaffs_ecc_correct()
219 			/* odd number of bits in the byte */  in yaffs_ecc_calc_other()
226 	ecc_other->col_parity = (col_parity >> 2) & 0x3f;  in yaffs_ecc_calc_other()
227 	ecc_other->line_parity = line_parity;  in yaffs_ecc_calc_other()
228 	ecc_other->line_parity_prime = line_parity_prime;  in yaffs_ecc_calc_other()
235 	unsigned char delta_col;	/* column parity delta */  in yaffs_ecc_correct_other()
236 	unsigned delta_line;	/* line parity delta */  in yaffs_ecc_correct_other()
237 	unsigned delta_line_prime;	/* line parity delta */  in yaffs_ecc_correct_other()
240 	delta_col = read_ecc->col_parity ^ test_ecc->col_parity;  in yaffs_ecc_correct_other()
241 	delta_line = read_ecc->line_parity ^ test_ecc->line_parity;  in yaffs_ecc_correct_other()
243 	    read_ecc->line_parity_prime ^ test_ecc->line_parity_prime;  in yaffs_ecc_correct_other()
262 			return -1;  in yaffs_ecc_correct_other()
280 	return -1;  in yaffs_ecc_correct_other()