4-bit ECC support for Marvell Kirkwood SOC

git-svn-id: svn://svn.berlios.de/openocd/trunk@1768 b42882b7-edfa-0310-969c-e2dbd0fdcd60

1 files changed, 174 insertions, 0 deletions

diff --git a/src/flash/nand_ecc_kw.c b/src/flash/nand_ecc_kw.c
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+++ b/src/flash/nand_ecc_kw.c
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+/*

+ * Reed-Solomon ECC handling for the Marvell Kirkwood SOC

+ * Copyright (C) 2009 Marvell Semiconductor, Inc.

+ *

+ * Authors: Lennert Buytenhek <buytenh@wantstofly.org>

+ *          Nicolas Pitre <nico@cam.org>

+ *

+ * 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.

+ */

+

+#ifdef HAVE_CONFIG_H

+#include "config.h"

+#endif

+

+#include <sys/types.h>

+#include "nand.h"

+

+

+/*****************************************************************************

+ * Arithmetic in GF(2^10) ("F") modulo x^10 + x^3 + 1.

+ *

+ * For multiplication, a discrete log/exponent table is used, with

+ * primitive element x (F is a primitive field, so x is primitive).

+ */

+#define MODPOLY		0x409		/* x^10 + x^3 + 1 in binary */

+

+/*

+ * Maps an integer a [0..1022] to a polynomial b = gf_exp[a] in

+ * GF(2^10) mod x^10 + x^3 + 1 such that b = x ^ a.  There's two

+ * identical copies of this array back-to-back so that we can save

+ * the mod 1023 operation when doing a GF multiplication.

+ */

+static uint16_t gf_exp[1023 + 1023];

+

+/*

+ * Maps a polynomial b in GF(2^10) mod x^10 + x^3 + 1 to an index

+ * a = gf_log[b] in [0..1022] such that b = x ^ a.

+ */

+static uint16_t gf_log[1024];

+

+static void gf_build_log_exp_table(void)

+{

+	int i;

+	int p_i;

+

+	/*

+	 * p_i = x ^ i

+	 *

+	 * Initialise to 1 for i = 0.

+	 */

+	p_i = 1;

+

+	for (i = 0; i < 1023; i++) {

+		gf_exp[i] = p_i;

+		gf_exp[i + 1023] = p_i;

+		gf_log[p_i] = i;

+

+		/*

+		 * p_i = p_i * x

+		 */

+		p_i <<= 1;

+		if (p_i & (1 << 10))

+			p_i ^= MODPOLY;

+	}

+}

+

+

+/*****************************************************************************

+ * Reed-Solomon code

+ *

+ * This implements a (1023,1015) Reed-Solomon ECC code over GF(2^10)

+ * mod x^10 + x^3 + 1, shortened to (520,512).  The ECC data consists

+ * of 8 10-bit symbols, or 10 8-bit bytes.

+ *

+ * Given 512 bytes of data, computes 10 bytes of ECC.

+ *

+ * This is done by converting the 512 bytes to 512 10-bit symbols

+ * (elements of F), interpreting those symbols as a polynomial in F[X]

+ * by taking symbol 0 as the coefficient of X^8 and symbol 511 as the

+ * coefficient of X^519, and calculating the residue of that polynomial

+ * divided by the generator polynomial, which gives us the 8 ECC symbols

+ * as the remainder.  Finally, we convert the 8 10-bit ECC symbols to 10

+ * 8-bit bytes.

+ *

+ * The generator polynomial is hardcoded, as that is faster, but it

+ * can be computed by taking the primitive element a = x (in F), and

+ * constructing a polynomial in F[X] with roots a, a^2, a^3, ..., a^8

+ * by multiplying the minimal polynomials for those roots (which are

+ * just 'x - a^i' for each i).

+ *

+ * Note: due to unfortunate circumstances, the bootrom in the Kirkwood SOC

+ * expects the ECC to be computed backward, i.e. from the last byte down

+ * to the first one.

+ */

+int nand_calculate_ecc_kw(struct nand_device_s *device, const u8 *data, u8 *ecc)

+{

+	unsigned int r7, r6, r5, r4, r3, r2, r1, r0;

+	int i;

+	static int tables_initialized = 0;

+

+	if (!tables_initialized) {

+		gf_build_log_exp_table();

+		tables_initialized = 1;

+	}

+

+	/*

+	 * Load bytes 504..511 of the data into r.

+	 */

+	r0 = data[504];

+	r1 = data[505];

+	r2 = data[506];

+	r3 = data[507];

+	r4 = data[508];

+	r5 = data[509];

+	r6 = data[510];

+	r7 = data[511];

+

+

+	/*

+	 * Shift bytes 503..0 (in that order) into r0, followed

+	 * by eight zero bytes, while reducing the polynomial by the

+	 * generator polynomial in every step.

+	 */

+	for (i = 503; i >= -8; i--) {

+		unsigned int d;

+

+		d = 0;

+		if (i >= 0)

+			d = data[i];

+

+		if (r7) {

+			u16 *t = gf_exp + gf_log[r7];

+

+			r7 = r6 ^ t[0x21c];

+			r6 = r5 ^ t[0x181];

+			r5 = r4 ^ t[0x18e];

+			r4 = r3 ^ t[0x25f];

+			r3 = r2 ^ t[0x197];

+			r2 = r1 ^ t[0x193];

+			r1 = r0 ^ t[0x237];

+			r0 = d  ^ t[0x024];

+		} else {

+			r7 = r6;

+			r6 = r5;

+			r5 = r4;

+			r4 = r3;

+			r3 = r2;

+			r2 = r1;

+			r1 = r0;

+			r0 = d;

+		}

+	}

+

+	ecc[0] = r0;

+	ecc[1] = (r0 >> 8) | (r1 << 2);

+	ecc[2] = (r1 >> 6) | (r2 << 4);

+	ecc[3] = (r2 >> 4) | (r3 << 6);

+	ecc[4] = (r3 >> 2);

+	ecc[5] = r4;

+	ecc[6] = (r4 >> 8) | (r5 << 2);

+	ecc[7] = (r5 >> 6) | (r6 << 4);

+	ecc[8] = (r6 >> 4) | (r7 << 6);

+	ecc[9] = (r7 >> 2);

+

+	return 0;

+}