From 29ea5bbf5b9c3b3679aa40e4ee7029284cb424c6 Mon Sep 17 00:00:00 2001
From: henryk <henryk@6dc7ffe9-61d6-0310-9af1-9938baff3ed1>
Date: Sat, 24 Nov 2007 07:59:42 +0000
Subject: Add load modulation and encoding/decoding code from harald

git-svn-id: https://svn.openpcd.org:2342/trunk@351 6dc7ffe9-61d6-0310-9af1-9938baff3ed1
---
 openpicc/application/decoder_miller.c | 130 ++++++++++++++++++++++++++++++++++
 1 file changed, 130 insertions(+)
 create mode 100644 openpicc/application/decoder_miller.c

(limited to 'openpicc/application/decoder_miller.c')

diff --git a/openpicc/application/decoder_miller.c b/openpicc/application/decoder_miller.c
new file mode 100644
index 0000000..aa3a669
--- /dev/null
+++ b/openpicc/application/decoder_miller.c
@@ -0,0 +1,130 @@
+/* 
+ * ISO14443A modified Miller decoder for OpenPICC
+ * (C) 2006 by Harald Welte <hwelte@hmw-consulting.de>
+ *
+ *  This program 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 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program 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 program; if not, write to the Free Software
+ *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ */
+
+/*
+ * 		LSB First	LSB 	hex
+ * Sequence X	0010		0100	0x4
+ * Sequence Y	0000		0000	0x0
+ * Sequence Z	1000		0001	0x1
+ *
+ * Logic 1	Sequence X
+ * Logic 0	Sequence Y with two exceptions:
+ * 		- if there are more contiguous 0, Z used from second one
+ * 		- if the first bit after SOF is 0, sequence Z used for all contig 0's
+ * SOF		Sequence Z
+ * EOF		Logic 0 followed by Sequence Y
+ *
+ * cmd	   hex	   bits            symbols              hex (quad-sampled)
+ *
+ * REQA    0x26    S 0110010 E     Z ZXXYZXY ZY		0x10410441
+ * WUPA    0x52    S 0100101 E     Z ZXYZXYX YY		0x04041041
+ *
+ * SOF is 'eaten' by SSC start condition (Compare 0). Remaining bits are
+ * mirrored, e.g. samples for LSB of first byte are & 0xf
+ *
+ */
+
+#include <sys/types.h>
+
+#include "openpicc.h"
+#include "dbgu.h"
+#include "decoder.h"
+
+
+#define OVERSAMPLING_RATE	4
+
+/* definitions for four-times oversampling */
+#define SEQ_X	0x4
+#define SEQ_Y	0x0
+#define SEQ_Z	0x1
+
+/* decode a single sampled bit */
+static u_int8_t miller_decode_sampled_bit(u_int32_t sampled_bit)
+{
+	switch (sampled_bit) {
+	case SEQ_X:
+		return 1;
+		break;
+	case SEQ_Z:
+	case SEQ_Y:
+		return 0;
+		break;
+	default:
+		DEBUGP("unknown sequence sample `%x' ", sampled_bit);
+		return 2;
+		break;
+	}
+}
+
+/* decode a single 32bit data sample of an 8bit miller encoded word */
+static int miller_decode_sample(u_int32_t sample, u_int8_t *data)
+{
+	u_int8_t ret = 0;
+	unsigned int i;
+
+	for (i = 0; i < sizeof(sample)/OVERSAMPLING_RATE; i++) {
+		u_int8_t bit = miller_decode_sampled_bit(sample & 0xf);
+
+		if (bit == 1)
+			ret |= 1;
+		/* else do nothing since ret was initialized with 0 */
+
+		/* skip shifting in case of last data bit */
+		if (i == sizeof(sample)/OVERSAMPLING_RATE)
+			break;
+
+		sample = sample >> OVERSAMPLING_RATE;
+		ret = ret << 1;
+	}
+
+	*data = ret;
+
+	return ret;
+}
+
+static u_int32_t get_next_bytesample(struct decoder_state *ms,
+				     u_int8_t *parity_sample)
+{
+	u_int32_t ret = 0;
+
+	/* get remaining bits from the current word */
+	ret = *(ms->buf32) >> ms->bit_ofs;
+	/* move to next word */
+	ms->buf32++;
+
+	/* if required, get remaining bits from next word */
+	if (ms->bit_ofs)
+		ret |= *(ms->buf32) << (32 - ms->bit_ofs);
+	
+	*parity_sample = (*(ms->buf32) >> ms->bit_ofs & 0xf);
+
+	/* increment bit offset (modulo 32) */
+	ms->bit_ofs = (ms->bit_ofs + OVERSAMPLING_RATE) % 32;
+
+	return ret;
+}
+
+struct decoder_algo miller_decoder = {
+	.oversampling_rate = OVERSAMPLING_RATE,
+	.bits_per_sampled_char = 9 * OVERSAMPLING_RATE,
+	.bytesample_mask = 0xffffffff,
+	.decode_sample = &miller_decode_sample,
+	.get_next_bytesample = &get_next_bytesample,
+};
-- 
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