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/* 

 * 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"

/* definitions for four-times oversampling */

#define SEQ_X	0x4

#define SEQ_Y	0x0

#define SEQ_Z	0x1

#define OVERSAMPLING_RATE	2

#define SEQ_X   0x2

#define SEQ_Y   0x0

#define SEQ_Z   0x1

#endif

/* decode a single 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,

};