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/* NRZ-L decoder implementation 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

 *

 */

/*

 * speed(kbps)	106	212	424	848

 * etu		128/fc	64/fc	32/fc	16/fc

 * etu(usec)	9.4	4.7	2.35	1.18

 *

 * NRZ-L coding with logic level

 *

 * logic 1:	carrier high field amplitude (no modulation)

 * logic 0:	carrier low field amplitude

 *

 * Character transmission format:

 *	start bit:	logic 0

 *	data:		eight bits, lsb first

 *	stop bit	logic 1

 *

 * Frame Format:

 *

 * 		SOF char [EGT char, ...] EOF

 *

 * 	SOF: falling edge, 10..11 etu '0', rising edge in 1etu, 2..3etu '1'

 *	EGT: between 0 and 57uS 

 *	EOF: falling edge, 10..11 etu '0', rising edge in 1etu

 *

 *

 * Sampling

 * - sample once per bit clock, exactly in the middle of it

 * - synchronize CARRIER_DIV TC0 to first falling edge

 * - Configure CARRIER_DIV RA compare (rising edge) to be at

 *   etu/2 carrier clocks.

 * - problem: SOF 12..14etu length, therefore we cannot specify

 *            SOF as full start condition and then sample with 10bit

 *            frames :(

 * 

 */

#include <errno.h>

#include <sys/types.h>

#include "openpicc.h"

#include "dbgu.h"

#include "decoder.h"

/* currently this code will only work with oversampling_rate == 1 */

#define OVERSAMPLING_RATE 1

static u_int32_t get_next_bytesample(struct decoder_state *st,

				     u_int8_t *parity_sample)

{

	u_int32_t ret = 0;

	u_int8_t bits_per_sampled_char = st->algo->bits_per_sampled_char;

	u_int8_t bytesample_mask = st->algo->bytesample_mask;

	/* FIXME: shift start and stop bit into parity_sample and just

	 * return plain 8-bit data word */

	 (void)parity_sample;

	/* first part of 10-databit bytesample */

	ret = (*(st->buf32) >> st->bit_ofs) & bytesample_mask;

	if (st->bit_ofs > 32 - bits_per_sampled_char) {

		/* second half of 10-databit bytesample */

		st->buf32++;

		ret |= (*(st->buf32) << (32 - st->bit_ofs));

	}

	st->bit_ofs = (st->bit_ofs + bits_per_sampled_char) % 32;

	return ret & bytesample_mask;

}

static int nrzl_decode_sample(const u_int32_t sample, u_int8_t *data)

{

	*data = (sample >> 1) & 0xff;

	if (!(sample & 0x01)) {

		DEBUGPCRF("invalid start bit 0!");

		return -EIO;

	}

	if (sample & 0x20) {

		DEBUGPCRF("invalid stop bit 1!");

		return -EIO;

	}

	return 0;

}

struct decoder_algo nrzl_decoder = {

	.oversampling_rate = OVERSAMPLING_RATE,

	.bits_per_sampled_char = 10 * OVERSAMPLING_RATE,

	.bytesample_mask = 0x3ff,

	.decode_sample = &nrzl_decode_sample,

	.get_next_bytesample = &get_next_bytesample,

};