130 lines
3.3 KiB
C
130 lines
3.3 KiB
C
/*
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* ISO14443A modified Miller decoder for OpenPICC
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* (C) 2006 by Harald Welte <hwelte@hmw-consulting.de>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*
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*/
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/*
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* LSB First LSB hex
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* Sequence X 0010 0100 0x4
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* Sequence Y 0000 0000 0x0
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* Sequence Z 1000 0001 0x1
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*
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* Logic 1 Sequence X
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* Logic 0 Sequence Y with two exceptions:
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* - if there are more contiguous 0, Z used from second one
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* - if the first bit after SOF is 0, sequence Z used for all contig 0's
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* SOF Sequence Z
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* EOF Logic 0 followed by Sequence Y
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*
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* cmd hex bits symbols hex (quad-sampled)
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*
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* REQA 0x26 S 0110010 E Z ZXXYZXY ZY 0x10410441
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* WUPA 0x52 S 0100101 E Z ZXYZXYX YY 0x04041041
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*
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* SOF is 'eaten' by SSC start condition (Compare 0). Remaining bits are
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* mirrored, e.g. samples for LSB of first byte are & 0xf
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*
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*/
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#include <sys/types.h>
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#include <os/dbgu.h>
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#include <picc/decoder.h>
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#define OVERSAMPLING_RATE 4
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/* definitions for four-times oversampling */
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#define SEQ_X 0x4
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#define SEQ_Y 0x0
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#define SEQ_Z 0x1
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/* decode a single sampled bit */
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static uint8_t miller_decode_sampled_bit(uint32_t sampled_bit)
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{
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switch (sampled_bit) {
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case SEQ_X:
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return 1;
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break;
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case SEQ_Z:
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case SEQ_Y:
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return 0;
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break;
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default:
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DEBUGP("unknown sequence sample `%x' ", sampled_bit);
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return 2;
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break;
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}
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}
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/* decode a single 32bit data sample of an 8bit miller encoded word */
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static int miller_decode_sample(uint32_t sample, uint8_t *data)
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{
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uint8_t ret = 0;
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unsigned int i;
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for (i = 0; i < sizeof(sample)/OVERSAMPLING_RATE; i++) {
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uint8_t bit = miller_decode_sampled_bit(sample & 0xf);
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if (bit == 1)
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ret |= 1;
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/* else do nothing since ret was initialized with 0 */
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/* skip shifting in case of last data bit */
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if (i == sizeof(sample)/OVERSAMPLING_RATE)
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break;
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sample = sample >> OVERSAMPLING_RATE;
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ret = ret << 1;
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}
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*data = ret;
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return ret;
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}
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static uint32_t get_next_bytesample(struct decoder_state *ms,
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uint8_t *parity_sample)
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{
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uint32_t ret = 0;
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/* get remaining bits from the current word */
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ret = *(ms->buf32) >> ms->bit_ofs;
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/* move to next word */
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ms->buf32++;
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/* if required, get remaining bits from next word */
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if (ms->bit_ofs)
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ret |= *(ms->buf32) << (32 - ms->bit_ofs);
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*parity_sample = (*(ms->buf32) >> ms->bit_ofs & 0xf);
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/* increment bit offset (modulo 32) */
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ms->bit_ofs = (ms->bit_ofs + OVERSAMPLING_RATE) % 32;
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return ret;
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}
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static struct decoder_algo miller_decoder = {
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.oversampling_rate = OVERSAMPLING_RATE,
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.bits_per_sampled_char = 9 * OVERSAMPLING_RATE,
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.bytesample_mask = 0xffffffff,
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.decode_sample = &miller_decode_sample,
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.get_next_bytesample = &get_next_bytesample,
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};
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