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Diffstat (limited to 'openpicc/application/decoder_miller.c')
| -rw-r--r-- | openpicc/application/decoder_miller.c | 130 |
1 files changed, 130 insertions, 0 deletions
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, +}; |