From 29ea5bbf5b9c3b3679aa40e4ee7029284cb424c6 Mon Sep 17 00:00:00 2001 From: henryk 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_nrzl.c | 111 ++++++++++++++++++++++++++++++++++++ 1 file changed, 111 insertions(+) create mode 100644 openpicc/application/decoder_nrzl.c (limited to 'openpicc/application/decoder_nrzl.c') diff --git a/openpicc/application/decoder_nrzl.c b/openpicc/application/decoder_nrzl.c new file mode 100644 index 0000000..6ffbb45 --- /dev/null +++ b/openpicc/application/decoder_nrzl.c @@ -0,0 +1,111 @@ +/* NRZ-L decoder implementation for OpenPICC + * (C) 2006 by Harald Welte + * + * 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 +#include + +#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, +}; -- cgit v1.2.3