/* 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, };