476 lines
14 KiB
C++
476 lines
14 KiB
C++
/* -*- c++ -*- */
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/*
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* gr-satnogs: SatNOGS GNU Radio Out-Of-Tree Module
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*
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* Copyright (C) 2016, 2017, 2018
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* Libre Space Foundation <http://librespacefoundation.org/>
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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 3 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, see <http://www.gnu.org/licenses/>.
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*/
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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include <gnuradio/io_signature.h>
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#include <satnogs/log.h>
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#include <satnogs/ax25.h>
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#include "ax25_decoder_bm_impl.h"
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namespace gr
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{
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namespace satnogs
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{
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ax25_decoder_bm::sptr
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ax25_decoder_bm::make (const std::string& addr, uint8_t ssid, bool promisc,
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bool descramble, size_t max_frame_len)
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{
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return gnuradio::get_initial_sptr (
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new ax25_decoder_bm_impl (addr, ssid, promisc, descramble,
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max_frame_len));
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}
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/*
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* The private constructor
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*/
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ax25_decoder_bm_impl::ax25_decoder_bm_impl (const std::string& addr,
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uint8_t ssid, bool promisc,
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bool descramble,
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size_t max_frame_len) :
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gr::sync_block ("ax25_decoder_bm",
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gr::io_signature::make (1, 1, sizeof(uint8_t)),
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gr::io_signature::make (0, 0, 0)),
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d_promisc (promisc),
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d_descramble (descramble),
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d_max_frame_len (max_frame_len),
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d_state (NO_SYNC),
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d_shift_reg (0x0),
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d_dec_b (0x0),
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d_prev_bit_nrzi (0),
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d_received_bytes (0),
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d_decoded_bits (0),
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d_lfsr (0x21, 0x0, 16),
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d_frame_buffer (
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new uint8_t[max_frame_len + AX25_MAX_ADDR_LEN
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+ AX25_MAX_CTRL_LEN + sizeof(uint16_t)])
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{
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/* Valid PDUs output message port */
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message_port_register_out (pmt::mp ("pdu"));
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/*
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* Valid invalid (wrong CRC, different destination Callsign/SSID,
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* wrong frame size)PDUs output message port
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*/
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message_port_register_out (pmt::mp ("failed_pdu"));
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}
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size_t
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ax25_decoder_bm_impl::descramble_and_decode (const uint8_t* in,
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size_t nitems)
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{
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size_t i;
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uint8_t descr_bit;
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uint8_t dec_bit;
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switch (d_state)
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{
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case NO_SYNC:
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for (i = 0; i < nitems; i++) {
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descramble_and_decode_1b (in[i]);
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if (d_shift_reg == AX25_SYNC_FLAG) {
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enter_sync_state ();
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return i + 1;
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}
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}
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return nitems;
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case IN_SYNC:
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/*
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* Most of the transmitters repeat several times the AX.25 SYNC
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* In case of G3RUH this is mandatory to allow the self synchronizing
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* scrambler to settle
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*/
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for (i = 0; i < nitems; i++) {
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descramble_and_decode_1b (in[i]);
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d_decoded_bits++;
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if(d_decoded_bits == 8) {
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/* Perhaps we are in frame! */
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if(d_shift_reg != AX25_SYNC_FLAG) {
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enter_decoding_state();
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return i+1;
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}
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d_decoded_bits = 0;
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}
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}
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return nitems;
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case DECODING:
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for (i = 0; i < nitems; i++) {
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descramble_and_decode_1b (in[i]);
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if (d_shift_reg == AX25_SYNC_FLAG) {
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LOG_DEBUG("Found frame end");
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enter_frame_end();
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return i+1;
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}
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else if ((d_shift_reg & 0xfc) == 0x7c) {
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/*This was a stuffed bit */
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d_dec_b <<= 1;
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}
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else if((d_shift_reg & 0xfe) == 0xfe) {
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LOG_DEBUG("Invalid shift register value %u", d_received_bytes);
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reset_state ();
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return i+1;
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}
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else{
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d_decoded_bits++;
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if(d_decoded_bits == 8) {
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/* Check if the received byte is valid */
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if(!check_byte()) {
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reset_state ();
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return i + 1;
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}
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d_frame_buffer[d_received_bytes] = d_dec_b;
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d_received_bytes++;
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d_decoded_bits = 0;
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/*Check if the frame limit was reached */
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if (d_received_bytes >= d_max_frame_len) {
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LOG_DEBUG("Wrong size");
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message_port_pub (
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pmt::mp ("failed_pdu"),
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pmt::make_blob (d_frame_buffer, d_max_frame_len));
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reset_state ();
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return i+1;
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}
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}
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}
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}
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return nitems;
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case FRAME_END:
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for (i = 0; i < nitems; i++) {
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descramble_and_decode_1b (in[i]);
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d_decoded_bits++;
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if (d_decoded_bits == 8) {
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/* Repetitions of the trailing SYNC flag finished */
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if (d_shift_reg != AX25_SYNC_FLAG) {
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reset_state();
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return i + 1;
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}
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d_decoded_bits = 0;
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}
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}
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return nitems;
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default:
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LOG_ERROR("Invalid decoding state");
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reset_state();
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return nitems;
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}
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}
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size_t
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ax25_decoder_bm_impl::decode (const uint8_t* in, size_t nitems)
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{
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size_t i;
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uint8_t descr_bit;
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uint8_t dec_bit;
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switch (d_state)
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{
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case NO_SYNC:
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for (i = 0; i < nitems; i++) {
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decode_1b (in[i]);
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if (d_shift_reg == AX25_SYNC_FLAG) {
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enter_sync_state ();
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return i + 1;
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}
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}
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return nitems;
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case IN_SYNC:
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/*
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* Most of the transmitters repeat several times the AX.25 SYNC
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* In case of G3RUH this is mandatory to allow the self synchronizing
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* scrambler to settle
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*/
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for (i = 0; i < nitems; i++) {
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decode_1b (in[i]);
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d_decoded_bits++;
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if (d_decoded_bits == 8) {
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/* Perhaps we are in frame! */
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if (d_shift_reg != AX25_SYNC_FLAG) {
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enter_decoding_state ();
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return i + 1;
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}
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d_decoded_bits = 0;
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}
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}
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return nitems;
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case DECODING:
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for (i = 0; i < nitems; i++) {
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decode_1b (in[i]);
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if (d_shift_reg == AX25_SYNC_FLAG) {
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enter_frame_end ();
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return i + 1;
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}
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else if ((d_shift_reg & 0xfc) == 0x7c) {
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/*This was a stuffed bit */
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d_dec_b <<= 1;
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}
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else if ((d_shift_reg & 0xfe) == 0xfe) {
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LOG_DEBUG("Invalid shift register value");
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reset_state ();
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return i + 1;
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}
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else {
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d_decoded_bits++;
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if (d_decoded_bits == 8) {
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/* Check if the received byte is valid */
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if(!check_byte()) {
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reset_state ();
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return i + 1;
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}
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d_frame_buffer[d_received_bytes] = d_dec_b;
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d_received_bytes++;
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d_decoded_bits = 0;
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/*Check if the frame limit was reached */
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if (d_received_bytes >= d_max_frame_len) {
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LOG_DEBUG("Wrong size");
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message_port_pub (
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pmt::mp ("failed_pdu"),
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pmt::make_blob (d_frame_buffer, d_max_frame_len));
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reset_state ();
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return i + 1;
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}
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}
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}
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}
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return nitems;
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case FRAME_END:
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for (i = 0; i < nitems; i++) {
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decode_1b (in[i]);
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d_decoded_bits++;
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if (d_decoded_bits == 8) {
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/* Repetitions of the trailing SYNC flag finished */
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if (d_shift_reg != AX25_SYNC_FLAG) {
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reset_state ();
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return i + 1;
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}
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d_decoded_bits = 0;
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}
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}
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return nitems;
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default:
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LOG_ERROR("Invalid decoding state");
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reset_state ();
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return nitems;
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}
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}
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/*
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* Our virtual destructor.
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*/
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ax25_decoder_bm_impl::~ax25_decoder_bm_impl ()
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{
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delete [] d_frame_buffer;
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}
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void
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ax25_decoder_bm_impl::reset_state ()
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{
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d_state = NO_SYNC;
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d_dec_b = 0x0;
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d_shift_reg = 0x0;
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d_decoded_bits = 0;
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d_received_bytes = 0;
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d_prev_bit_nrzi = 0;
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}
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void
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ax25_decoder_bm_impl::enter_sync_state ()
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{
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d_state = IN_SYNC;
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d_dec_b = 0x0;
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d_shift_reg = 0x0;
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d_decoded_bits = 0;
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d_received_bytes = 0;
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}
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void
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ax25_decoder_bm_impl::enter_decoding_state ()
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{
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uint8_t tmp;
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d_state = DECODING;
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d_decoded_bits = 0;
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d_shift_reg = 0x0;
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/*
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* Due to the possibility of bit stuffing on the first byte some special
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* handling is necessary
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*/
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tmp = d_dec_b;
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d_dec_b = 0x0;
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for (size_t i = 0; i < 8; i++) {
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d_shift_reg = (d_shift_reg >> 1) | (((tmp >> i) & 0x1) << 7);
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d_dec_b = (d_dec_b >> 1) | (((tmp >> i) & 0x1) << 7);
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if ((d_shift_reg & 0xfc) == 0x7c) {
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/*This was a stuffed bit */
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d_dec_b <<= 1;
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}
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else{
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d_decoded_bits++;
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}
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}
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if(d_decoded_bits == 8) {
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d_frame_buffer[0] = d_dec_b;
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d_decoded_bits = 0;
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d_received_bytes = 1;
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}
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else {
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d_received_bytes = 0;
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}
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}
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void
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ax25_decoder_bm_impl::enter_frame_end ()
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{
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uint16_t fcs;
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uint16_t recv_fcs = 0x0;
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/* First check if the size of the frame is valid */
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if (d_received_bytes < AX25_MIN_ADDR_LEN + sizeof(uint16_t)) {
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d_dec_b = 0x0;
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d_shift_reg = 0x0;
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d_decoded_bits = 0;
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d_received_bytes = 0;
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d_state = FRAME_END;
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return;
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}
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/* Check if the frame is correct using the FCS field */
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fcs = ax25_fcs (d_frame_buffer, d_received_bytes - sizeof(uint16_t));
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recv_fcs = (((uint16_t) d_frame_buffer[d_received_bytes - 1]) << 8)
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| d_frame_buffer[d_received_bytes - 2];
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if (fcs == recv_fcs) {
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message_port_pub (
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pmt::mp ("pdu"),
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pmt::make_blob (d_frame_buffer,
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d_received_bytes - sizeof(uint16_t)));
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}
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else {
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message_port_pub (
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pmt::mp ("failed_pdu"),
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pmt::make_blob (d_frame_buffer,
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d_received_bytes - sizeof(uint16_t)));
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LOG_DEBUG("Wrong crc");
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}
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d_dec_b = 0x0;
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d_shift_reg = 0x0;
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d_decoded_bits = 0;
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d_received_bytes = 0;
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d_state = FRAME_END;
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}
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/**
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* Performs descrambling and NRZI decoding of an input bit.
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* The decoded bit is then shifted in front of the d_shift_reg and the d_dec_b
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* variables. This shift in front is due to the LS bit first transmission
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* of the Ax.25 protocol.
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*
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* @param in input bit
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*/
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inline void
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ax25_decoder_bm_impl::descramble_and_decode_1b (uint8_t in)
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{
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uint8_t descr_bit;
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uint8_t dec_bit;
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in &= 0x1;
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/* Perform NRZI decoding */
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dec_bit = (~((in - d_prev_bit_nrzi) % 2)) & 0x1;
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d_prev_bit_nrzi = in;
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/* Descramble the input bit */
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descr_bit = d_lfsr.next_bit_descramble (dec_bit);
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/* In AX.25 the LS bit is sent first */
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d_shift_reg = (d_shift_reg >> 1) | (descr_bit << 7);
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d_dec_b = (d_dec_b >> 1) | (descr_bit << 7);
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}
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inline void
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ax25_decoder_bm_impl::decode_1b (uint8_t in)
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{
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uint8_t dec_bit;
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in &= 0x1;
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/* Perform NRZI decoding */
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dec_bit = (~((in - d_prev_bit_nrzi) % 2)) & 0x1;
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d_prev_bit_nrzi = in;
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/* In AX.25 the LS bit is sent first */
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d_shift_reg = (d_shift_reg >> 1) | (dec_bit << 7);
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d_dec_b = (d_dec_b >> 1) | (dec_bit << 7);
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}
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/**
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* Checks if a AX.25 decoded byte is valid. This actually can be checked
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* only in the address field, where all fields should have the LS bit
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* set to zero.
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* @returns true if the decoded byte is valid, false otherwise
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*/
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inline bool
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ax25_decoder_bm_impl::check_byte ()
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{
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if(d_received_bytes < AX25_MIN_ADDR_LEN - 1) {
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if(d_dec_b & 0x1) {
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return false;
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}
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}
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else if(d_received_bytes == AX25_MIN_ADDR_LEN - 1) {
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if(d_dec_b & 0x1) {
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return true;
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}
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return false;
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}
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return true;
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}
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int
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ax25_decoder_bm_impl::work (int noutput_items,
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gr_vector_const_void_star &input_items,
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gr_vector_void_star &output_items)
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{
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int ret;
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const uint8_t *in = (const uint8_t *) input_items[0];
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if(noutput_items < 1) {
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return noutput_items;
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}
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if (d_descramble) {
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ret = descramble_and_decode (in, noutput_items);
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}
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else {
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ret = decode (in, noutput_items);
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}
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return ret;
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}
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} /* namespace satnogs */
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} /* namespace gr */
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