190 lines
4.6 KiB
C++
190 lines
4.6 KiB
C++
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/* -*- 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, 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 "ax25_decoder_b_impl.h"
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#include <satnogs/log.h>
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namespace gr {
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namespace satnogs {
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ax25_decoder_b::sptr
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ax25_decoder_b::make(std::string addr, uint8_t ssid, bool promisc)
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{
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return gnuradio::get_initial_sptr
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(new ax25_decoder_b_impl(addr, ssid, promisc));
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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_b_impl::ax25_decoder_b_impl (std::string addr, uint8_t ssid,
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bool promisc) :
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gr::sync_block ("ax25_decoder_b",
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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_state(NO_SYNC),
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d_dec_b(0),
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d_prev_bit(0),
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d_received_bytes(0),
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d_decoded_bits(0),
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d_cont_1(0),
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d_frame_buffer(new uint8_t[AX25_MAX_FRAME_LEN
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+ AX25_MAX_ADDR_LEN
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+ AX25_MAX_CTRL_LEN
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+ sizeof(uint16_t)])
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{
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message_port_register_out (pmt::mp ("pdu"));
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}
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void
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ax25_decoder_b_impl::reset_state ()
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{
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d_state = NO_SYNC;
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d_dec_b = 0;
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d_decoded_bits = 0;
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d_received_bytes = 0;
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d_cont_1 = 0;
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}
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void
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ax25_decoder_b_impl::enter_sync_state ()
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{
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d_state = IN_SYNC;
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d_dec_b = 0;
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d_decoded_bits = 0;
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d_received_bytes = 0;
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d_prev_bit = 0;
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d_cont_1 = 0;
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}
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void
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ax25_decoder_b_impl::update_recv_frame (uint8_t byte)
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{
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uint16_t fcs;
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uint16_t recv_fcs = 0x0;
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if( d_decoded_bits ) {
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return;
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}
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if(byte == AX25_SYNC_FLAG) {
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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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reset_state();
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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 - 2]) << 8)
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| d_frame_buffer[d_received_bytes - 1];
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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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LOG_WARN("Wrong FCS: Should be 0%x, computed as 0%x", recv_fcs, fcs);
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}
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LOG_WARN("Frame size %lu", d_received_bytes);
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reset_state();
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}
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else{
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d_frame_buffer[d_received_bytes++] = byte;
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if(d_received_bytes > AX25_MAX_FRAME_LEN){
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LOG_WARN("Maximum frame size reached. Abort decoding this frame");
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reset_state();
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}
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}
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d_dec_b = 0;
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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_b_impl::~ax25_decoder_b_impl()
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{
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delete[] d_frame_buffer;
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}
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int
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ax25_decoder_b_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 i;
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const uint8_t *in = (const uint8_t *) input_items[0];
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for (i = 0; i < noutput_items; i++) {
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switch (d_state)
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{
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case NO_SYNC:
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d_dec_b = (d_dec_b << 1) | in[i];
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/*
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* If the decoder find the sync flag of the AX.25 frame start the
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* decoding process
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*/
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if(d_dec_b == AX25_SYNC_FLAG){
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enter_sync_state();
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}
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break;
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case IN_SYNC:
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if(in[i]){
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if(d_prev_bit) {
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d_cont_1++;
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}
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else {
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d_cont_1 = 1;
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}
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d_dec_b |= 1 << d_decoded_bits;
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d_decoded_bits = (d_decoded_bits + 1) % 8;
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update_recv_frame(d_dec_b);
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d_prev_bit = 1;
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}
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else{
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/* Check if this a stuffed zero bit */
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if(d_cont_1 < 5) {
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d_decoded_bits = (d_decoded_bits + 1) % 8;
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update_recv_frame(d_dec_b);
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}
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d_prev_bit = 0;
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d_cont_1 = 0;
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}
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break;
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default:
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LOG_ERROR("Invalid decoding state");
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}
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}
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return noutput_items;
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}
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} /* namespace satnogs */
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} /* namespace gr */
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