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gr-satnogs/lib/ax25_decoder_bm_impl.cc

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/* -*- c++ -*- */
/*
* gr-satnogs: SatNOGS GNU Radio Out-Of-Tree Module
*
* Copyright (C) 2016-2019
* Libre Space Foundation <http://librespacefoundation.org/>
*
* 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 3 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, see <http://www.gnu.org/licenses/>.
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <gnuradio/io_signature.h>
#include <satnogs/log.h>
#include <satnogs/ax25.h>
#include "ax25_decoder_bm_impl.h"
namespace gr
{
namespace satnogs
{
ax25_decoder_bm::sptr
ax25_decoder_bm::make (const std::string &addr, uint8_t ssid, bool promisc,
bool descramble, size_t max_frame_len)
{
return gnuradio::get_initial_sptr (
new ax25_decoder_bm_impl (addr, ssid, promisc, descramble, max_frame_len));
}
/*
* The private constructor
*/
ax25_decoder_bm_impl::ax25_decoder_bm_impl (const std::string &addr,
uint8_t ssid, bool promisc,
bool descramble,
size_t max_frame_len) :
gr::sync_block ("ax25_decoder_bm",
gr::io_signature::make (1, 1, sizeof(uint8_t)),
gr::io_signature::make (0, 0, 0)),
d_promisc (promisc),
d_descramble (descramble),
d_max_frame_len (max_frame_len),
d_state (NO_SYNC),
d_shift_reg (0x0),
d_dec_b (0x0),
d_prev_bit_nrzi (0),
d_received_bytes (0),
d_decoded_bits (0),
d_lfsr (0x21, 0x0, 16),
d_frame_buffer (
new uint8_t[max_frame_len + AX25_MAX_ADDR_LEN + AX25_MAX_CTRL_LEN
+ sizeof(uint16_t)]),
d_start_idx(0)
{
/* Valid PDUs output message port */
message_port_register_out (pmt::mp ("pdu"));
/*
* Valid invalid (wrong CRC, different destination Callsign/SSID,
* wrong frame size)PDUs output message port
*/
message_port_register_out (pmt::mp ("failed_pdu"));
}
void
ax25_decoder_bm_impl::decode ()
{
while (1) {
bool cont = false;
switch (d_state)
{
case NO_SYNC:
for (size_t i = 0; i < d_bitstream.size (); i++) {
decode_1b (d_bitstream[i]);
if (d_shift_reg == AX25_SYNC_FLAG) {
d_bitstream.erase (d_bitstream.begin (),
d_bitstream.begin () + i + 1);
enter_sync_state ();
d_start_idx = 0;
cont = true;
break;
}
}
if(cont) {
continue;
}
d_bitstream.clear ();
return;
case IN_SYNC:
/*
* Most of the transmitters repeat several times the AX.25 SYNC
* In case of G3RUH this is mandatory to allow the self synchronizing
* scrambler to settle
*/
for (size_t i = d_start_idx; i < d_bitstream.size (); i++) {
decode_1b (d_bitstream[i]);
d_decoded_bits++;
if (d_decoded_bits == 8) {
/* Perhaps we are in frame! */
if (d_shift_reg != AX25_SYNC_FLAG) {
d_start_idx = i + 1;
enter_decoding_state ();
cont = true;
break;
}
d_decoded_bits = 0;
}
}
if(cont) {
continue;
}
d_start_idx = d_bitstream.size ();
return;
case DECODING:
for (size_t i = d_start_idx; i < d_bitstream.size (); i++) {
decode_1b (d_bitstream[i]);
if (d_shift_reg == AX25_SYNC_FLAG) {
LOG_DEBUG("Found frame end");
if (enter_frame_end ()) {
d_bitstream.erase (d_bitstream.begin (),
d_bitstream.begin () + i + 1);
}
cont = true;
break;
}
else if ((d_shift_reg & 0xfc) == 0x7c) {
/*This was a stuffed bit */
d_dec_b <<= 1;
}
else if ((d_shift_reg & 0xfe) == 0xfe) {
LOG_DEBUG("Invalid shift register value %u", d_received_bytes);
reset_state ();
cont = true;
break;
}
else {
d_decoded_bits++;
if (d_decoded_bits == 8) {
d_frame_buffer[d_received_bytes++] = d_dec_b;
d_decoded_bits = 0;
/*Check if the frame limit was reached */
if (d_received_bytes >= d_max_frame_len) {
LOG_DEBUG("Wrong size");
reset_state ();
cont = true;
break;
}
}
}
}
if(cont) {
continue;
}
d_start_idx = d_bitstream.size ();
return;
default:
LOG_ERROR("Invalid decoding state");
reset_state ();
return;
}
}
}
/*
* Our virtual destructor.
*/
ax25_decoder_bm_impl::~ax25_decoder_bm_impl ()
{
delete[] d_frame_buffer;
LOG_DEBUG("Left over: %lu", d_bitstream.size());
}
void
ax25_decoder_bm_impl::reset_state ()
{
d_state = NO_SYNC;
d_dec_b = 0x0;
d_shift_reg = 0x0;
d_decoded_bits = 0;
d_received_bytes = 0;
}
void
ax25_decoder_bm_impl::enter_sync_state ()
{
d_state = IN_SYNC;
d_dec_b = 0x0;
d_shift_reg = 0x0;
d_decoded_bits = 0;
d_received_bytes = 0;
}
void
ax25_decoder_bm_impl::enter_decoding_state ()
{
uint8_t tmp;
d_state = DECODING;
d_decoded_bits = 0;
d_received_bytes = 0;
/*
* Due to the possibility of bit stuffing on the first byte some special
* handling is necessary
*/
if ((d_shift_reg & 0xfc) == 0x7c) {
/*This was a stuffed bit */
d_dec_b <<= 1;
d_decoded_bits = 7;
}
else {
d_frame_buffer[0] = d_dec_b;
d_decoded_bits = 0;
d_received_bytes = 1;
}
}
bool
ax25_decoder_bm_impl::enter_frame_end ()
{
uint16_t fcs;
uint16_t recv_fcs = 0x0;
/* First check if the size of the frame is valid */
if (d_received_bytes < AX25_MIN_ADDR_LEN + sizeof(uint16_t)) {
reset_state ();
return false;
}
/*
* Check if the frame is correct using the FCS field
* Using this field also try to correct up to 2 error bits
*/
if (frame_check ()) {
message_port_pub (
pmt::mp ("pdu"),
pmt::make_blob (d_frame_buffer, d_received_bytes - sizeof(uint16_t)));
reset_state ();
return true;
}
else {
message_port_pub (
pmt::mp ("failed_pdu"),
pmt::make_blob (d_frame_buffer, d_received_bytes - sizeof(uint16_t)));
LOG_DEBUG("Wrong crc");
reset_state ();
return false;
}
}
inline void
ax25_decoder_bm_impl::decode_1b (uint8_t in)
{
/* In AX.25 the LS bit is sent first */
d_shift_reg = (d_shift_reg >> 1) | (in << 7);
d_dec_b = (d_dec_b >> 1) | (in << 7);
}
bool
ax25_decoder_bm_impl::frame_check ()
{
uint16_t fcs;
uint16_t recv_fcs = 0x0;
uint8_t orig_byte;
/* Check if the frame is correct using the FCS field */
fcs = ax25_fcs (d_frame_buffer, d_received_bytes - sizeof(uint16_t));
recv_fcs = (((uint16_t) d_frame_buffer[d_received_bytes - 1]) << 8)
| d_frame_buffer[d_received_bytes - 2];
if (fcs == recv_fcs) {
return true;
}
return false;
}
int
ax25_decoder_bm_impl::work (int noutput_items,
gr_vector_const_void_star &input_items,
gr_vector_void_star &output_items)
{
int ret;
const uint8_t *in = (const uint8_t*) input_items[0];
if (noutput_items < 1) {
return noutput_items;
}
if (d_descramble) {
for (int i = 0; i < noutput_items; i++) {
/* Perform NRZI decoding */
uint8_t b = (~((in[i] - d_prev_bit_nrzi) % 2)) & 0x1;
d_prev_bit_nrzi = in[i];
b = d_lfsr.next_bit_descramble (b);
d_bitstream.push_back (b);
}
}
else {
for (int i = 0; i < noutput_items; i++) {
/* Perform NRZI decoding */
uint8_t b = (~((in[i] - d_prev_bit_nrzi) % 2)) & 0x1;
d_prev_bit_nrzi = in[i];
d_bitstream.push_back (b);
}
}
decode();
return noutput_items;
}
} /* namespace satnogs */
} /* namespace gr */
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