portapack-mayhem/firmware/baseband/proc_adsbrx.cpp

162 lines
5.6 KiB
C++
Raw Normal View History

/*
* Copyright (C) 2014 Jared Boone, ShareBrained Technology, Inc.
* Copyright (C) 2017 Furrtek
*
* This file is part of PortaPack.
*
* 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, 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; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
#include "proc_adsbrx.hpp"
#include "portapack_shared_memory.hpp"
#include "sine_table_int8.hpp"
#include "event_m4.hpp"
#include <cstdint>
#include <cstddef>
using namespace adsb;
void ADSBRXProcessor::execute(const buffer_c8_t& buffer) {
int8_t re, im;
uint32_t mag;
uint32_t c;
uint8_t bit, byte{};
// This is called at 2M/2048 = 977Hz
// One pulse = 500ns = 2 samples
// One bit = 2 pulses = 1us = 4 samples
if (!configured) return;
for (size_t i = 0; i < buffer.count; i++) {
// Compute sample's magnitude
re = (int32_t)buffer.p[i].real();
im = (int32_t)buffer.p[i].imag();
mag = ((uint32_t)(re * re) + (uint32_t)(im * im));
if (decoding) {
// Decode
// 1 bit lasts 2 samples
if (sample_count & 1) {
if (bit_count >= msgLen) {
const ADSBFrameMessage message(frame, amp);
shared_memory.application_queue.push(message);
decoding = false;
bit = (prev_mag > mag) ? 1 : 0;
} else {
bit = (prev_mag > mag) ? 1 : 0;
}
byte = bit | (byte << 1);
bit_count++;
// Perform checks at the end of the first byte
if (!(bit_count & 7)) {
// Store the byte
frame.push_byte(byte);
// Check at the end of the first byte of the message
uint8_t df = (byte >> 3);
if ((bit_count == 8) && !(df & 0x10)) {
msgLen = 56; // DFs 16 or greater are long 112. DFs 15 or less are short 56.
}
// Abondon all frames that arent DF17 or DF18 extended squitters
if ((bit_count == 8) && !((df == 17) || (df == 18))) {
decoding = false;
bit = (prev_mag > mag) ? 1 : 0;
frame.clear();
}
} // last bit of a byte
} // Second sample of each bit
sample_count++;
}
// Continue looking for preamble even if in a packet
// switch if new preamble is higher magnitude
// Shift the preamble
for (c = 0; c < (ADSB_PREAMBLE_LENGTH); c++) {
shifter[c] = shifter[c + 1];
}
shifter[ADSB_PREAMBLE_LENGTH] = mag;
// First check of relations between the first 10 samples
// representing a valid preamble. We don't even investigate further
// if this simple test is not passed
if (shifter[0] < shifter[1] &&
shifter[1] > shifter[2] &&
shifter[2] < shifter[3] &&
shifter[3] > shifter[4] &&
shifter[4] < shifter[1] &&
shifter[5] < shifter[1] &&
shifter[6] < shifter[1] &&
shifter[7] < shifter[1] &&
shifter[8] > shifter[9] &&
shifter[9] < shifter[10] &&
shifter[10] > shifter[11]) {
// The samples between the two spikes must be < than the average
// of the high spikes level. We don't test bits too near to
// the high levels as signals can be out of phase so part of the
// energy can be in the near samples
int32_t thisAmp = (shifter[1] + shifter[3] + shifter[8] + shifter[10]);
uint32_t high = thisAmp / 9;
if (
shifter[5] < high &&
shifter[6] < high &&
// Similarly samples in the range 11-13 must be low, as it is the
// space between the preamble and real data. Again we don't test
// bits too near to high levels, see above
shifter[12] < high &&
shifter[13] < high &&
shifter[14] < high) {
if ((decoding == false) || // New preamble
((decoding == true) && (thisAmp > amp))) // Higher power than existing packet
{
decoding = true;
msgLen = 112;
amp = thisAmp;
sample_count = 0;
bit_count = 0;
frame.clear();
}
} // 4 & 5 low and 11-14 low
} // Check for preamble pattern
// Store mag for next time
prev_mag = mag;
}
}
void ADSBRXProcessor::on_message(const Message* const message) {
if (message->id == Message::ID::ADSBConfigure) {
bit_count = 0;
sample_count = 0;
decoding = false;
configured = true;
}
}
#ifndef _WIN32
int main() {
EventDispatcher event_dispatcher{std::make_unique<ADSBRXProcessor>()};
event_dispatcher.run();
return 0;
}
#endif