portapack-mayhem/firmware/baseband/proc_adsbrx.cpp
furrtek 5a67a7080a ADS-B TX works well enough for dump1090 and gr-air-modes
Hooked ADS-B RX to baseband instead of debug IQ file, not tested
2017-07-23 12:20:32 +01:00

159 lines
4.1 KiB
C++

/*
* 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;
float mag;
uint32_t c;
uint8_t level, bit, byte;
bool confidence, first_in_window, last_in_window;
// 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 = buffer.p[i].real();
im = buffer.p[i].imag();
mag = __builtin_sqrtf((re * re) + (im * im)) * k;
// Only used for preamble detection and visualisation
level = (mag < 0.3) ? 0 : // Blank weak signals
(mag > prev_mag) ? 1 : 0;
if (decoding) {
// Decode
// 1 bit lasts 2 samples
if (sample_count & 1) {
if ((prev_mag < threshold_low) && (mag < threshold_low)) {
// Both under window, silence.
if (null_count > 3) {
//text_debug_b.set("Bits:" + bits.substr(0, 25));
//text_debug_c.set("Hex:" + hex_str.substr(0, 26));
//text_debug_d.set("DF=" + to_string_dec_uint(frame.get_DF()) + " ICAO=" + to_string_hex(frame.get_ICAO_address(), 6));
const ADSBFrameMessage message(frame);
shared_memory.application_queue.push(message);
decoding = false;
} else
null_count++;
confidence = false;
if (prev_mag > mag)
bit = 1;
else
bit = 0;
} else {
null_count = 0;
first_in_window = ((prev_mag >= threshold_low) && (prev_mag <= threshold_high));
last_in_window = ((mag >= threshold_low) && (mag <= threshold_high));
if ((first_in_window && !last_in_window) || (!first_in_window && last_in_window)) {
confidence = true;
if (prev_mag > mag)
bit = 1;
else
bit = 0;
} else {
confidence = false;
if (prev_mag > mag)
bit = 1;
else
bit = 0;
}
}
byte = bit | (byte << 1);
bit_count++;
if (!(bit_count & 7)) {
// Got one byte
frame.push_byte(byte);
}
}
sample_count++;
} else {
// Look for preamble
// Shift
for (c = 0; c < (ADSB_PREAMBLE_LENGTH - 1); c++)
shifter[c] = shifter[c + 1];
shifter[15] = std::make_pair(mag, level);
// Compare
for (c = 0; c < ADSB_PREAMBLE_LENGTH; c++) {
if (shifter[c].second != adsb_preamble[c])
break;
}
if (c == ADSB_PREAMBLE_LENGTH) {
decoding = true;
sample_count = 0;
null_count = 0;
bit_count = 0;
frame.clear();
// Compute preamble pulses power to set thresholds
threshold = (shifter[0].first + shifter[2].first + shifter[7].first + shifter[9].first) / 4;
threshold_high = threshold * 1.414; // +3dB
threshold_low = threshold * 0.707; // -3dB
}
}
prev_mag = mag;
}
}
void ADSBRXProcessor::on_message(const Message* const message) {
if (message->id == Message::ID::ADSBConfigure) {
null_count = 0;
bit_count = 0;
sample_count = 0;
decoding = false;
configured = true;
}
}
int main() {
EventDispatcher event_dispatcher { std::make_unique<ADSBRXProcessor>() };
event_dispatcher.run();
return 0;
}