Implementation of EPIRB receiver (#2754)

* Implementation of EPIRB receiver
* Baseband processing of EPIRB signal
* UI to ddecode and display EPIRB message with display on a map
* External application
* External proc element
* Delete CLAUDE.md

firmware/baseband/proc_epirb.cpp

@@ -0,0 +1,95 @@
+/*
+ * Copyright (C) 2024 EPIRB Receiver Implementation
+ *
+ * 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_epirb.hpp"
+
+#include "portapack_shared_memory.hpp"
+
+#include "dsp_fir_taps.hpp"
+
+#include "event_m4.hpp"
+#include <ch.h>
+
+EPIRBProcessor::EPIRBProcessor() {
+    // Configure the decimation filters for narrowband EPIRB signal
+    // Target: Reduce 2.457600 MHz to ~38.4 kHz for 400 bps processing
+    decim_0.configure(taps_11k0_decim_0.taps);
+    decim_1.configure(taps_11k0_decim_1.taps);
+    baseband_thread.start();
+}
+
+void EPIRBProcessor::execute(const buffer_c8_t& buffer) {
+    /* 2.4576MHz, 2048 samples */
+
+    // First decimation stage: 2.4576 MHz -> 307.2 kHz
+    const auto decim_0_out = decim_0.execute(buffer, dst_buffer);
+
+    // Second decimation stage: 307.2 kHz -> 38.4 kHz
+    const auto decim_1_out = decim_1.execute(decim_0_out, dst_buffer);
+    const auto decimator_out = decim_1_out;
+
+    /* 38.4kHz, 32 samples (approximately) */
+    feed_channel_stats(decimator_out);
+
+    // Process each decimated sample through the matched filter
+    for (size_t i = 0; i < decimator_out.count; i++) {
+        // Apply matched filter for BPSK demodulation
+        if (mf.execute_once(decimator_out.p[i])) {
+            // Feed symbol to clock recovery when matched filter triggers
+            clock_recovery(mf.get_output());
+        }
+    }
+}
+
+void EPIRBProcessor::consume_symbol(const float raw_symbol) {
+    // BPSK demodulation: positive = 1, negative = 0
+    const uint_fast8_t sliced_symbol = (raw_symbol >= 0.0f) ? 1 : 0;
+
+    // Decode bi-phase L encoding manually
+    // In bi-phase L: 0 = no transition, 1 = transition
+    // This is a simple edge detector
+    const auto decoded_symbol = sliced_symbol ^ last_symbol;
+    last_symbol = sliced_symbol;
+
+    // Build packet from decoded symbols
+    packet_builder.execute(decoded_symbol);
+}
+
+void EPIRBProcessor::payload_handler(const baseband::Packet& packet) {
+    // EPIRB packet received - validate and process
+    if (packet.size() >= 112) {  // Minimum EPIRB data payload size (112 bits)
+        packets_received++;
+        last_packet_timestamp = Timestamp::now();
+
+        // Create and send EPIRB packet message to application layer
+        const EPIRBPacketMessage message{packet};
+        shared_memory.application_queue.push(message);
+    }
+}
+
+void EPIRBProcessor::on_message(const Message* const message) {
+}
+
+int main() {
+    EventDispatcher event_dispatcher{std::make_unique<EPIRBProcessor>()};
+    event_dispatcher.run();
+    return 0;
+}