Method decodeLoop

src/core/RttyDecoder.cpp:159–305

// ── Decode loop (worker thread) ───────────────────────────────────────────────

void RttyDecoder::decodeLoop()
{
    constexpr int kChunkSamples = 240;  // 10 ms at 24 kHz
    constexpr int kChunkBytes   = kChunkSamples * static_cast<int>(sizeof(float));

    // Envelope time constant: 0.3/baud gives crossover in ~0.2 bit periods,
    // fast enough for start-bit detection while still smoothing carrier ripple.
    auto calcEnvAlpha = [](double baud) {
        return 1.0 - std::exp(-baud / (kSampleRate * 0.3));
    };

    // Schmitt trigger hysteresis: a 10% band prevents chattering at the
    // mark/space boundary when the signal is near equal amplitude.
    constexpr double kHyst = 0.10;

    double baud        = m_baudRate.load();
    double envAlpha    = calcEnvAlpha(baud);
    int    statsTick   = 0;

    // Decoder state machine
    int    prevBit     = 1;  // idle = mark
    int    curBit      = 1;
    bool   inChar      = false;
    int    bitCount    = 0;
    int    shiftReg    = 0;
    bool   figsMode    = false;
    double bitClock    = 0.0;
    double samplesPerBit = kSampleRate / baud;

    while (m_running) {
        if (m_paramsChanged.exchange(false)) {
            recalcFilterCoeffs();
            baud          = m_baudRate.load();
            envAlpha      = calcEnvAlpha(baud);
            samplesPerBit = kSampleRate / baud;
            // Reset bit-level state but preserve figsMode: the LTRS/FIGS
            // shift is session state set by received codes, not a filter
            // parameter, so a baud/mark change mid-stream shouldn't flip
            // the character set back to LTRS unexpectedly.
            inChar   = false;
            bitCount = 0;
            shiftReg = 0;
            prevBit  = 1;
            curBit   = 1;
            bitClock = 0.0;
        }

        QByteArray chunk;
        {
            QMutexLocker lock(&m_bufMutex);
            if (m_ringBuf.size() < kChunkBytes) {
                lock.unlock();
                QThread::msleep(10);
                continue;
            }
            chunk = m_ringBuf.left(kChunkBytes);
            m_ringBuf.remove(0, kChunkBytes);
        }