Function decodeBit

src/platforms/esp/32/drivers/rmt_rx/rmt_rx_channel.cpp.hpp:192–240

* @brief Decode single symbol to bit value * @param symbol RMT symbol to decode * @param timing Timing thresholds * @param ns_per_tick Cached nanoseconds per tick * @return 0 for bit 0, 1 for bit 1, -1 for invalid symbol * * Checks high time and low time against timing thresholds. * Returns -1 if timing doesn't match either bit pattern. */

 * Returns -1 if timing doesn't match either bit pattern.
 */
inline int decodeBit(RmtSymbol symbol, const ChipsetTiming4Phase &timing,
                     u32 ns_per_tick) {
    // Cast RmtSymbol to rmt_symbol_word_t to access bitfields
    const auto rmt_sym = fl::bit_cast<rmt_symbol_word_t>(symbol);

    // Convert tick durations to nanoseconds
    u32 high_ns = ticksToNs(rmt_sym.duration0, ns_per_tick);
    u32 low_ns = ticksToNs(rmt_sym.duration1, ns_per_tick);

    // WS2812B protocol: first duration is high, second is low
    // Check if levels match expected pattern (high=1, low=0)
    if (rmt_sym.level0 != 1 || rmt_sym.level1 != 0) {
        // Unexpected level pattern - possibly inverted signal or noise
        FL_WARN("decodeBit REJECTED: Invalid level pattern (level0=" << static_cast<int>(rmt_sym.level0)
               << ", level1=" << static_cast<int>(rmt_sym.level1) << ") - expected level0=1, level1=0");
        return -1;
    }

    // Decision logic: check if timing matches bit 0 pattern
    bool t0h_match =
        (high_ns >= timing.t0h_min_ns) && (high_ns <= timing.t0h_max_ns);
    bool t0l_match =
        (low_ns >= timing.t0l_min_ns) && (low_ns <= timing.t0l_max_ns);

    if (t0h_match && t0l_match) {
        return 0; // Bit 0
    }

    // Check if timing matches bit 1 pattern
    bool t1h_match =
        (high_ns >= timing.t1h_min_ns) && (high_ns <= timing.t1h_max_ns);
    bool t1l_match =
        (low_ns >= timing.t1l_min_ns) && (low_ns <= timing.t1l_max_ns);

    if (t1h_match && t1l_match) {
        return 1; // Bit 1
    }

    // Timing doesn't match either pattern - log detailed rejection reason
    FL_WARN("decodeBit REJECTED: Timing mismatch (high=" << high_ns << "ns, low=" << low_ns << "ns)");
    FL_WARN("  Bit0 thresholds: t0h=[" << timing.t0h_min_ns << "-" << timing.t0h_max_ns
           << "]ns (match=" << t0h_match << "), t0l=[" << timing.t0l_min_ns << "-" << timing.t0l_max_ns
           << "]ns (match=" << t0l_match << ")");
    FL_WARN("  Bit1 thresholds: t1h=[" << timing.t1h_min_ns << "-" << timing.t1h_max_ns
           << "]ns (match=" << t1h_match << "), t1l=[" << timing.t1l_min_ns << "-" << timing.t1l_max_ns
           << "]ns (match=" << t1l_match << ")");

    return -1; // Invalid
}

/**
 * @brief Decode RMT symbols to bytes (span-based implementation)