POCSAG: decoder fixes, serial output, TX polarity cleanup (#3130)

RX: fix address/batch-boundary handling, add numeric continuation, add heuristic type detection toggle, pass inverted polarity flag, stream decoded messages over USB serial. TX: rename phase to polarity (Standard/Inverted), fix function validation (&&→||), fix serial shell payload read (offset tracking, 31-byte cap, preserve msglen). Decoder: remove color escapes from output (plain text for all consumers), guard count_alpha_fill against empty string, keep numeric_len across continuation batches. Serial format: POCSAG <baud> <addr> <func> <pol> <type> "<msg>" hex:<hex> Quote escaping for embedded " and \\ in alpha messages.
2026-09-10 08:39:29 +00:00 · 2026-04-10 09:35:43 +03:00
parent fc18992442
commit dd006b4830
11 changed files with 549 additions and 92 deletions
@@ -1569,8 +1569,8 @@ class PocsagTosendMessage : public Message {
    constexpr PocsagTosendMessage(
        uint16_t baud = 1200,
        uint8_t type = 2,
-        char function = 'D',
-        char phase = 'N',
+        char function = 'A',
+        char polarity = 'S', /* 'S' = Standard (CCIR Rec. 584), 'I' = Inverted */
        uint8_t msglen = 0,
        uint8_t msg[31] = {0},
        uint64_t addr = 0)
@@ -1578,15 +1578,15 @@ class PocsagTosendMessage : public Message {
          baud{baud},
          type{type},
          function{function},
-          phase{phase},
+          polarity{polarity},
          msglen{msglen},
          addr{addr} {
        memcpy(this->msg, msg, 31);
    }
    uint16_t baud = 1200;
    uint8_t type = 2;
-    char function = 'D';
-    char phase = 'N';
+    char function = 'A';
+    char polarity = 'S'; /* 'S' = Standard, 'I' = Inverted */
    uint8_t msglen = 0;
    uint8_t msg[31] = {0};
    uint64_t addr = 0;
@@ -39,8 +39,6 @@ std::string bitrate_str(BitRate bitrate) {
            return "1200bps";
        case BitRate::FSK2400:
            return "2400bps";
-        case BitRate::FSK3200:
-            return "3200bps";
        default:
            return "????";
    }
@@ -352,30 +350,225 @@ int EccContainer::error_correct(uint32_t& val) {
    return errl;
 }

+// ----------------------------------------------------------------------------
+// Numeric character table: 4-bit BCD -> ASCII
+// ----------------------------------------------------------------------------
+static const char numeric_chars[16] = {
+    '0', '1', '2', '3', '4', '5', '6', '7',
+    '8', '9', 'R', 'U', ' ', '-', ']', '['};
+
+// Extract and bit-reverse a 4-bit nibble from a message codeword.
+// POCSAG numeric digits are transmitted LSB first, so bit 30 (first transmitted)
+// is the LSB of the digit value, not the MSB.
+static uint8_t decode_nibble(uint32_t codeword, int nibble_idx) {
+    int bit_pos = 30 - nibble_idx * 4;
+    // bit_pos is the first transmitted bit (LSB of digit)
+    // bit_pos-3 is the last transmitted bit (MSB of digit)
+    uint8_t n = 0;
+    n |= ((codeword >> (bit_pos - 3)) & 1) << 3;  // MSB of digit
+    n |= ((codeword >> (bit_pos - 2)) & 1) << 2;
+    n |= ((codeword >> (bit_pos - 1)) & 1) << 1;
+    n |= ((codeword >> (bit_pos - 0)) & 1) << 0;  // LSB of digit
+    return n;
+}
+
+// ----------------------------------------------------------------------------
+// Heuristic message type detection (first batch only)
+// ----------------------------------------------------------------------------
+
+// Count trailing fill characters in alpha buffer (NULL or space).
+static int count_alpha_fill(const std::string& data) {
+    if (data.empty()) return 0;
+    int fill = 0;
+    for (int i = data.size() - 1; i >= 0; --i) {
+        char c = data[i];
+        if (c == '\0' || c == ' ')
+            fill++;
+        else
+            break;
+    }
+    return fill;
+}
+
+// Count trailing fill nibbles (0xC = space) in numeric buffer.
+static int count_numeric_fill(const uint8_t* nibbles, int count) {
+    int fill = 0;
+    for (int i = count - 1; i >= 0; --i) {
+        if (nibbles[i] == 0x0C)
+            fill++;
+        else
+            break;
+    }
+    return fill;
+}
+
+// Score alpha interpretation: +3 alphanumeric/space, -2 other printable, -5 control.
+static int score_alpha(const std::string& data, int fill) {
+    int score = 0;
+    int content = 0;
+    int len = data.size();
+
+    for (int i = 0; i < len; ++i) {
+        unsigned char c = data[i];
+
+        // Skip trailing fill
+        if (i >= len - fill && (c == 0 || c == ' '))
+            continue;
+        if (c == 0)
+            continue;
+
+        content++;
+        if ((c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') ||
+            (c >= '0' && c <= '9') || c == ' ')
+            score += 3;
+        else if (c >= 0x20 && c <= 0x7E)
+            score -= 2;
+        else if (c == '\n' || c == '\r' || c == '\t' || c == 0x04)
+            score += 0;
+        else
+            score -= 5;
+    }
+
+    if (content > 0)
+        score += fill * fill * 3 + fill * 5;
+
+    return score;
+}
+
+// Score numeric interpretation on raw nibbles.
+static int score_numeric(const uint8_t* nibbles, int count, int fill) {
+    int raw_score = 0;
+    int scored = 0;
+    int digits = 0;
+    int u_count = 0;
+
+    // Pre-scan for U nibbles
+    for (int i = 0; i < count; ++i) {
+        if (nibbles[i] == 0x0C && i >= count - fill)
+            continue;
+        if (nibbles[i] == 0x0B)
+            u_count++;
+    }
+
+    bool urgent_prefix = (u_count == 1);
+
+    for (int i = 0; i < count; ++i) {
+        uint8_t n = nibbles[i];
+        if (n == 0x0C && i >= count - fill)
+            continue;
+
+        scored++;
+        if (n <= 0x09) {
+            raw_score += 3;
+            digits++;
+        } else if (n == 0x0B) {
+            raw_score += urgent_prefix ? -1 : -15;
+        } else if (n == 0x0A) {
+            raw_score -= 5;
+        } else {
+            raw_score -= 2;
+        }
+    }
+
+    int score = scored > 0 ? raw_score * 4 / 7 : 0;
+
+    // Phone numbers have at most ~15 digits
+    if (digits > 15)
+        score -= (digits - 15) * 5;
+
+    // Fill bonus (weaker than alpha: 1/16 vs 1/128 coincidence rate)
+    score += fill * fill;
+
+    return score;
+}
+
+DetectedType detect_message_type(const std::string& alpha,
+                                 const uint8_t* nibbles,
+                                 uint8_t nibble_count,
+                                 uint8_t msg_codewords) {
+    if (alpha.empty() && nibble_count == 0)
+        return DET_TONE;
+
+    // Long messages can't be numeric (phone numbers are short)
+    if (msg_codewords >= 8)
+        return DET_ALPHA;
+
+    int alpha_fill = count_alpha_fill(alpha);
+    int numeric_fill = count_numeric_fill(nibbles, nibble_count);
+
+    int sa = score_alpha(alpha, alpha_fill) + 2;  // Alpha prior bias
+    int sn = score_numeric(nibbles, nibble_count, numeric_fill);
+
+    // Short message boost for alpha (1-2 data codewords)
+    if (msg_codewords <= 3)
+        sa += 3;
+
+    return (sn > sa) ? DET_NUMERIC : DET_ALPHA;
+}
+
+// ----------------------------------------------------------------------------
+// Batch decoder
+// ----------------------------------------------------------------------------
+
 bool pocsag_decode_batch(const POCSAGPacket& batch, POCSAGState& state) {
    constexpr uint8_t codeword_max = 16;
    state.output.clear();

+    /* Only reset numeric accumulator when starting a new message,
+     * not on continuation batches — numeric_buf must be cumulative
+     * across multi-batch messages. */
+    const bool continuing_numeric =
+        (state.mode != STATE_HAVE_ADDRESS) &&
+        (state.out_type == MESSAGE) &&
+        state.type_decided &&
+        (state.detected == DET_NUMERIC);
+    if (!continuing_numeric)
+        state.numeric_len = 0;
+
+    /* Preserve new_message across batch boundary when STATE_HAVE_ADDRESS
+     * persists — the address was at the end of the previous batch and
+     * we haven't displayed it yet. Otherwise reset for this batch. */
+    if (state.mode != STATE_HAVE_ADDRESS)
+        state.new_message = false;
+
+    // Temporary nibble buffer for first-batch numeric decode.
+    uint8_t nibbles[max_batch_nibbles];
+    uint8_t nibble_count = 0;
+    uint8_t msg_codewords = 0;
+    // Also build raw alpha for heuristic (before non-printable replacement).
+    std::string raw_alpha{};
+
    while (state.codeword_index < codeword_max) {
        auto codeword = batch[state.codeword_index];
        bool is_address = (codeword & 0x80000000U) == 0;

-        // Error correct twice. First time to fix any errors it can,
-        // second time to count number of errors that couldn't be fixed.
-        state.ecc->error_correct(codeword);
+        // Single ECC call: fix errors and get error count.
        auto error_count = state.ecc->error_correct(codeword);

        switch (state.mode) {
            case STATE_CLEAR:
                if (is_address && codeword != POCSAG_IDLEWORD) {
                    state.function = (codeword >> 11) & 3;
-                    state.address = (codeword >> 10) & 0x1FFFF8U;  // 18 MSBs are transmitted
+                    state.address = (codeword >> 10) & 0x1FFFF8U;
+                    /* Frame number = lower 3 bits of RIC, derived from the
+                     * address codeword's position in the batch (not the
+                     * message codeword's position). codeword_index 0-15
+                     * maps to frames 0-7 via index >> 1. */
+                    state.address |= (state.codeword_index >> 1);
                    state.mode = STATE_HAVE_ADDRESS;
                    state.out_type = ADDRESS;
                    state.errors = error_count;
+                    state.new_message = true;
+                    state.type_decided = false;
+                    state.detected = DET_UNKNOWN;

                    state.ascii_idx = 0;
                    state.ascii_data = 0;
+                    state.prev_cw_err = 0;
+                    state.cur_cw_err = 0;
+                    nibble_count = 0;
+                    msg_codewords = 0;
+                    raw_alpha.clear();
                } else if (codeword == POCSAG_IDLEWORD) {
                    state.out_type = IDLE;
                }
@@ -383,54 +576,134 @@ bool pocsag_decode_batch(const POCSAGPacket& batch, POCSAGState& state) {

            case STATE_HAVE_ADDRESS:
                if (is_address) {
-                    // Got another address, return the current state.
+                    // Got another address. Run heuristic before returning if we have pending data.
+                    if (!state.type_decided && msg_codewords > 0) {
+                        state.detected = detect_message_type(raw_alpha, nibbles, nibble_count, msg_codewords);
+                        state.type_decided = true;
+                        state.msg_codewords = msg_codewords;
+                        if (state.detected == DET_NUMERIC) {
+                            state.numeric_len = 0;
+                            for (uint8_t ni = 0; ni < nibble_count && state.numeric_len < sizeof(state.numeric_buf); ++ni)
+                                state.numeric_buf[state.numeric_len++] = numeric_chars[nibbles[ni] & 0x0F];
+                        }
+                    }
                    state.mode = STATE_CLEAR;
                    return true;
                }

-                // First message codeword, complete the address.
-                state.address |= (state.codeword_index >> 1);  // Add in the 3 LSBs (frame #).
+                /* Frame number already applied in STATE_CLEAR.
+                 * Transition to message decoding. */
                state.mode = STATE_GETTING_MSG;
                [[fallthrough]];

            case STATE_GETTING_MSG:
                if (is_address) {
-                    // Codeword isn't a message, return the current state.
+                    // Message ended. Run heuristic before returning.
+                    if (!state.type_decided && msg_codewords > 0) {
+                        state.detected = detect_message_type(raw_alpha, nibbles, nibble_count, msg_codewords);
+                        state.type_decided = true;
+                        state.msg_codewords = msg_codewords;
+                        if (state.detected == DET_NUMERIC) {
+                            state.numeric_len = 0;
+                            for (uint8_t ni = 0; ni < nibble_count && state.numeric_len < sizeof(state.numeric_buf); ++ni)
+                                state.numeric_buf[state.numeric_len++] = numeric_chars[nibbles[ni] & 0x0F];
+                        }
+                    }
                    state.mode = STATE_CLEAR;
                    return true;
                }

                state.out_type = MESSAGE;
                state.errors += error_count;
-                state.ascii_data |= (codeword >> 11) & 0xFFFFF;  // Get 20 message bits.
+                msg_codewords++;
+
+                // Track per-codeword error level for character coloring.
+                // 0=clean, 1-2=corrected, 3=uncorrectable.
+                state.prev_cw_err = state.cur_cw_err;
+                state.cur_cw_err = (error_count >= 3) ? 3 : error_count;
+
+                // --- Alpha decode (always) ---
+                // Bits remaining from previous codeword inherit prev_cw_err.
+                // New 20 bits from this codeword use cur_cw_err.
+                // Characters spanning boundary get the worst of both.
+                uint32_t bits_from_prev = state.ascii_idx;  // leftover bits before adding new ones
+
+                state.ascii_data |= ((uint64_t)((codeword >> 11) & 0xFFFFF)) << (44 - state.ascii_idx);
                state.ascii_idx += 20;

-                // Raw 20 bits to 7 bit reversed ASCII.
-                // NB: This is processed MSB first, any remaining bits are shifted
-                // up so a whole 7 bits are processed with the next codeword.
                while (state.ascii_idx >= 7) {
+                    // Determine error level for this character.
+                    // If some bits came from previous codeword and some from current,
+                    // use the worst of both error levels.
+                    uint8_t char_err;
+                    if (bits_from_prev >= 7) {
+                        // Entire character from previous codeword's leftover bits.
+                        char_err = state.prev_cw_err;
+                        bits_from_prev -= 7;
+                    } else if (bits_from_prev > 0) {
+                        // Character spans boundary.
+                        char_err = std::max(state.prev_cw_err, state.cur_cw_err);
+                        bits_from_prev = 0;
+                    } else {
+                        // Entirely from current codeword.
+                        char_err = state.cur_cw_err;
+                    }
+
+                    // Extract top 7 bits from accumulator
+                    char ascii_char = (state.ascii_data >> 57) & 0x7F;
+                    state.ascii_data <<= 7;
                    state.ascii_idx -= 7;
-                    char ascii_char = (state.ascii_data >> state.ascii_idx) & 0x7F;

-                    // Reverse the bits. (TODO: __RBIT?)
-                    ascii_char = (ascii_char & 0xF0) >> 4 | (ascii_char & 0x0F) << 4;  // 01234567 -> 45670123
-                    ascii_char = (ascii_char & 0xCC) >> 2 | (ascii_char & 0x33) << 2;  // 45670123 -> 67452301
-                    ascii_char = (ascii_char & 0xAA) >> 2 | (ascii_char & 0x55);       // 67452301 -> 76543210
+                    // Reverse bits (LSB-first encoding)
+                    ascii_char = (ascii_char & 0xF0) >> 4 | (ascii_char & 0x0F) << 4;
+                    ascii_char = (ascii_char & 0xCC) >> 2 | (ascii_char & 0x33) << 2;
+                    ascii_char = (ascii_char & 0xAA) >> 2 | (ascii_char & 0x55);

-                    // Translate non-printable chars. TODO: Leave CRLF?
+                    // Store raw char for heuristic
+                    if (!state.type_decided)
+                        raw_alpha += ascii_char;
+
+                    // Translate non-printable chars.
                    if (ascii_char < 32 || ascii_char > 126)
                        state.output += ".";
                    else
                        state.output += ascii_char;
                }

-                state.ascii_data <<= 20;  // Remaining bits are for next iteration...
+                // --- Numeric decode ---
+                // First batch: accumulate nibbles locally for heuristic scoring.
+                // Continuation batches: if already decided numeric, decode directly
+                // into numeric_buf for the app layer.
+                if (!state.type_decided && nibble_count + 5 <= max_batch_nibbles) {
+                    for (int n = 0; n < 5; ++n) {
+                        nibbles[nibble_count++] = decode_nibble(codeword, n);
+                    }
+                } else if (state.type_decided && state.detected == DET_NUMERIC &&
+                           state.numeric_len + 5 <= (uint8_t)sizeof(state.numeric_buf)) {
+                    for (int n = 0; n < 5; ++n) {
+                        uint8_t nib = decode_nibble(codeword, n);
+                        state.numeric_buf[state.numeric_len++] = numeric_chars[nib & 0x0F];
+                    }
+                }
+
                break;
        }

        state.codeword_index++;
    }

+    // End of batch. If we have message data and type not yet decided, run heuristic.
+    if (state.out_type == MESSAGE && !state.type_decided && msg_codewords > 0) {
+        state.detected = detect_message_type(raw_alpha, nibbles, nibble_count, msg_codewords);
+        state.type_decided = true;
+        state.msg_codewords = msg_codewords;
+        if (state.detected == DET_NUMERIC) {
+            state.numeric_len = 0;
+            for (uint8_t ni = 0; ni < nibble_count && state.numeric_len < sizeof(state.numeric_buf); ++ni)
+                state.numeric_buf[state.numeric_len++] = numeric_chars[nibbles[ni] & 0x0F];
+        }
+    }
+
    return false;
 }

@@ -77,6 +77,17 @@ class EccContainer {
    uint32_t bch[1025];
 };

+/* Detected message type from heuristic scoring. */
+enum DetectedType : uint8_t {
+    DET_UNKNOWN,
+    DET_TONE,
+    DET_ALPHA,
+    DET_NUMERIC
+};
+
+/* Max numeric nibbles per batch: 16 codewords * 5 nibbles. */
+constexpr uint8_t max_batch_nibbles = 80;
+
 struct POCSAGState {
    EccContainer* ecc = nullptr;
    uint8_t codeword_index = 0;
@@ -84,17 +95,28 @@ struct POCSAGState {
    uint32_t address = 0;
    Mode mode = STATE_CLEAR;
    OutputType out_type = EMPTY;
-    uint32_t ascii_data = 0;
+    uint64_t ascii_data = 0;  // Was uint32_t — fixed overflow for long messages.
    uint32_t ascii_idx = 0;
    uint32_t errors = 0;
-    std::string output{};
+    uint8_t prev_cw_err = 0;    // Error level of previous codeword (for chars spanning boundary).
+    uint8_t cur_cw_err = 0;     // Error level of current codeword being decoded.
+    bool new_message = false;   // True when decoder starts a new address.
+    bool type_decided = false;  // True after first-batch heuristic runs.
+    DetectedType detected = DET_UNKNOWN;
+    uint8_t msg_codewords = 0;  // Message codewords in current batch (for heuristic).
+    std::string output{};       // Alpha decode (always populated, with color escapes).
+    // Numeric output is built into a separate local in pocsag_decode_batch
+    // and stored here only when heuristic detects numeric.
+    // Using a fixed buffer to avoid std::string overhead in external apps
+    // that embed POCSAGState (e.g. battleship).
+    char numeric_buf[80]{};
+    uint8_t numeric_len = 0;
 };

-const pocsag::BitRate pocsag_bitrates[4] = {
+const pocsag::BitRate pocsag_bitrates[3] = {
    pocsag::BitRate::FSK512,
    pocsag::BitRate::FSK1200,
    pocsag::BitRate::FSK2400,
-    pocsag::BitRate::FSK3200,
 };

 std::string bitrate_str(BitRate bitrate);
@@ -107,6 +129,10 @@ void pocsag_encode(const MessageType type, BCHCode& BCH_code, const uint32_t fun
 // Returns true if the batch has more to process.
 bool pocsag_decode_batch(const POCSAGPacket& batch, POCSAGState& state);

+// Heuristic: detect whether message content is numeric or alpha.
+// Called once after first batch of a new message.
+DetectedType detect_message_type(const std::string& alpha, const uint8_t* nibbles, uint8_t nibble_count, uint8_t msg_codewords);
+
 } /* namespace pocsag */

 #endif /*__POCSAG_H__*/
@@ -35,8 +35,7 @@ enum BitRate : uint32_t {
    UNKNOWN,
    FSK512 = 512,
    FSK1200 = 1200,
-    FSK2400 = 2400,
-    FSK3200 = 3200
+    FSK2400 = 2400
 };

 enum PacketFlag : uint32_t {
@@ -88,15 +87,25 @@ class POCSAGPacket {
        return flag_;
    }

+    void set_inverted(bool inverted) {
+        inverted_ = inverted;
+    }
+
+    bool inverted() const {
+        return inverted_;
+    }
+
    void clear() {
        codewords.fill(0);
        bitrate_ = 0u;
        flag_ = NORMAL;
+        inverted_ = false;
    }

   private:
    uint16_t bitrate_{0};
    PacketFlag flag_{NORMAL};
+    bool inverted_{false};
    batch_t codewords{};
    Timestamp timestamp_{};
 };