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POCSAG: show '?' for characters from uncorrectable codewords (#3138)

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Use per-character error tracking to substitute '?' when a
character's bits came from an uncorrectable codeword (BCH error_count >= 3). 
Previously these displayed as garbage.
This commit is contained in:
VasylSamoilov
2026-04-18 19:56:33 +03:00
committed by GitHub
parent c095a88cb3
commit 396f8aef41
2 changed files with 22 additions and 10 deletions
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firmware/common/pocsag.cpp
+19 -8
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@@ -537,6 +537,9 @@ bool pocsag_decode_batch(const POCSAGPacket& batch, POCSAGState& state) {
uint8_t msg_codewords = 0;
// Also build raw alpha for heuristic (before non-printable replacement).
std::string raw_alpha{};
// Track whether any characters came from uncorrectable codewords.
// If so, heuristic scoring is unreliable — skip it and default to alpha.
bool has_bad_chars = false;
while (state.codeword_index < codeword_max) {
auto codeword = batch[state.codeword_index];
@@ -578,7 +581,9 @@ bool pocsag_decode_batch(const POCSAGPacket& batch, POCSAGState& state) {
if (is_address) {
// 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.detected = has_bad_chars
? DET_ALPHA
: detect_message_type(raw_alpha, nibbles, nibble_count, msg_codewords);
state.type_decided = true;
state.msg_codewords = msg_codewords;
if (state.detected == DET_NUMERIC) {
@@ -600,7 +605,9 @@ bool pocsag_decode_batch(const POCSAGPacket& batch, POCSAGState& state) {
if (is_address) {
// 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.detected = has_bad_chars
? DET_ALPHA
: detect_message_type(raw_alpha, nibbles, nibble_count, msg_codewords);
state.type_decided = true;
state.msg_codewords = msg_codewords;
if (state.detected == DET_NUMERIC) {
@@ -632,9 +639,8 @@ bool pocsag_decode_batch(const POCSAGPacket& batch, POCSAGState& state) {
state.ascii_idx += 20;
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.
// Per-character error level from codeword error tracking.
// Characters spanning a codeword boundary get the worst level.
uint8_t char_err;
if (bits_from_prev >= 7) {
// Entire character from previous codeword's leftover bits.
@@ -663,8 +669,11 @@ bool pocsag_decode_batch(const POCSAGPacket& batch, POCSAGState& state) {
if (!state.type_decided)
raw_alpha += ascii_char;
// Translate non-printable chars.
if (ascii_char < 32 || ascii_char > 126)
// Substitute '?' for characters from uncorrectable codewords
if (char_err >= 3) {
state.output += "?";
has_bad_chars = true;
} else if (ascii_char < 32 || ascii_char > 126)
state.output += ".";
else
state.output += ascii_char;
@@ -694,7 +703,9 @@ bool pocsag_decode_batch(const POCSAGPacket& batch, POCSAGState& state) {
// 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.detected = has_bad_chars
? DET_ALPHA
: detect_message_type(raw_alpha, nibbles, nibble_count, msg_codewords);
state.type_decided = true;
state.msg_codewords = msg_codewords;
if (state.detected == DET_NUMERIC) {