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Merge pull request #375 from grantsavill/bptc-fixes

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DMR: Improve BPTC(196,96), BPTC(128,77), and BPTC(16x2) FEC decoding
This commit is contained in:
lwvmobile
2026-11-14 20:16:00 -05:00
committed by GitHub
parent 33d6cdfb54 edf97e26b8
commit 138a48ad31
1 changed files with 145 additions and 44 deletions
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189
src/bptc.c
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@@ -213,8 +213,8 @@ uint32_t BPTC_196x96_Extract_Data(uint8_t InputDeInteleavedData[196],
}
}
/* ========== Pass 1: row Hamming(15,11) on rows 0..8 ========== */
for (i = 0; i < 9; i++)
/* ========== Pass 1: row Hamming(15,11) on rows 0..12 ========== */
for (i = 0; i < 13; i++)
{
for (j = 0; j < 15; j++)
{
@@ -232,8 +232,8 @@ uint32_t BPTC_196x96_Extract_Data(uint8_t InputDeInteleavedData[196],
fprintf(stderr, "%u", LineBefore[j] & 1);
fprintf(stderr, "\n");
#endif
/* Keep original data bits on failure */
for (j = 0; j < 11; j++)
/* Keep original bits on failure */
for (j = 0; j < 15; j++)
DataMatrix[i][j] = LineBefore[j];
}
else
@@ -253,8 +253,9 @@ uint32_t BPTC_196x96_Extract_Data(uint8_t InputDeInteleavedData[196],
#endif
}
}
for (j = 0; j < 11; j++)
DataMatrix[i][j] = LineCorrected[j];
/* Re-inject the full line (including corrected parity bits) in the matrix */
for (j = 0; j < 15; j++)
DataMatrix[i][j] = LineUncorrected[j];
}
}
#if BPTC_196x96_DEBUG
@@ -282,7 +283,7 @@ uint32_t BPTC_196x96_Extract_Data(uint8_t InputDeInteleavedData[196],
fprintf(stderr, "%u", ColumnBefore[j] & 1);
fprintf(stderr, "\n");
#endif
for (j = 0; j < 9; j++)
for (j = 0; j < 13; j++)
DataMatrix[j][i] = ColumnBefore[j];
}
else
@@ -301,8 +302,9 @@ uint32_t BPTC_196x96_Extract_Data(uint8_t InputDeInteleavedData[196],
#endif
}
}
for (j = 0; j < 9; j++)
DataMatrix[j][i] = ColumnCorrected[j];
/* Re-inject the full column (including corrected parity bits) in the matrix */
for (j = 0; j < 13; j++)
DataMatrix[j][i] = ColumnUncorrected[j];
}
}
#if BPTC_196x96_DEBUG
@@ -315,7 +317,7 @@ uint32_t BPTC_196x96_Extract_Data(uint8_t InputDeInteleavedData[196],
HammingIrrecoverableErrorNb = 0;
/* ========== Pass 2: rows ========== */
for (i = 0; i < 9; i++)
for (i = 0; i < 13; i++)
{
for (j = 0; j < 15; j++)
{
@@ -333,7 +335,7 @@ uint32_t BPTC_196x96_Extract_Data(uint8_t InputDeInteleavedData[196],
fprintf(stderr, "%u", LineBefore[j] & 1);
fprintf(stderr, "\n");
#endif
for (j = 0; j < 11; j++)
for (j = 0; j < 15; j++)
DataMatrix[i][j] = LineBefore[j];
}
else
@@ -352,8 +354,9 @@ uint32_t BPTC_196x96_Extract_Data(uint8_t InputDeInteleavedData[196],
#endif
}
}
for (j = 0; j < 11; j++)
DataMatrix[i][j] = LineCorrected[j];
/* Re-inject the full line (including corrected parity bits) in the matrix */
for (j = 0; j < 15; j++)
DataMatrix[i][j] = LineUncorrected[j];
}
}
#if BPTC_196x96_DEBUG
@@ -381,7 +384,7 @@ uint32_t BPTC_196x96_Extract_Data(uint8_t InputDeInteleavedData[196],
fprintf(stderr, "%u", ColumnBefore[j] & 1);
fprintf(stderr, "\n");
#endif
for (j = 0; j < 9; j++)
for (j = 0; j < 13; j++)
DataMatrix[j][i] = ColumnBefore[j];
}
else
@@ -400,8 +403,58 @@ uint32_t BPTC_196x96_Extract_Data(uint8_t InputDeInteleavedData[196],
#endif
}
}
for (j = 0; j < 9; j++)
DataMatrix[j][i] = ColumnCorrected[j];
/* Re-inject the full column (including corrected parity bits) in the matrix */
for (j = 0; j < 13; j++)
DataMatrix[j][i] = ColumnUncorrected[j];
}
}
/* Verify that all rows (0..12) and columns (0..14) have converged to zero syndrome.
* Hamming_15_11_decode never returns false because all 15 non-zero 4-bit syndromes
* map to a bit flip, so without a post-pass consistency check a noisy burst can
* mis-correct data bits in Pass 2 Columns while still reporting 0 errors. */
for (i = 0; i < 13; i++)
{
for (j = 0; j < 15; j++)
{
LineUncorrected[j] = DataMatrix[i][j];
}
if (Hamming_15_11_decode(LineUncorrected, LineCorrected, 1) == false)
{
HammingIrrecoverableErrorNb++;
}
else
{
for (j = 0; j < 15; j++)
{
if (LineUncorrected[j] != DataMatrix[i][j])
{
HammingIrrecoverableErrorNb++;
break;
}
}
}
}
for (i = 0; i < 15; i++)
{
for (j = 0; j < 13; j++)
{
ColumnUncorrected[j] = DataMatrix[j][i];
}
if (Hamming_13_9_decode(ColumnUncorrected, ColumnCorrected, 1) == false)
{
HammingIrrecoverableErrorNb++;
}
else
{
for (j = 0; j < 13; j++)
{
if (ColumnUncorrected[j] != DataMatrix[j][i])
{
HammingIrrecoverableErrorNb++;
break;
}
}
}
}
#if BPTC_196x96_DEBUG
@@ -430,12 +483,33 @@ uint32_t BPTC_196x96_Extract_Data(uint8_t InputDeInteleavedData[196],
DMRDataExtracted[k++] = DataMatrix[i][j];
}
uint32_t total_corr = row_corr_p1 + col_corr_p1 + row_corr_p2 + col_corr_p2;
uint32_t p2_corr = row_corr_p2 + col_corr_p2;
/* In DMR BPTC(196,96), R(0) and R(1) must be 0. Also reject R(2)==1 when the
* received R(2) bit was 0 or the matrix required heavy multi-pass corrections,
* because is_ras==1 bypasses downstream CRC checks when no RAS key is loaded. */
if (DataMatrix[0][2] != 0 || DataMatrix[0][1] != 0)
{
HammingIrrecoverableErrorNb++;
}
else if (DataMatrix[0][0] == 1 && ((InputDeInteleavedData[1] & 1) == 0 || total_corr > 8 || p2_corr > 2))
{
HammingIrrecoverableErrorNb++;
}
if (HammingIrrecoverableErrorNb == 0)
{
R[0] = DataMatrix[0][2]; /* R(0) */
R[1] = DataMatrix[0][1]; /* R(1) */
R[2] = DataMatrix[0][0]; /* R(2) */
}
else
{
R[0] = 0;
R[1] = 0;
R[2] = 0;
}
if (R[0] == 0 && R[1] == 0 && R[2] == 1)
*is_ras = 1;
@@ -466,7 +540,7 @@ uint32_t BPTC_128x77_Extract_Data(uint8_t InputDataMatrix[8][16], uint8_t DMRDat
uint32_t ParityCheckErrorNb = 0;
uint32_t NbOfOne;
uint8_t row_bad[7];
uint8_t row_bad[8];
uint8_t col_bad[16];
#if BPTC_128x77_DEBUG
@@ -479,9 +553,9 @@ uint32_t BPTC_128x77_Extract_Data(uint8_t InputDataMatrix[8][16], uint8_t DMRDat
DataMatrix[i][j] = (InputDataMatrix[i][j] & 1);
}
/* ---------- Pass 1: Hamming (16,11,4) on rows 0..6 ---------- */
/* ---------- Pass 1: Hamming (16,11,4) on rows 0..7 ---------- */
memset(row_bad, 0, sizeof(row_bad));
for (i = 0; i < 7; i++)
for (i = 0; i < 8; i++)
{
for (j = 0; j < 16; j++)
LineUncorrected[j] = DataMatrix[i][j];
@@ -496,13 +570,11 @@ uint32_t BPTC_128x77_Extract_Data(uint8_t InputDataMatrix[8][16], uint8_t DMRDat
fprintf(stderr, "%u", LineUncorrected[j] & 1);
fprintf(stderr, "\n");
#endif
for (j = 0; j < 11; j++)
DataMatrix[i][j] = LineUncorrected[j];
}
else
{
for (j = 0; j < 11; j++)
DataMatrix[i][j] = LineCorrected[j];
for (j = 0; j < 16; j++)
DataMatrix[i][j] = LineUncorrected[j];
}
}
#if BPTC_128x77_DEBUG
@@ -537,12 +609,14 @@ uint32_t BPTC_128x77_Extract_Data(uint8_t InputDataMatrix[8][16], uint8_t DMRDat
(unsigned)ParityCheckErrorNb);
#endif
/* ---------- Parity-guided single-bit repair ---------- */
/* ---------- Parity-guided bit repair ---------- */
{
uint32_t n_bad_rows = 0, n_bad_cols = 0;
uint32_t br = 0, bc = 0;
for (i = 0; i < 7; i++)
UNUSED(bc);
for (i = 0; i < 8; i++)
if (row_bad[i]) { n_bad_rows++; br = i; }
for (i = 0; i < 16; i++)
if (col_bad[i]) { n_bad_cols++; bc = i; }
@@ -558,29 +632,35 @@ uint32_t BPTC_128x77_Extract_Data(uint8_t InputDataMatrix[8][16], uint8_t DMRDat
fprintf(stderr, "\n");
#endif
if (n_bad_rows == 1 && n_bad_cols == 1 && bc < 11)
if (n_bad_rows == 1 && (n_bad_cols == 1 || n_bad_cols == 2))
{
DataMatrix[br][bc] ^= 1;
row_bad[br] = 0;
for (i = 0; i < 16; i++)
{
if (col_bad[i])
{
DataMatrix[br][i] ^= 1;
#if BPTC_128x77_DEBUG
fprintf(stderr,
" BPTC128 parity-guided FLIP at row=%u col=%u -> %u\n",
(unsigned)br, (unsigned)bc, (unsigned)DataMatrix[br][bc]);
fprintf(stderr,
" BPTC128 parity-guided FLIP at row=%u col=%u -> %u\n",
(unsigned)br, (unsigned)i, (unsigned)DataMatrix[br][i]);
#endif
}
}
row_bad[br] = 0;
}
#if BPTC_128x77_DEBUG
else if (n_bad_rows || n_bad_cols)
{
fprintf(stderr,
" BPTC128 no single-intersection flip "
"(need exactly 1 bad row and 1 data col)\n");
" BPTC128 no repair flip "
"(need 1 bad row and 1 or 2 bad cols)\n");
}
#endif
}
/* ---------- Pass 2: Hamming (16,11,4) again ---------- */
HammingIrrecoverableErrorNb = 0;
for (i = 0; i < 7; i++)
for (i = 0; i < 8; i++)
{
for (j = 0; j < 16; j++)
LineUncorrected[j] = DataMatrix[i][j];
@@ -594,13 +674,11 @@ uint32_t BPTC_128x77_Extract_Data(uint8_t InputDataMatrix[8][16], uint8_t DMRDat
fprintf(stderr, "%u", LineUncorrected[j] & 1);
fprintf(stderr, "\n");
#endif
for (j = 0; j < 11; j++)
DataMatrix[i][j] = LineUncorrected[j];
}
else
{
for (j = 0; j < 11; j++)
DataMatrix[i][j] = LineCorrected[j];
for (j = 0; j < 16; j++)
DataMatrix[i][j] = LineUncorrected[j];
}
}
#if BPTC_128x77_DEBUG
@@ -696,22 +774,45 @@ uint32_t BPTC_16x2_Extract_Data(uint8_t InputInterleavedData[32], uint8_t DMRDat
DMRDataExtracted[i] = DataMatrix[i] & 1;
}
/* Prepare the line to be corrected */
/* Prepare the first row (bits 0..15) to be corrected */
for(i = 0; i < 16; i++)
{
LineUncorrected[i] = DataMatrix[i] & 1;
}
/* Apply Hamming (16,11,4) code correction */
/* Apply Hamming (16,11,4) code correction to row 0 */
if(Hamming_16_11_4_decode(LineUncorrected, LineCorrected, 1) == false)
{
HammingIrrecoverableErrorNb++;
}
/* Copy the corrected content to the output buffer */
for(i = 0; i < 11; i++)
else
{
DMRDataExtracted[i] = LineCorrected[i] & 1;
/* Copy all 16 corrected bits (including parity bits 11..15) */
for(i = 0; i < 16; i++)
{
DMRDataExtracted[i] = LineUncorrected[i] & 1;
}
}
/* Prepare the second row (bits 16..31) to be corrected;
* 1^16 is a codeword of Hamming(16,11,4), so both even and odd parity rows are valid codewords */
for(i = 0; i < 16; i++)
{
LineUncorrected[i] = DataMatrix[i + 16] & 1;
}
/* Apply Hamming (16,11,4) code correction to row 1 */
if(Hamming_16_11_4_decode(LineUncorrected, LineCorrected, 1) == false)
{
HammingIrrecoverableErrorNb++;
}
else
{
/* Copy all 16 corrected bits (including parity bits 11..15) */
for(i = 0; i < 16; i++)
{
DMRDataExtracted[i + 16] = LineUncorrected[i] & 1;
}
}
/* Check Parity bits */