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DMR: Prevent false RAS detection and latching on non-RAS data bursts

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Check standard 24-bit Full LC and 16-bit CCITT CRCs before treating a flipped bptc_res_bits[2] bit as RAS, require PF/Reserved bits to be 0 for embedded LC RAS detection, and require two RAS bursts (or a key-verified RAS burst) to latch state->dmr_is_ras while clearing it on valid non-RAS BPTC bursts.
This commit is contained in:
Grant Savill
2026-11-15 00:18:03 +00:00
parent 33d6cdfb54
commit cd6ce80124
1 changed files with 63 additions and 15 deletions
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78
src/dmr_dburst.c
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@@ -60,6 +60,10 @@ void dmr_data_burst_handler(dsd_opts * opts, dsd_state * state, uint8_t info[196
uint8_t bptc_res_bits[3];
memset (bptc_res_bits, 0, sizeof(bptc_res_bits));
uint8_t crc_original_validity = 0;
static uint8_t ras_confirm_count = 0;
static uint8_t prev_dmr_is_ras = 0;
if (prev_dmr_is_ras == 1 && state->dmr_is_ras == 0)
ras_confirm_count = 0;
uint32_t crcmask = 0;
uint8_t crclen = 0;
@@ -305,13 +309,26 @@ void dmr_data_burst_handler(dsd_opts * opts, dsd_state * state, uint8_t info[196
{
if (is_ras)
{
CRCComputed = ras_mac_calculator(state, BPTCDmrDataByte, 9, 1);
if (CRCComputed == CRCExtracted)
uint8_t tmp_bytes[12];
uint32_t std_crc = 0;
memcpy (tmp_bytes, BPTCDmrDataByte, sizeof(tmp_bytes));
if (ComputeAndCorrectFullLinkControlCrc(tmp_bytes, &std_crc, crcmask) && std_crc == CRCExtracted)
{
memcpy (BPTCDmrDataByte, tmp_bytes, sizeof(tmp_bytes));
is_ras = 0;
CRCComputed = std_crc;
CRCCorrect = 1;
}
else
{
CRCComputed = ras_mac_calculator(state, BPTCDmrDataByte, 9, 1);
if (CRCComputed == CRCExtracted)
CRCCorrect = 1;
#ifdef DEBUG_RAS
fprintf (stderr, " EXT: %06X; MAC: %06X;", CRCExtracted, CRCComputed);
#endif
#ifdef DEBUG_RAS
fprintf (stderr, " EXT: %06X; MAC: %06X;", CRCExtracted, CRCComputed);
#endif
}
}
else CRCCorrect = ComputeAndCorrectFullLinkControlCrc(BPTCDmrDataByte, &CRCComputed, crcmask);
@@ -354,18 +371,28 @@ void dmr_data_burst_handler(dsd_opts * opts, dsd_state * state, uint8_t info[196
//run CCITT on other data forms
else
{
if (is_ras == 1)
uint32_t std_crc = ComputeCrcCCITT(BPTCDmrDataBit);
if (std_crc == CRCExtracted)
{
is_ras = 0;
CRCComputed = std_crc;
CRCCorrect = 1;
}
else if (is_ras == 1)
{
CRCComputed = ras_mac_calculator(state, BPTCDmrDataByte, 10, 0);
if (CRCComputed == CRCExtracted) CRCCorrect = 1;
else CRCCorrect = 0;
#ifdef DEBUG_RAS
fprintf (stderr, " EXT: %04X; MAC: %04X;", CRCExtracted, CRCComputed);
#endif
}
else CRCComputed = ComputeCrcCCITT(BPTCDmrDataBit);
if (CRCComputed == CRCExtracted) CRCCorrect = 1;
else CRCCorrect = 0;
else
{
CRCComputed = std_crc;
CRCCorrect = 0;
}
}
//if this is a RAS system, set the CRC to okay if irrecoverable errors are okay
@@ -473,9 +500,11 @@ void dmr_data_burst_handler(dsd_opts * opts, dsd_state * state, uint8_t info[196
/* Compute the 5 bit CRC */
CRCComputed = ComputeCrc5Bit(LC_DataBit);
//read ahead first two bytes, look for 1X10 or 2X10 pattern
//read ahead first two bytes, look for 1X10 or 2X10 pattern (with PF/R bits 0)
uint16_t ras_test = (uint16_t)(ConvertBitIntoBytes(&LC_DataBit[0], 16) & 0x30FF);
if ((IrrecoverableErrors == 0) && (ras_test == 0x2010 || ras_test == 0x1010))
if ((IrrecoverableErrors == 0) &&
(LC_DataBit[0] == 0) && (LC_DataBit[1] == 0) &&
(ras_test == 0x2010 || ras_test == 0x1010))
{
is_ras = 1;
if (state->ras_effective_key != 0)
@@ -702,9 +731,28 @@ void dmr_data_burst_handler(dsd_opts * opts, dsd_state * state, uint8_t info[196
fprintf (stderr, "%s", KNRM);
}
//might flicker the terminal on partially enabled systems, may need to find a better placement
if (IrrecoverableErrors == 0 && (is_bptc || is_emb) && databurst != 0x05 && databurst != 0x07 && databurst != 0x09)
state->dmr_is_ras = is_ras;
//require a key-verified RAS burst or 2 RAS bursts to latch [RAS]; clear on valid non-PI non-RAS BPTC burst
if (IrrecoverableErrors == 0 && is_ras == 1 && (is_bptc || is_emb) && databurst != 0x05 && databurst != 0x07 && databurst != 0x09)
{
if (state->ras_effective_key != 0 && CRCCorrect == 1)
{
ras_confirm_count = 2;
state->dmr_is_ras = 1;
}
else if ((is_bptc || is_emb) && databurst != 0x00)
{
if (ras_confirm_count < 2)
ras_confirm_count++;
if (ras_confirm_count >= 2)
state->dmr_is_ras = 1;
}
}
else if (IrrecoverableErrors == 0 && is_ras == 0 && is_bptc && CRCCorrect == 1 && databurst != 0x00 && databurst != 0x05 && databurst != 0x07 && databurst != 0x09)
{
ras_confirm_count = 0;
state->dmr_is_ras = 0;
}
prev_dmr_is_ras = state->dmr_is_ras;
if (IrrecoverableErrors == 0 && CRCCorrect == 0 && is_ras == 0 && databurst != 0x09 && databurst != 0x05)
{