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M17 - PKT CRC Immediately Following Terminator Byte and Fixes;

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lwvmobile
2024-03-17 19:28:53 -04:00
parent 3a44affc63
commit df28ebe573
1 changed files with 21 additions and 6 deletions
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27
src/m17.c
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@@ -2724,7 +2724,17 @@ void encodeM17PKT(dsd_opts * opts, dsd_state * state)
if (m17_p1_packed[x] == 0) break; //stop at the termination byte
x++;
}
crc_cmp = crc16m17(m17_p1_packed, x+1); //+1 on len to make it match Woj's calculated value of 0x2F6F on the default sample
//NOTE to self: Revert changes in this commit, if issues with CRC on PKT, or
//the CRC really does go on the last 16 bits of the payload
//debug dump the packed payload up to x, or x+1
// fprintf (stderr, "\n P1P:");
// for (i = 0; i < x+1; i++)
// fprintf (stderr, "%02X", m17_p1_packed[i]);
// fprintf (stderr, "\n");
crc_cmp = crc16m17(m17_p1_packed, x+1); //either x, or x+1?
//debug dump CRC (when pad is literally zero)
fprintf (stderr, " X: %d; LAST: %02X; TERM: %02X; CRC: %04X", x, m17_p1_packed[x-1], m17_p1_packed[x], crc_cmp);
@@ -2732,7 +2742,9 @@ void encodeM17PKT(dsd_opts * opts, dsd_state * state)
ptr = (block*25*8) - 16;
//attach the crc16 bits to the end of the PKT data
for (i = 0; i < 16; i++) m17_p1_full[ptr+i] = (crc_cmp >> 15-i) & 1;
// for (i = 0; i < 16; i++) m17_p1_full[ptr+i] = (crc_cmp >> 15-i) & 1; //this one puts it as the last 16-bits of the full payload
for (i = 0; i < 16; i++) m17_p1_full[k++] = (crc_cmp >> 15-i) & 1; //this one puts it immediately after the terminating byte
//debug the full payload
fprintf (stderr, "\n M17 Packet FULL: ");
@@ -3016,13 +3028,16 @@ void processM17PKT(dsd_opts * opts, dsd_state * state)
if (eot)
{
//do a CRC check
uint16_t crc_cmp = crc16m17(state->m17_pkt, total+1); //+1 on len to make it match Woj's calculated value of 0x2F6F on the default sample
uint16_t crc_ext = (state->m17_pkt[end-2] << 8) + state->m17_pkt[end-1];
uint16_t crc_cmp = crc16m17(state->m17_pkt, total+1); //total, or total+1?
// uint16_t crc_ext = (state->m17_pkt[end-2] << 8) + state->m17_pkt[end-1]; //extract from last 16-bits of the payload, or
uint16_t crc_ext = (state->m17_pkt[total+1] << 8) + state->m17_pkt[total+2]; //immediately after the terminating byte
if (crc_cmp == crc_ext)
decodeM17PKT(opts, state, state->m17_pkt, end-2);
// decodeM17PKT(opts, state, state->m17_pkt, end-2);
decodeM17PKT(opts, state, state->m17_pkt, total); //end-2 if CRC at the end, total if CRC after term
else if (opts->aggressive_framesync == 0) //CRC Bypass, check anyways (if enabled)
decodeM17PKT(opts, state, state->m17_pkt, end-2); //end-2, or do full contents? 25*31-2
// decodeM17PKT(opts, state, state->m17_pkt, end-2);
decodeM17PKT(opts, state, state->m17_pkt, total); //end-2 if CRC at the end, total if CRC after term
if (crc_cmp != crc_ext)
fprintf (stderr, " (CRC ERR) ");