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Added RDS error correction (still needs better clock recovery)

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AlexandreRouma 2022-07-08 01:02:36 +02:00
parent bdd4998b1b
commit 96f5b37f76
2 changed files with 53 additions and 39 deletions
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89
decoder_modules/radio/src/rds.cpp
View File

@ -53,8 +53,10 @@ namespace rds {
const int BLOCK_LEN = 26;
const int DATA_LEN = 16;
const int POLY_LEN = 10;
const uint16_t LFSR_POLY = 0x5B9;
const uint16_t IN_POLY = 0x31B;
// 9876543210
const uint16_t LFSR_POLY = 0b0110111001;
const uint16_t IN_POLY = 0b1100011011;
void RDSDecoder::process(uint8_t* symbols, int count) {
for (int i = 0; i < count; i++) {
@ -71,10 +73,6 @@ namespace rds {
auto synIt = SYNDROMES.find(syn);
bool knownSyndrome = synIt != SYNDROMES.end();
sync = std::clamp<int>(knownSyndrome ? ++sync : --sync, 0, 4);
// if (knownSyndrome) {
// printf("Found known syn: %04X\n", syn);
// }
// If we're still no longer in sync, try to resync
if (!sync) { continue; }
@ -89,9 +87,7 @@ namespace rds {
}
// Save block while correcting errors (NOT YET)
blocks[type] = shiftReg;//correctErrors(shiftReg, type);
//printf("Block type: %d, Sync: %d, KnownSyndrome: %s, contGroup: %d, offset: %d\n", type, sync, knownSyndrome ? "yes" : "no", contGroup, i);
blocks[type] = correctErrors(shiftReg, type, blockAvail[type]);
// Update continous group count
if (type == BLOCK_TYPE_A) { contGroup = 1; }
@ -121,14 +117,14 @@ namespace rds {
return syn;
}
uint32_t RDSDecoder::correctErrors(uint32_t block, BlockType type) {
uint32_t RDSDecoder::correctErrors(uint32_t block, BlockType type, bool& recovered) {
// Subtract the offset from block
block ^= (uint32_t)OFFSETS[type];
// Init the syndrome and output
uint16_t syn = 0;
uint32_t out = block;
// Subtract the offset from block
block ^= (uint32_t)OFFSETS[type];
// Feed in the data
for (int i = BLOCK_LEN - 1; i >= 0; i--) {
// Shift the syndrome and keep the output
@ -142,27 +138,33 @@ namespace rds {
syn ^= IN_POLY * ((block >> i) & 1);
}
// Use the syndrome register to do error correction
// TODO: For some reason there's always zeros in the syn when starting
uint16_t firstSyn = syn;
// Use the syndrome register to do error correction if errors are present
uint8_t errorFound = 0;
for (int i = DATA_LEN - 1; i >= 0; i--) {
// Check if the 5 leftmost bits are all zero
errorFound |= !(syn & 0b11111);
if (syn) {
for (int i = DATA_LEN - 1; i >= 0; i--) {
// Check if the 5 leftmost bits are all zero
errorFound |= !(syn & 0b11111);
// Write output
uint8_t outBit = (syn >> (POLY_LEN - 1)) & 1;
out ^= (errorFound & outBit) << (i + POLY_LEN);
// Write output
uint8_t outBit = (syn >> (POLY_LEN - 1)) & 1;
out ^= (errorFound & outBit) << (i + POLY_LEN);
// Shift syndrome
syn = (syn << 1) & 0b1111111111;
syn ^= LFSR_POLY * outBit * !errorFound;
// Shift syndrome
syn = (syn << 1) & 0b1111111111;
syn ^= LFSR_POLY * outBit * !errorFound;
}
}
recovered = !(syn & 0b11111);
// TODO: mark block as irrecoverable if too damaged
if (errorFound) {
printf("Error found\n");
}
// // One last check
// if (errorFound) {
// printf("Error found: %04X -> %04X, %08X -> %08X\n", firstSyn, syn, block, out);
// }
// else if (!recovered) {
// printf("Non recoverable error\n");
// }
return out;
}
@ -172,6 +174,9 @@ namespace rds {
auto now = std::chrono::high_resolution_clock::now();
anyGroupLastUpdate = now;
// Make sure blocks A and B are available
if (!blockAvail[BLOCK_TYPE_A] || !blockAvail[BLOCK_TYPE_B]) { return; }
// Decode PI code
countryCode = (blocks[BLOCK_TYPE_A] >> 22) & 0xF;
programCoverage = (AreaCoverage)((blocks[BLOCK_TYPE_A] >> 18) & 0xF);
@ -194,7 +199,7 @@ namespace rds {
uint8_t diOffset = 3 - offset;
uint8_t psOffset = offset * 2;
if (groupVer == GROUP_VER_A) {
if (groupVer == GROUP_VER_A && blockAvail[BLOCK_TYPE_C]) {
alternateFrequency = (blocks[BLOCK_TYPE_C] >> 10) & 0xFFFF;
}
@ -203,8 +208,10 @@ namespace rds {
decoderIdent |= (diBit << diOffset);
// Write chars at offset the PSName
programServiceName[psOffset] = (blocks[BLOCK_TYPE_D] >> 18) & 0xFF;
programServiceName[psOffset + 1] = (blocks[BLOCK_TYPE_D] >> 10) & 0xFF;
if (blockAvail[BLOCK_TYPE_D]) {
programServiceName[psOffset] = (blocks[BLOCK_TYPE_D] >> 18) & 0xFF;
programServiceName[psOffset + 1] = (blocks[BLOCK_TYPE_D] >> 10) & 0xFF;
}
}
else if (groupType == 2) {
group2LastUpdate = now;
@ -221,15 +228,21 @@ namespace rds {
// Write char at offset in Radiotext
if (groupVer == GROUP_VER_A) {
uint8_t rtOffset = offset * 4;
radioText[rtOffset] = (blocks[BLOCK_TYPE_C] >> 18) & 0xFF;
radioText[rtOffset + 1] = (blocks[BLOCK_TYPE_C] >> 10) & 0xFF;
radioText[rtOffset + 2] = (blocks[BLOCK_TYPE_D] >> 18) & 0xFF;
radioText[rtOffset + 3] = (blocks[BLOCK_TYPE_D] >> 10) & 0xFF;
if (blockAvail[BLOCK_TYPE_C]) {
radioText[rtOffset] = (blocks[BLOCK_TYPE_C] >> 18) & 0xFF;
radioText[rtOffset + 1] = (blocks[BLOCK_TYPE_C] >> 10) & 0xFF;
}
if (blockAvail[BLOCK_TYPE_D]) {
radioText[rtOffset + 2] = (blocks[BLOCK_TYPE_D] >> 18) & 0xFF;
radioText[rtOffset + 3] = (blocks[BLOCK_TYPE_D] >> 10) & 0xFF;
}
}
else {
uint8_t rtOffset = offset * 2;
radioText[rtOffset] = (blocks[BLOCK_TYPE_D] >> 18) & 0xFF;
radioText[rtOffset + 1] = (blocks[BLOCK_TYPE_D] >> 10) & 0xFF;
if (blockAvail[BLOCK_TYPE_D]) {
radioText[rtOffset] = (blocks[BLOCK_TYPE_D] >> 18) & 0xFF;
radioText[rtOffset + 1] = (blocks[BLOCK_TYPE_D] >> 10) & 0xFF;
}
}
}
}

3
decoder_modules/radio/src/rds.h
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@ -138,7 +138,7 @@ namespace rds {
private:
static uint16_t calcSyndrome(uint32_t block);
static uint32_t correctErrors(uint32_t block, BlockType type);
static uint32_t correctErrors(uint32_t block, BlockType type, bool& recovered);
void decodeGroup();
bool anyGroupValid();
@ -152,6 +152,7 @@ namespace rds {
BlockType lastType = BLOCK_TYPE_A;
int contGroup = 0;
uint32_t blocks[_BLOCK_TYPE_COUNT];
bool blockAvail[_BLOCK_TYPE_COUNT];
// All groups
std::mutex groupMtx;