@@ -35,29 +35,42 @@
#include "libavformat/avformat.h"
#include "libavformat/demux.h"
+#define MAX_BURST 5 // Tradeoff between undetected errors and correction capacity values from 2 to 5 are reasonable
+
+static int burst_len(unsigned u)
+{
+ if (!u)
+ return 0;
+
+ while(!(u&1))
+ u>>=1;
+ return 1+av_log2(u);
+}
+
/**
* Check and correct RDS block
* @param[out] group the data bits are returned here
* @param block block nu,ber (0 to 3)
* @return 1 if correctable single bit error, 0 if no error, >99 if non correctable errors
*/
-static int check_rds_block(uint16_t group[4], const float diff[104], int block)
+static int check_rds_block(Station *station, uint16_t group[4], const float diff[104], const int block)
{
#define RDS_G 0x5B9 //101 1011 1001
static const uint16_t offset[4] = {0x0FC, 0x198, 0x168, 0x1B4};
unsigned codeword = 0;
- unsigned syndrom = 0;
- //we carry floats through to here so we can do a soft decission decoder
- //ATM lets just do hard decission decoding that should be more than good enough
+ unsigned syndrom = 0;
+ const float *blockdiff = diff + block*26;
//FIXME we could do this more efficiently but does it matter?
for(int i=0; i<26; i++) {
- int bit = (diff[i + block*26]<0);
+ int bit = blockdiff[i] < 0;
+
codeword += codeword + bit;
syndrom += syndrom + bit;
if (syndrom & (1<<10))
syndrom ^= RDS_G;
}
+
if (block==2 && (group[1]&0x800)) {
syndrom ^= 0x350;
}else
@@ -66,25 +79,24 @@ static int check_rds_block(uint16_t group[4], const float diff[104], int block)
group[block] = codeword >> 10;
- // try correcting some basic errors
- if (syndrom) {
- for (unsigned e = 1; e <= 2; e ++) {
- unsigned mask = 255 >> (8-e);
- unsigned syndrom1 = mask;
- for(int i=0; i<27-e; i++) {
- if (syndrom == syndrom1) {
- group[block] ^= (mask<<i) >> 10;
- return e;
+ // try correcting the most common error patterns
+ for (int i=0; i<27-MAX_BURST; i++) {
+ if (!(syndrom>>MAX_BURST)) {
+ int ret = burst_len(syndrom);
+ group[block] ^= (syndrom << i) >> 10;
+
+ return ret;
}
- syndrom1 += syndrom1;
- if (syndrom1 & (1<<10))
- syndrom1 ^= RDS_G;
}
+
+ return ret;
}
- return 100; // this is a good place do a 2nd pass with a soft decssion multi bit decoder
+ if (syndrom&1)
+ syndrom ^= RDS_G;
+ syndrom >>= 1;
}
- return 0;
+ return 20;
}
static int decode_rds_group(SDRContext *sdr, SDRStream *sst, uint16_t group[4])
@@ -131,6 +143,7 @@ int ff_sdr_decode_rds(SDRContext *sdr, SDRStream *sst, AVComplexFloat *signal)
uint16_t group[4];
int64_t num_step_in_p2 = sdr->sdr_sample_rate * (int64_t)sst->block_size_p2;
int64_t den_step_on_p2 = sdr->block_size * 2375LL;
+ Station *station = sst->station;
#define IDX(I) ((I)*num_step_in_p2/den_step_on_p2)
av_assert0(sst->rds_ring_pos <= sst->rds_ring_size - 2*sst->block_size_p2);
@@ -171,7 +184,7 @@ int ff_sdr_decode_rds(SDRContext *sdr, SDRStream *sst, AVComplexFloat *signal)
for (phase = 0; phase < 104; phase++) {
int error = 0;
for (int block = 0; block < 4; block++) {
- error += check_rds_block(group, diff + phase, block);
+ error += check_rds_block(station, group, diff + phase, block);
}
if (error < best_errors) {
best_errors = error;
@@ -184,7 +197,7 @@ int ff_sdr_decode_rds(SDRContext *sdr, SDRStream *sst, AVComplexFloat *signal)
if (best_errors < 10) {
int error = 0;
for (int block = 0; block < 4; block++) {
- error += check_rds_block(group, diff + best_phase, block);
+ error += check_rds_block(station, group, diff + best_phase, block);
}
//have to recheck because of floats
if (error < 10) {
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc> --- libavradio/rds.c | 55 ++++++++++++++++++++++++++++++------------------ 1 file changed, 34 insertions(+), 21 deletions(-)