static int write_header(avro_file_writer_t w)
{
int rval;
uint8_t version = 1;
/* TODO: remove this static buffer */
avro_writer_t schema_writer;
char schema_buf[64 * 1024];
const avro_encoding_t *enc = &avro_binary_encoding;
/* Generate random sync */
generate_sync(w);
check(rval, avro_write(w->writer, "Obj", 3));
check(rval, avro_write(w->writer, &version, 1));
check(rval, enc->write_long(w->writer, 3));
check(rval, enc->write_string(w->writer, "avro.sync"));
check(rval, enc->write_bytes(w->writer, w->sync, sizeof(w->sync)));
check(rval, enc->write_string(w->writer, "avro.codec"));
check(rval, enc->write_bytes(w->writer, "null", 4));
check(rval, enc->write_string(w->writer, "avro.schema"));
schema_writer = avro_writer_memory(schema_buf, sizeof(schema_buf));
rval = avro_schema_to_json(w->writers_schema, schema_writer);
if (rval) {
avro_writer_free(schema_writer);
return rval;
}
check(rval,
enc->write_bytes(w->writer, schema_buf,
avro_writer_tell(schema_writer)));
check(rval, enc->write_long(w->writer, 0));
return write_sync(w);
}
int main(int argc,char *argv[]){
unsigned char data[FRAMEBITS/8]; // One minor frame
unsigned char symbols[2*FRAMEBITS];
unsigned char nsymbols[2*FRAMEBITS];
int i,fd;
char *filename;
struct stat statbuf;
off_t length;
short *samples;
int nsamples;
int start;
int startsync = SYNC_FAIL,endsync = SYNC_FAIL;
void *vd; // Viterbi decoder handle
int symerrors;
int firstsample;
int frame;
int begin;
int maxmetric,minmetric;
int ind;
char *locale;
double clock_tolerance = 5; // Maximum allowable clock offset, samples/frame
if((locale = getenv("LANG")) != NULL)
setlocale(LC_ALL,locale);
else
setlocale(LC_ALL,"en_US.utf8");
begin = 0;
while((i = getopt(argc,argv,"c:o:r:t:")) != EOF){
switch(i){
case 't':
clock_tolerance = atof(optarg);
break;
case 'c':
Symrate = atof(optarg);
break;
case 'r':
Samprate = atof(optarg);
break;
case 'o':
begin = atoi(optarg); // Starting sample, default 0
break;
}
}
Symbolsamples = Samprate/Symrate;
Framesamples = Symbolsamples * 2*FRAMEBITS;
// Read baseband samples, downsampled to Samprate (important!) and look for sync vector
filename = argv[optind];
if(lstat(filename,&statbuf) == -1){
fprintf(stderr,"lstat(%s) failed: %s\n",filename,strerror(errno));
exit(1);
}
if(!S_ISREG(statbuf.st_mode)){
fprintf(stderr,"%s is not an ordinary file\n",filename);
exit(1);
}
length = statbuf.st_size;
if((fd = open(filename,O_RDONLY)) == -1){
fprintf(stderr,"open(%s,readonly) failed; %s\n",filename,strerror(errno));
exit(1);
}
if((samples = mmap(NULL,length,PROT_READ,MAP_SHARED,fd,0)) == MAP_FAILED){
fprintf(stderr,"mmap(%s,%lld) failed: %s\n",filename,
(long long)length,strerror(errno));
close(fd);
exit(1);
}
nsamples = length / sizeof(*samples);
printf("%s: %'d samples, %'.3lf seconds @ %.1lf Hz\n",filename,
nsamples,nsamples/Samprate,Samprate);
generate_sync(Symrate);
vd = create_viterbi224(FRAMEBITS);
if(vd == NULL){
fprintf(stderr,"Can't create viterbi decoder\n");
exit(2);
}
for(frame=1;begin + Framesamples < nsamples;frame++){
int low,high;
// Look for starting frame sync
if(startsync == SYNC_FAIL){
// No endsync from previous frame, find initial sync
while(1){
startsync = fft_sync_search(&samples[begin],0,(int)Framesamples,begin);
if(startsync != SYNC_FAIL){
startsync += begin;
break;
}
begin += Framesamples; // Skip a frame time and try again
printf("Start sync search failure, skip to %'d\n",begin);
}
}
assert(startsync != SYNC_FAIL);
// Look for ending frame sync
// Start halfway through the frame, but actually search the middle
// of the result, which straddles the next sync. Only search in the
// allowable range to keep the clock from being driven into the weeds by noise
while(1){
start = startsync + Framesamples/2;
low = 0.5 * Framesamples - clock_tolerance; // very tight tolerance, +/- 5 samples
high = 0.5 * Framesamples + clock_tolerance;
endsync = fft_sync_search(&samples[start],low,high,-1);
if(endsync != SYNC_FAIL){
endsync += start;
break;
}
// Go back to look for another start sync
begin = startsync + Framesamples;
printf("End sync search failure, skip to %'d\n",begin);
startsync = SYNC_FAIL;
goto again;
}
// Got both start and end sync, proceed
i = startsync/Samprate;
printf("Frame %'d @ sample %'d (%'d:%02d)\n",frame,startsync,i/60,i % 60);
// Update estimate of sample clock rate et al
#if 0 // Hack - not let it change
Framesamples = endsync - startsync; // Actual samples in current frame (int)
Symbolsamples = Framesamples/(2*FRAMEBITS); // Actual samples in symbol (float)
Symrate = Samprate / Symbolsamples;
#endif
printf("Symbol rate: %'.3lf Hz; samples/sym: %'.3lf; samples/frame: %'.1lf\n",
Symrate,Symbolsamples,Framesamples);
#if 0
// If clock estimate has changed a lot, regenerate the sync vector with the new clock
if(abs(SYNCBITS*Samprate/Symrate - Synclen) > Symbolsamples/10.){
printf("Clock changed; regenerate sync\n");
generate_sync(Symrate);
}
#endif
// startsync points to the first symbol in the 34-bit sync sequence,
// so we want to skip past it to the first symbol in the new frame
firstsample = SYNCBITS*Symbolsamples + startsync;
for(i=0; i < 2*FRAMEBITS; i++){
double sum;
int midpoint,last;
ind = firstsample + i * Symbolsamples;
midpoint = firstsample + (i+0.5)*Symbolsamples;
last = firstsample + (i+1.0)*Symbolsamples;
// Integrate bit, remove manchester
sum = 0;
for(;ind < midpoint;ind++) // first half of symbol
sum -= samples[ind];
for(; ind < last;ind++)
sum += samples[ind];
sum += 128; // Offset-128 for Viterbi decoder
symbols[i] = (sum > 255) ? 255 : ((sum < 0) ? 0 : sum); // Clip to range 0-255
}
// We start with the encoder having just transmitted these five fixed bytes,
// 3 bytes of coder dump and 2 bytes of sync:
// 12 fc 81 9f be
init_viterbi224(vd,0x819fbe);
update_viterbi224_blk(vd,symbols,FRAMEBITS);
chainback_viterbi224(vd,data,FRAMEBITS,0x819fbe);
maxmetric = max_metric_viterbi224(vd);
minmetric = min_metric_viterbi224(vd);
for(i=0; i<128; i++){
printf("%02x",data[i]);
if((i % 16) == 15)
putchar('\n');
else
putchar(' ');
}
// Re-encode and compare to received symbols to count channel errors
encode(nsymbols,data,FRAMEBITS/8,0x819fbe);
symerrors = 0;
for(i=0;i<2*FRAMEBITS;i++){
if(nsymbols[i] != (symbols[i] > 128)){
symerrors++;
#if 0
printf("sym error %d: %d != %d\n",i,nsymbols[i],symbols[i]);
#endif
}
}
printf("Viterbi path metric range %'d - %'d, diff %'d\n",minmetric,maxmetric,maxmetric-minmetric);
if(symerrors){
double esn0;
esn0 = erfc1(2.*symerrors/(2*FRAMEBITS)); // Amplitude ratio
esn0 *= esn0; // square to get power ratio
// ebn0 = 2 * esn0 for rate 1/2 code
printf("re-encode symbol errors: %'d/%'d; estimated Eb/No = %.2lf dB\n",
symerrors,2*FRAMEBITS,10*log10(2*esn0));
} else {
printf("No re-encode symbol errors; estimated Eb/No > %.2lf dB\n",10.5); // hack; 7.5 dB has a BER < 1/2048
}
putchar('\n');
fflush(stdout);
startsync = endsync;
again:;
}
delete_viterbi224(vd);
exit(0);
}
