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Custom Decoder #4

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Custom Decoder #4

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6da5280
Fix compiler warning
george-hopkins Feb 1, 2017
cc924a5
Avoid reserved characters in output filenames
george-hopkins Feb 1, 2017
db92c5f
Add option to specify custom decoder
george-hopkins Feb 1, 2017
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9 changes: 9 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,15 @@ To use this on very slow systems it helps to increase the priority of rtl_sdr an
This approach requires ```pv``` to also be installed.
With the priority increase and buffering the Raspberry PI for example can demodulate 2 to 3 channels at the same time as long as they do not transmit for many minutes at a time.

### Custom Decoder

Instead of saving each channel to a file, a custom decoder can be specified. The command receives two arguments: The frequency and the time elapsed since the start. The following example shows a simple wrapper script to decode AFSK1200 on the fly:

$ cat decode.sh
#!/bin/sh
rtl_fm -f $1 -s 22050 -P -C -i 46 -t 5 - | multimon-ng -t raw -c -a AFSK1200 -A >$1-$2.log
$ rtl_sdr -f ... | fm_multimix -f ... -c ./decode.sh


Warning
-------
Expand Down
75 changes: 39 additions & 36 deletions demod_proc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -27,14 +27,15 @@
#include <unistd.h>
#include <fcntl.h>
#include <time.h>
#include <sys/wait.h>
#include "fft.h"
#include "demod_proc.h"

demodproc* bin_list[FFT_LEN];
demodproc* short_proc_list[FFT_LEN];
int process_count=0;

int create_process(int bin, long long int totalread, int filter_sub, int center_freq, int fast, int squelch)
int create_process(int bin, long long int totalread, int filter_sub, int center_freq, int fast, int squelch, char* command)
{
int i;
int in[2], out[2], pid;
Expand All @@ -44,8 +45,6 @@ int create_process(int bin, long long int totalread, int filter_sub, int center_

if((pid=fork()) == 0)
{
char cmdstring[255];
int filt_bot;
char datestr[200];
time_t t;
struct tm *tmp;
Expand All @@ -62,56 +61,60 @@ int create_process(int bin, long long int totalread, int filter_sub, int center_

close(in[0]);
close(out[1]);
if(filter_sub)
{
filt_bot=300;
}
else
{
filt_bot=0;
}

t = time(NULL);
tmp = gmtime(&t);
if (tmp == NULL) {
perror("gmtime");
exit(EXIT_FAILURE);
}
// ISO8601 date/time format
if (strftime(datestr, sizeof(datestr), "%FT%TZ", tmp) == 0) {
if (strftime(datestr, sizeof(datestr), "%Y%m%d-%H%M%S", tmp) == 0) {
fprintf(stderr, "strftime returned 0");
exit(EXIT_FAILURE);
}

if(fast)
int frequency = (bin-(FFT_LEN/2))*SAMP_RATE/FFT_LEN+center_freq;
long long int elapsed = totalread/SAMP_RATE/2;

if(command)
{
char frequency_str[20];
char elapsed_str[20];
snprintf(frequency_str, 20, "%d", frequency);
snprintf(elapsed_str, 20, "%lld", elapsed);

fprintf(stderr, "Starting decoder: %s %s %s\n", command, frequency_str, elapsed_str);
execlp(command, command, frequency_str, elapsed_str, (char*)NULL);
}
else if(fast)
{
char squelch_str[20];
char filestr[255];
snprintf(filestr, 255, "%d_%s_%lld.pcm", (bin-(FFT_LEN/2))*SAMP_RATE/FFT_LEN+center_freq, datestr, totalread/SAMP_RATE/2);
snprintf(filestr, 255, "%d_%s_%lld.pcm", frequency, datestr, elapsed);
snprintf(squelch_str, 20, "%d", squelch);
fprintf(stderr, "writing raw 22050Hz 16bit audio to %s\n", filestr);
execlp("rtl_fm", "rtl_fm", "-s", "22050", "-P", "-C", "-i", "46", "-t", "5", "-l", squelch_str, filestr, (char*)NULL);

perror("Failed to start child process");
exit(1);
fprintf(stderr, "Writing raw 22050Hz 16bit audio to %s\n", filestr);
execlp("rtl_fm", "rtl_fm", "-s", "22050", "-P", "-C", "-i", "46", "-t", "5", "-l", squelch_str, filestr, (char*)NULL);
}
else
{
fprintf(stderr, "writing audio to %d_%s_%lld.wav\n", (bin-(FFT_LEN/2))*SAMP_RATE/FFT_LEN+center_freq, datestr, totalread/SAMP_RATE/2);
snprintf(cmdstring, 255, "rtl_fm -s 22050 -P -C -i 46 -l %d -t 5 - |"
"sox -t raw -r 22050 -e signed-integer -b 16 -c 1 -L - "
"-r 8000 %d_%s_%lld.wav sinc %d-3000 -n 16 ",
squelch,
(bin-(FFT_LEN/2))*SAMP_RATE/FFT_LEN+center_freq,
datestr,
totalread/SAMP_RATE/2, filt_bot);

execl("/bin/sh", "sh", "-c", cmdstring , (char *)NULL);

fprintf(stderr,"Failed to start child process\n");
exit(1);
char cmdstring[255];
char filestr[255];
snprintf(filestr, 255, "%d_%s_%lld.wav", frequency, datestr, elapsed);
snprintf(cmdstring, 255, "rtl_fm -s 22050 -P -C -i 46 -l %d -t 5 - | "
"sox -t raw -r 22050 -e signed-integer -b 16 -c 1 -L - "
"-r 8000 %s sinc %d-3000 -n 16",
squelch,
filestr,
(filter_sub ? 300 : 0)
);

fprintf(stderr, "Writing audio to %s\n", filestr);
execl("/bin/sh", "sh", "-c", cmdstring, (char *)NULL);
}

fprintf(stderr, "Failed to start child process\n");
exit(1);
}

newproc->pid=pid;
Expand Down Expand Up @@ -161,7 +164,7 @@ void end_process(demodproc* proc)
int i;
close(proc->outpipe);
close(proc->inpipe);
waitpid(proc->pid, NULL);
waitpid(proc->pid, NULL, 0);
bin_list[proc->bin]=0;
free(proc);

Expand All @@ -187,8 +190,8 @@ int get_process_count()
return process_count;
}

void check_processes(double* bins, int* freqs, int freqcount,
long long int total_read, int misses, int center_freq, int filter_sub, int fast, int squelch)
void check_processes(double* bins, int* freqs, int freqcount,
long long int total_read, int misses, int center_freq, int filter_sub, int fast, int squelch, char* command)
{
int i,j;
int miss =1;
Expand All @@ -206,7 +209,7 @@ void check_processes(double* bins, int* freqs, int freqcount,
{
fprintf(stderr, "Creating process to demodulate %d Hz\n",
(freqs[i]-(FFT_LEN/2))*SAMP_RATE/FFT_LEN+center_freq);
create_process(freqs[i],total_read,filter_sub,center_freq, fast, squelch);
create_process(freqs[i], total_read, filter_sub, center_freq, fast, squelch, command);
}
miss =0;
bin_list[freqs[i]]->detection_misses=0;
Expand Down
6 changes: 3 additions & 3 deletions demod_proc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -43,15 +43,15 @@ typedef struct demodproc_struct
}
demodproc;

int create_process(int bin, long long int totalread, int filter_sub, int center_freq, int fast, int squelch);
int create_process(int bin, long long int totalread, int filter_sub, int center_freq, int fast, int squelch, char* command);
void end_process(demodproc* proc);

demodproc** get_process_list();
int get_process_count();

//checks if process exists and creates if not,
//should handle small frequency instabilities
void check_processes(double* bins, int* freqs, int freqcount,
long long int total_read, int misses, int center_freq, int filter_sub, int fast, int squelch);
void check_processes(double* bins, int* freqs, int freqcount,
long long int total_read, int misses, int center_freq, int filter_sub, int fast, int squelch, char* command);

#endif
17 changes: 13 additions & 4 deletions fm_multimix.c
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Original file line number Diff line number Diff line change
Expand Up @@ -59,6 +59,7 @@ int filter_sub=0;
struct circ_buf circ_buffer;
int fast_mode=0;
int squelch=0;
char* command=0;

void mix_signal(demodproc* proc, uint8_t* inbuf, uint8_t* outbuf)
{
Expand Down Expand Up @@ -162,7 +163,7 @@ int read_data()
}
}
check_processes(results, freqs, freq_count, samples_read,
detection_misses, center_freq, filter_sub, fast_mode, squelch);
detection_misses, center_freq, filter_sub, fast_mode, squelch, command);
}
skip = 120;
}
Expand Down Expand Up @@ -247,8 +248,9 @@ void arg_msg()
"\tbefore recording will stop (default 10, approx 10 seconds)]\n"
"\t[-s Filter out sub audible (<300 Hz) tones.]\n"
"\t[-S Speed boost. Turns of nice features like output filtering\n"
"\tin an attempt to improve speed. (default off)]\n"
"\t[-l Squelch level passed to rtl-fm. (default 0)]\n"
"\tin an attempt to improve speed. (defualt off)]\n"
"\t[-c The command which is executed to decode a channel]\n"
);
exit(1);
}
Expand All @@ -259,7 +261,7 @@ int main(int argc, char *argv[])
int running =1;
int opt;

while ((opt = getopt(argc, argv, "f:t:m:vsSl:")) != -1)
while ((opt = getopt(argc, argv, "f:t:m:vsSl:c:")) != -1)
{
switch (opt)
{
Expand All @@ -284,6 +286,9 @@ int main(int argc, char *argv[])
case 'l':
squelch = (int)atoi(optarg);
break;
case 'c':
command = optarg;
break;
default:
arg_msg();
break;
Expand Down Expand Up @@ -340,7 +345,11 @@ int main(int argc, char *argv[])
{
arg_msg();
}


if(command && (filter_sub || squelch)) {
fprintf(stderr, "Filters can not be applied when a custom decoder is used.\n");
exit(1);
}

for(i=0;i<freq_count;i++)
{
Expand Down